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Effects of corrected color temperature on spatial brightness perception
Abstract
The relationship between lamp color characteristics and brightness perception is not well known. In this study, nine lighting environment with correlated color temperature (3000 K, 5000 K, and 8000 K) and illuminance (1000 lx, 300 lx, and 100 lx) were created. Both the side by side visual matching and spatial brightness scaling experiments are designed to verify the effects of correlated color temperature on spatial brightness perception. The results of the study show that lighting with high correlated color temperature will have stronger spatial brightness perception than lower ones. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011
... The luminance quantity and CCT of references affect human visual perception and responses that are fundamentally linked to their visual comfort and satisfaction . Most national and international lighting design guides recommend a lighting level with high CCT (Ju, Chen, & Lin, 2012). Figure 3 illustrates the relationship between CCT and illuminance of an ambient illumination based on Kruithof (1941) study. ...
... Figure 3 illustrates the relationship between CCT and illuminance of an ambient illumination based on Kruithof (1941) study. According to the Kruithof curve, humans prefer lower CCT when the illuminance is lower, and prefer higher CCT when the illuminance is higher (Ju et al., 2012). Moreover, combinations of CCT and illuminance that lie in the upper shaded areas in Figure 3 are perceived as excessively unnatural and colourful; those in lower shaded spaces are viewed as dim and cold (Boyce & Cuttle, 1990). ...
... However, other studies have suggested that there is no association between CCT and perceived brightness (Hu, Houser, & Tiller, 2006;Park, Chang, Kim, Jeong, & Choi, 2010;Fotios, 2017). Overall, Ju et al. (2012) state that there is not any consensus on the relationship between CCT and perceived brightness to enhance indoor visual comfort. Aschehoug et al. (2000) defined adaptation as the process by which the state of the human visual system is modified by previous and present exposure to stimuli that may have various luminances, spectral distribution, and angular substance. ...
A high luminance contrast between windows and surrounding surfaces can increase the risk of discomfort glare, which can diminish office workers' satisfaction and productivity. This research explores how increasing the luminance of areas surrounding the window using an innovative electric wall-washing system could improve subjective scores for the window appearance, as well as reducing energy bills in office rooms with different window-to-exterior-wall ratios. This study demonstrate that the proposed electric wall-washing system with low power level does efficiently improve window appearance, as well as mitigating problematic interventions in lighting conditions that lead to increased energy consumption in buildings.
... 3,4,[8][9][10][11][12][13][14][15][16][17][18][19][20][21] A fewfull-scale studies have been conducted under LED lighting where the observers have been immersed within the lighting environment. [22][23][24][25] A study by Miller et al. 22 was conducted in a room with spectrally tuneable LED systems and discussed colour rendering of LEDs. Oi et al. 23 compared LED lighting with fluorescent lamp lighting in an indoor environment evaluating brightness and preference. ...
... The study by Huang et al. 24 discussed the effects of the CCT of LED lighting on working attention dealing with brightness along with other aspects. The study by Ju et al. 25 discussed spatial brightness considering different illuminances and CCTs. However, none of these studies [22][23][24][25] was conducted in an office environment. ...
... The study by Ju et al. 25 discussed spatial brightness considering different illuminances and CCTs. However, none of these studies [22][23][24][25] was conducted in an office environment. ...
In order to determine user acceptance for light-emitting diode (LED) office lighting, a full-scale experiment was conducted in two mock-up office rooms with different light spectra at two different illuminances. Six LED spectra and two fluorescent lamp spectra were used for the study. There were four spectra (three LED spectra and one fluorescent lamp spectrum) at a correlated colour temperature (CCT) of 4000 K and four spectra (three LED spectra and one fluorescent lamp spectrum) at a CCT of 6500 K. Forty observers evaluated the lighting environments under different spectra and rated the lighting environments sitting at a working desk and at a meeting table. The observers preferred the task illuminance of 500 lux to 300 lux and the CCT of 4000 K to 6500 K. The observers preferred the spectral power distributions (SPDs) under which they found the lighting environment to look brighter and more spacious. The observers’ preferences showed that spatial brightness was affected by illuminances and SPDs. The lighting with a SPD having higher values of a reference-based metric (CQS Colour Preference Scale) and an area-based metric (CQS Gamut Area Scale or Gamut Area Index) was preferred most at a CCT of 4000 K. It was also found that the lighting with the fluorescent lamp was least preferred among the other SPDs at the CCT of 4000 K. The observers preferred both the simple and complex SPDs over fluorescent lamps at 4000 K in the office environment. It would be a good option to develop simple LED SPDs while maintaining the criteria of good lighting for an office environment.
... A light distribution that comprises upward and downward rays of light enhances the overall perception of brightness and spaciousness in a room [8], and the quality of lighting is rated higher under mixed lighting conditions [9]. In addition, the CCT of light sources also influences the perception of spatial brightness, with studies revealing that lighting with high-CCT lighting has a more dynamic perception of spatial brightness than lighting with low CCT [10]. However, current qualitative research on this topic is limited to evaluating predetermined scenarios and is unable to quantify spatial brightness perception. ...
... In addition, due to the limitations of CCT range, we cannot make accurate predictions when CCT exceeds 5000 K. According to the result of Ju's [10] study, when the color temperature is greater than 5000 K, the difference between spatial brightness gradually decreases. So we decided to optimize the model using log function. ...
Currently, rapid progress in display technology and optical simulation software has enabled the visualization of lighting design, which can provide abundant visual information. However, renderings only allow designers to subjectively judge whether the lighting layout and optical parameters are reasonable. So we want to combine the rendered images and photometric data in the process of optical simulations to define an evaluation indicator of spatial brightness, which can quantify the perceived brightness of the simulated scene. An image assessment experiment based on a display was conducted to investigate the relationship between spatial brightness and calculated image metrics of indoor lit environments. Participants evaluated spatial brightness perception of 39 images of indoor lit environments simulated with SPEOS simulation software on the screen. Four metrics (Log-median luminance, RAMMG contrast, correlated color temperature(CCT) and 60°circular area) were used to characterize participants’ spatial brightness scores, and the relevant prediction equation was proposed. The application of the RAMMG contrast to spatial brightness prediction has a good performance. The image-based assessment method developed in this study has a high Pearson’s correlation coefficient (rp=0.932) with the actual visual assessment, which is reliable and convenient. The proposed model performs better compared with other prediction methods available.
... However, in the present study, 6500 K was perceived as dimmer than 4000 K at 750 lux, which was not consistent with the positive association between CCT and perceived brightness. However, it is important to note that there were several field lighting simulations [108][109][110] that could not find any clear correlation between CCT and perceived dimness. For instance, Park et al. [108] identified that participants perceived 6000 K dimmer than 4000 K, and there was no clear positive or negative association between CCT and perceived dimness through field lighting simulations. ...
... For instance, Park et al. [108] identified that participants perceived 6000 K dimmer than 4000 K, and there was no clear positive or negative association between CCT and perceived dimness through field lighting simulations. Ju et al. [109] conducted field lighting simulations with various combinations of CCT and illuminance levels and found that participants perceived 8000 K slightly dimmer than 5000 K at 300 and 1000 lux. Given such inconsistent results, more studies are required for an in-depth understanding of the correlation between CCT, illuminance, and perceived dimness of lighting. ...
Optimizing space utilization in buildings is necessary to achieve a sustainable built environment. To this end, accurate space utilization prediction, considering the spatial preference of occupants, is required to design well-utilized spaces in architecture, engineering, and construction projects. However, there is no existing method for quantitatively estimating occupants’ spatial preferences during space planning and design phases to optimize post-occupancy space utilization. Thus, in this study, an immersive choice modeling approach (ICMA) was developed to estimate the spatial preferences of occupants by integrating a discrete choice modeling approach with an immersive virtual environment simulation. The ICMA quantitatively estimates the spatial preferences of occupants in three steps: 1) discrete choice experiment design, 2) immersive virtual environment choice simulation creation, and 3) spatial preference modeling. The ICMA was successfully demonstrated by estimating the spatial preferences of 45 participants for an office. The application of an ICMA was then illustrated through a case example, highlighting its ability to predict space utilization in space planning and design phases.
... However, most of the previous research disagreed with this conclusion and found that at the same photopic level a light source with higher CCT would produce better visual accuracy when compared with a light source with lower CCT [59][60][61][62]. Because, it has been proven that under a high CCT light source the brightness perception of observers would be improved [63,64] and their pupil size would reduce, which may enhance visual acuity [59,65]. In our achromatic ring chart test the mean value of error_a for the seven luminous environments ranged from 0.44 to 1, meaning participants hardly made any mistakes for all the environments (with a total of 96 rings in one chart). ...
... The effect of luminous environment with different CCT on brightness has also been investigated by many studies. Most of the studies found that lighting with high CCT resulted in a stronger brightness perception than lower ones [64,[78][79][80]. However, some studies indicated that warm luminous environment will enhance the perception of brightness [15,81]. ...
Daylighting has been associated with improved mood, enhanced morale, increased visual comfort and reduced fatigue. Glazing with varying transmittance, colour or configuration may have significant effects on the quality and quantity of daylight within a building, thus good glazing design has posed significant challenges for building designers. Colored glazing is broadly applied in modern offices worldwide and many studies have explored the effect of this glazing on human performance. Commonly studied are chromatic glazing typologies which offer a unidirectional shift in the colour of light to either bronze or blue. This alters the spectral ability of the glazing and thus changes the indoor luminous environment. It is reported that although occupants prefer warm light, people perform better under cool light condition. This project aims to implement patterns in chromatic glazing to introduce a two-directional colour distortion to alter the colorimetric characteristics of the glazing, heavily affecting the user's perception and performance in the luminous environment. More specifically, seven different indoor luminous conditions were created using various patterned chromatic glazing (100% CAR Blue, 70% CAR Blue, 30% CAR Blue, neutral clear glazing, 30% CAR Bronze, 70% CAR Bronze, and 100% CAR Bronze) to investigate their effect on human perception using a scaled test room (1:3 scaling) to simulate office working conditions. Both subjective (questionnaire on pleasantness, comfort, alertness) and objective (an achromatic Landolt ring test and a chromatic Landolt ring test) evaluations were carried out for the proposed window conditions. The results suggest that the patterned chromatic glazing conditions create a more desirable luminous indoor environment, as well as a more efficient working environment. The 30% blue and 70% blue glazing improved feelings of visual comfort compared to the 100% blue, whilst retaining the efficiency of task completion. Meanwhile the 30% bronze glazing increased the efficiency of task completion compared to the 100% bronze, whilst retaining the ratings for comfort and pleasantness. This implies that the design of patterned chromatic glazing which introduces the combination of two chromatic glazing may be a feasible solution to improve the indoor luminous environment.
... However, in the present study, 6500 K was perceived as dimmer than 4000 K at 750 lux, which was not consistent with the positive association between CCT and perceived brightness. However, it is important to note that there were several field lighting simulations [108][109][110] that could not find any clear correlation between CCT and perceived dimness. For instance, Park et al. [108] identified that participants perceived 6000 K dimmer than 4000 K, and there was no clear positive or negative association between CCT and perceived dimness through field lighting simulations. ...
... For instance, Park et al. [108] identified that participants perceived 6000 K dimmer than 4000 K, and there was no clear positive or negative association between CCT and perceived dimness through field lighting simulations. Ju et al. [109] conducted field lighting simulations with various combinations of CCT and illuminance levels and found that participants perceived 8000 K slightly dimmer than 5000 K at 300 and 1000 lux. Given such inconsistent results, more studies are required for an in-depth understanding of the correlation between CCT, illuminance, and perceived dimness of lighting. ...
In recent decades, immersive virtual environments (IVEs) have enabled users to experience various lighting scenarios with a high sense of presence and immersion, thereby having the potential to simulate office lighting design. To realistically experience lighting design cases in IVE lighting simulations, the CCT and illuminance levels should be accurately reproduced. However, there is still a lack of empirical evidence considering these factors. Thus, this study examined whether CCT and illuminance levels could be accurately reflected in IVE lighting simulations by investigating users’ responses to variations in CCT and illuminance levels in IVEs. To this end, we created nine IVE lighting cases and investigated the responses of participants regarding visual perception (comfort, naturalness, dimness, and warmness) and task performance measured through a questionnaire and the Landolt C test. The results indicated that, although using head-mounted displays affected the perception of visual comfort in some respects, the participants showed responses corresponding to the general findings of field lighting simulations of previous studies. In terms of task performance, participants showed improvement as the illuminance increased in IVEs, while there was no specific relationship between CCT and task performance due to the different effects of CCT on visual acuity and contrast sensitivity. The present study empirically identified the potential of IVE lighting simulations considering CCT and illuminance. With further investigations on more diverse office lighting conditions, IVE lighting simulations will help architects design optimal office lighting.
... Multiple studies reveal that rooms illuminated with higher CCT lamps appear brighter than rooms illuminated with lower CCT lamps, assuming other characteristics like illuminance and luminance distribution are held constant [9][10][11][12]. Akashi and Boyce [13] found that the lamp with CCT 6500 K was the most effective in increasing the brightness in an office setting, ...
... The findings of this study are consistent with previous studies, which reported that lighting with high CCT had stronger brightness [11][12][13][14][15][16]. However, our perception results contradicted those of previous study which were consistent with brightness results, because each study used different perceptive attributes and previous studies did not systematically develop subjective semantic attributes. ...
Illuminance levels have been standardized and regulated for many purposes. However, the effects of correlated colour temperature of lighting have received little attention in the field. This study investigated the effects of correlated colour temperature of lighting on the brightness sensation, lighting perception, and cognitive performance of 60 students under ambient light emitting diodes (LED) lighting conditions (CCT: 3000 K, 4000 K, and 5700 K; illuminance: 650 lx and 1050 lx) in an actual university classroom. An increase in correlated colour temperature (CCT) led to an increase in brightness sensation. However, increased CCT did not linearly increase lighting comfort. A CCT of 4000 K was considered as the optimum for lighting comfort in educational settings. But in comparison to comfort, higher levels of perceptual properties, satisfaction and acceptance were not affected by CCT from 3000 K to 5700 K. Scores on the working memory test were significantly affected by CCT and illuminance level in men only. The effects of gender appeared in glare sensation and the working memory test. Women were sensitive to glare sensation and had a lower mean score in the working memory test than men. Optimal CCT is more beneficial than increased illuminance in moderately ambient indoor lighting, as it provides better lighting comfort. Further research can look at the long-term effects of CCT on lighting perception depending on brain processing levels and more diverse and in-depth cognitive performance.
... Both Fotios and McNelis indicated that under the same CRI, the light sources with higher CCT have higher brightness and visual experience and are more preferred [27,28]. Ju pointed out that under the same luminosity, higher CCT light sources have higher brightness visual experiences [29]. Houser and his colleagues utilized statistical tools and confirmed the high correlation between CCT and various common color evaluation standards such as CRI and CQS. ...
... Despite the considerable effect of CCT on color performance, most color evaluation does not take this effect into account. Most studies have highlighted the significant relationship between CCT and brightness experience, and luminosity is often considered in most standard color evaluation metrics [29,34,35]. Thus, the intention of this study was to create a transformation relationship between CCT and luminosity. ...
Luminosity and correlated color temperature (CCT) have gradually become two of the most important factors in the evaluation of the performance of light sources. However, although most color performance evaluation metrics are highly correlated with CCT, these metrics often do not account for light sources with different CCTs. This paper proposes the existence of a relationship between luminosity and CCT to remove the effects of CCT and to allow for a fairer judgment of light sources under the current color performance evaluation metrics. This paper utilizes the Hyper-Spectral Imaging (HSI) technique to recreate images of a standard color checker under different luminosities, CCT, and light sources. The images are then analyzed and transformed into interpolation figures and equal color difference curves. This paper utilizes statistic tools and symmetry properties to determine an exponential relationship between luminosity and CCT in red-green-blue (RGB) LED and OLED light sources. Such a relationship presents an option to remove the effects of CCT in color evaluation standards, as well as provide a guide line for adjusting visual experience solely by adjusting luminosity when creating a lighting system.
... Spatial brightness has also previously been referred to as building lighting, 11 room brightness 12 or scene brightness. 13,14 Many past studies have investigated the influence of spectral power distribution on spatial brightness, [15][16][17][18][19][20][21][22][23][24][25] Fotios et al provide a useful review. 26 Other studies have investigated the relationship between spatial brightness and light on a vertical plane 27 and also luminance within a defined field of view. ...
... However, applying a linear regression model to E h and PAI serves as a useful backward inference as to the relationship experienced between the two items. Modelling the data set as a whole produces no predictable relationship between the two items (R 2 = 0. 19). It can be seen from Figure 6 that three outlying points strongly influenced the regression line. ...
This paper presents a pilot study that investigated the suitability of mean room surface exitance as a predictor of spatial brightness and perceived adequacy of illumination, and then compared these results with how horizontal illuminance predicted both items under the same conditions. The experiment included 26 participants. A small office was used for the study. It exposed participants to three levels of mean room surface exitance, each delivered with three different light distributions and across three different surface reflectances, resulting in a total of 27 light scenes. A clear relationship existed between mean room surface exitance and both perceived adequacy of illumination and spatial brightness, but not between horizontal illuminance and either item. Correlations were drawn between reported levels of spatial brightness and reported levels of perceived adequacy of illumination.
... For 20 studies 12,36,40,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] including the first experiment in Boyce and Cuttle, 44 it was concluded that they did not present credible evidence of SPD and spatial brightness. The reasons for omitting these studies included failure to randomise, or report whether presentation sequences were randomised, 12,53,56,58-60 having a large number of stimuli relative to the number of response options thus leading to a suspected grouping bias, 44,53,56,58-60,62 not reporting sufficient quantitative data or procedural design, 12,36,40,[49][50][51][52][53][54][55][56][57][58][59][61][62][63][64] and not reporting clearly the precise items for which ratings were sought. ...
... For 20 studies 12,36,40,[49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] including the first experiment in Boyce and Cuttle, 44 it was concluded that they did not present credible evidence of SPD and spatial brightness. The reasons for omitting these studies included failure to randomise, or report whether presentation sequences were randomised, 12,53,56,58-60 having a large number of stimuli relative to the number of response options thus leading to a suspected grouping bias, 44,53,56,58-60,62 not reporting sufficient quantitative data or procedural design, 12,36,40,[49][50][51][52][53][54][55][56][57][58][59][61][62][63][64] and not reporting clearly the precise items for which ratings were sought. 52,58,61,64 ...
Light sources are available in a variety of spectral power distributions (SPDs) and this affects spatial brightness in a manner not predicted by quantities such as illuminance. Tuning light source SPD to better match the sensitivity of visual perception may allow the same spatial brightness but at lower illuminance with potential reductions in energy consumption. Consideration of experimental design was used to review 70 studies of spatial brightness. Of these, the 19 studies considered to provide credible evidence of SPD effects were used to explore metrics for predicting the effect of SPD but did not provide conclusive evidence of a suitable metric, in part because of incomplete reporting of SPD characteristics. For future work, these data provide an independent database for validating proposed metrics.
... Spatial brightness (SB), sometimes called scene brightness, is an important aspect of illuminated interiors that describes whether there appears to be more or less light (CIE 2011). While illuminance is an obvious key factor and distribution of light has also been studied, the effect of spectrum on SB has received widespread attention since at least the 1970s (Boyce 1977;Flynn and Spencer 1977;Berman et al. 1990; Boyce and Cuttle 1990;Berman and Liebel 1996 Nov;Fotios and Levermore 1997;Fotios and Levermore 1998a;Fotios and Levermore 1998b;Fotios and Levermore 1998c;Vrabel et al. 1998;Boyce et al. 2003;Fotios and Gado 2005;Tiller et al. 2005;Akashi and Boyce 2006;Hu et al. 2006;Manav 2007;Houser et al. 2009;Vienot et al. 2009;Ju et al. 2012;Royer and Houser 2012;Wei et al. 2014;Baniya et al. 2015;Fotios, Atli, Cheal, Houser, et al. 2015;Fotios, Atli, Cheal, and Hara 2015;Kim et al. 2015;Rea et al. 2016;Bullough 2018;Zele et al. 2018;Yu and Akita 2019;DeLawyer et al. 2020;Ma et al. 2022;Jin et al. 2023;Khanh et al. 2023; Van de Perre et al. 2023;Yu and Akita 2023). Spectrum is an intriguing topic because the potential to hold input power constant while increasing SB could lead to substantial energy savings. ...
An experiment was conducted to evaluate the effect of a spectral power distribution optimized to increase spatial brightness compared to one approximating a typical blue-pump, phosphor converted LED (YAG:Ce). Chromatically- and luminance-adapted participants completed a reading task, visual search task, numerical verification task, and provided ratings for brightness, vividness, warmth, and preference over the course of approximately 20 minutes for each of four lighting conditions (2 SPDs by 2 illuminance levels [nominally 250 lx and 500 lx]). As a final task, the participants chose the brighter SPD between the two SPDs that were alternated every five seconds. In alignment with a past experiment where participants provided ratings after viewing 60 stimuli for about 20 to 30 seconds each, the brightness-optimized SPD was rated as brighter, more vibrant, and more preferred than the PC-like SPD. When evaluated as a choice in a rapid sequential presentation, the brightness-optimized SPD was chosen as brighter than the PC-like SPD 28 out of 30 times. There was not a statistically significant change in spontaneous blink rate (an indicator of visual fatigue) or blink duration, nor any difference in glare, eye fatigue, or eye discomfort. Results for visual performance were mixed.
... A blue filtering system, like #80A, may be utilized with sunshine film (tuned to 5500 K) under hotter light sources, such as candles, incandescent lights, or sunsets. Detailed filters are needed to account for variances in temperature in tungsten lamps, which may range from 3200 K to 3400 K, or for the little blue colour that flashing tubes can teach, which can reach up to 6000 K [21] . ...
... There has been mixed evidence regarding the role of CCT (and chromaticity more broadly) on SB perception. While several studies have suggested that increasing CCT increases SB (Boyce and Cuttle 1990;Boyce et al. 2003;Akashi and Boyce 2006;Vienot et al. 2009;Baniya et al. 2015;Ma et al. 2022;Jin et al. 2023;Van de Perre et al. 2023), others have not (Tiller et al. 2005;Hu et al. 2006;Manav 2007;Houser et al. 2009;Ju et al. 2012;Royer and Houser 2012;Kim et al. 2015;Yu and Akita 2023), and at least one study found the opposite (Hu et al. 2022). In several of these experiments, CCT was the only metric used to operationalize SPD; however, CCT is a coarse metric and other spectrally derived measures (e.g., color rendition, Duv) can vary substantially at constant CCT. ...
... Since the CCT range of lighting is specified by international standards [8,9], it is limited to 2700 K to 6500 K in the simulation. This covers the CCT requirements of actual lighting scenarios and is consistent with the CCT range that can be adjusted by current commercial LED luminaires [25]. ...
Correlated color temperature (CCT) is an important parameter of the phosphor-converted LED (PC-LED); international standards specify its range in different scenarios. However, little has been done to investigate the effect of CCT on the performance of visible light communication (VLC). In this paper, we propose an analytical model for the transmission performance of an LED VLC system based on the dual components of blue and yellow light from the luminescence mechanism of the PC-LED. On this basis, the effects of CCT on the PC-LED’s input current and output optical power between the dual components are analyzed. The simulation results show that the increase of CCT expands the modulation bandwidth of the PC-LED, and the trend of the BER with CCT is also related to the transmission data rate. In addition, the maximum data rate of the PC-LED with CCT from 2700 K to 6500 K under a certain transmission distance is also simulated in this paper.
... There has been mixed evidence regarding the role of CCT (and chromaticity more broadly) on SB perception. While several studies have suggested that increasing CCT increases SB (Akashi and Boyce 2006;Baniya et al. 2015;Boyce and Cuttle 1990;Boyce et al. 2003;Jin et al. 2023;Ma et al. 2022;Van de Perre et al. 2023;Vienot et al. 2009), others have not (Houser et al. 2009;Hu et al. 2006;Ju et al. 2012;Kim et al. 2015;Manav 2007;Royer and Houser 2012;Tiller et al. 2005;Wei et al. 2014b;Yu and Akita 2023), and at least one study found the opposite (Hu et al. 2022). In several of these experiments, CCT was the only metric used to operationalize SPD; however, CCT is a coarse metric and other spectrally derived measures (e.g., color rendition, Duv) can vary substantially at constant CCT. ...
... Results showed that most observers required less light with higher CCT values to obtain the same apparent brightness. Other studies found similar results in which CCT led to an increase in brightness perception [25][26][27]. In Boyce and Cuttle [28], 15 observers conducted a colour discrimination task in an office. ...
This study explores the impact of wall luminance and correlated colour temperature (CCT) on the observers’ brightness perception and scene preference in a controlled, windowless office environment. A two-interval-forced-choice experiment was conducted with the 20 lighting scenes derived from five CCTs (2500–10 000 K) and four luminances (12–120 cd/m²). The results from 20 observers showed that a higher wall luminance significantly increased brightness. At equal luminances, different CCT values had no significant effect on brightness, consistent with some reports that CCT is not a reliable predictor of brightness when other photometric factors are held constant. Scene preference increased as wall luminance increased to approximately 72 cd/m², but a further increase in wall luminance to 120 cd/m² had no significant impact on preference. As the CCT increased from 2500 K, the preference increased up to approximately 4000 K, followed by a substantial decline from 5715 to 10 000 K.
... Poor distribution of light on vertical surfaces can create glare on computer screens, which leads to uncomfortable work settings and increased stress levels among office workers [61]. Color-correlated temperature is a metric used to describe the color of the light emitted by a source in degrees of Kelvin, with low Kelvin values indicating a warm yellow/red color and high Kelvin values indicating white/blue colors [62]. The literature suggests that low levels of color-correlated temperature provide a sense of relaxation for office workers within their workspace [63]. ...
We regularly face stress during our everyday activities, to the extent that stress is recognized by the World Health Organization as the epidemic of the 21st century. Stress is how humans respond physically and psychologically to adjustments, experiences, conditions, and circumstances in their lives. While there are many reasons for stress, work and job pressure remain the main cause. Thus, companies are increasingly interested in creating healthier, more comfortable, and stress-free offices for their workers. The indoor environment can induce environmental stress when it cannot satisfy the individual needs for health and comfort. In fact, office environmental conditions (e.g., thermal, and indoor air conditions, lighting, and noise) and interior design parameters (e.g., office layout, colors, furniture, access to views, distance to window, personal control and biophilic design) have been found to affect office workers' stress levels. A line of research based on the stress recovery theory offers new insights for establishing offices that limit environmental stress and help with work stress recovery. To that end, this paper answers ten questions that explore the relation between the indoor office-built environment and stress levels among workers. The answers to the ten questions are based on an extensive literature review to draw conclusions from what has been achieved to date. Thus, this study presents a foundation for future environmental stress related research in offices.
... This result is in a first way contradictory to the common understanding of lower and higher CCTs to brightness perception. As investigated in previous studies, lower CCTs were associated primarily with brighter brightness perception (Harrington, 1954;Fotios and Levermore, 1997;Ju et al., 2012). But all studies in common, they had primary a spot light distribution, meaning, luminaires positioned at the roof and shining downside only. ...
Illumination preference models are usually defined in a static scenery, rating common-colored objects by a single scale or semantic differentials. Recently, it was reported that two to three illumination characteristics are necessary to define a high correlation in a bright office-like environment. However, white-light illumination preferences for vehicle-occupants in a dynamic semi- to full automated modern driving context are missing. Here we conducted a global free access online survey using VR engines to create 360° sRGB static in-vehicle sceneries. A total of 164 participants from China and Europe answered three levels in our self-hosted questionnaire by using mobile access devices. First, the absolute perceptional difference should be defined by a variation of CCT for 3,000, 4,500, and 6,000 K or combinations, and light distribution, either in a spot- or spatial way. Second, psychological light attributes should be associated with the same illumination and scenery settings. Finally, we created four driving environments with varying external levels of interest and time of the day. We identified three key results: (1) Four illumination groups could be classified by applying nMDS. (2) Combinations of mixed CCTs and spatial light distributions outperformed compared single light settings (p < 0.05), suggesting that also during daylight conditions artificial light supplements are necessary. (3) By an image transformation in the IPT and CAM16 color appearance space, comparing external and in-vehicle scenery, individual illumination working areas for each driving scenery could be identified, especially in the dimension of chroma-, partially following the Hunt-Effect, and lightness contrast, which synchronizes the internal and external brightness level. We classified our results as a starting point, which we intend to prove in a follow-up-controlled laboratory study with real object arrangements. Also, by applying novel methods to display high fidelity 360° rendered images on mobile access devices, our approach can be used in the future interdisciplinary research since high computational mobile devices with advanced equipped sensory systems are the new standard of our daily life.
... Vertical illuminance was found to have significant influence on passenger perception of spatial brightness (Question 11: H = 12.825, P < 0.05; see Table 12 for details). Elsewhere, spatial brightness has been found to be influenced by both spectral power distributions (SPDs) and illuminance [48], especially CCT with shorter wavelength elements [49]. Although brightness perception is related to the SPDs of the illuminant, characterization of spatial brightness by CCT continues to have some limitations [50]. ...
This paper presents a multi-dimensional evaluation and comparison of the visual comfort of the cabin lighting environments of five subways lines in Chengdu. The study proposes a visual comfort evaluation procedure that integrates objective and subjective methods combined with existing visual comfort measurement methods. Based on this evaluation procedure, the lighting conditions (illuminance and glare) in each cabin were measured using an illuminance metre and high-dynamic image technology, and an online questionnaire was used to understand passengers’ subjective experiences of cabin lighting. The results show that: seating layout has no significant influence on the visual performance of mobile phones or on spatial brightness; horizontal illuminance in the lighting environments of subway cabins has no significant influence on task performance of passengers using mobile phones; the overall perception of subway cabin spatial brightness increases with vertical illuminance; and passengers have no obvious preference for a cabin correlated colour temperature.
... The apparent brightness studies the light environment more from the perspective of psychophysical and physiophysical quantities. Because the spectral power distribution of traditional white LED light source differs a lot, with the large scale application of LED, the failure of apparent brightness in the traditional photometric evaluation system is more prominent [3][4][5][6]. At the same time, the visual brightness discrimination threshold is at different lighting levels. ...
This article explores the experimental study on the relationship between human eye discrimination threshold of white light under different lighting levels and color temperatures by the psychophysical experimental method. The visual matching method was applied to study the subjective brightness perception under different lighting environments. We try to explore the internal connection between the physical intensity and subjective rating value. The experimental results will do help the development of dimming system for smart lighting.
... The large variance of illuminance levels reported in the literature to be preferred by users or judged as sufficiently bright in combination with the fact that the corresponding experiments were often performed at significantly different CCTs promote that photometric illuminance alone is not sufficient to properly describe the perceived brightness of the lit environment [11]. Indeed, Boynton [59] argued on the level of cone excitations that also short-wavelength components of a light source's SPD must contribute to its brightness impression, giving an explanation for the observation that light stimuli of equal luminance but different CCTs provoke a distinct brightness perception [60]. Based on previous work by Marks [61], it could be shown that this phenomena particularly depends on the degree of S-cone excitations in such a way that higher CCTs (larger S-cone excitation) are judged brighter than lower CCTs at otherwise equal photometric conditions. ...
Provoking high user acceptance in lighting can be a very challenging task and demands suitable tools for properly modelling and predicting the users’ perception of the lit environment. Recently, a new model formalism based on the perceptually relevant attributes of perceived brightness, visual clarity, and color preference has been introduced and successfully applied in some preliminary studies. However, a proof of the model’s applicability from a lighting practitioner’s point of view for realistic lighting scenarios and use-cases is still pending and should be performed as part of this work. For this purpose, results of two dedicated lighting condition rating experiments representing different lighting contexts are reported. It is shown that the model predictions for all three perceptual attributes exhibit excellent linear correlations with the respective subject mean ratings and, in all cases, correctly predict the test light sources’ rank order. These results clearly emphasize the applicability and practical relevance of the model and confirm the suitability of its multi-dimensional approach.
... Vertical illuminance was found to have significant influence on passenger perception of spatial brightness (Question 11: H = 12.825, P < 0.05; see Table 12 for details). Elsewhere, spatial brightness has been found to be influenced by both spectral power distributions (SPDs) and illuminance [48], especially CCT with shorter wavelength elements [49]. Although brightness perception is related to the SPDs of the illuminant, characterization of spatial brightness by CCT continues to have some limitations [50]. ...
Lighting in the subway passenger compartments is one of the many factors influencing riding comfort. The research and design of lighting evaluation system for subway passenger compartments aim to establish evaluation standard and models for the design of light environments in this area. By using the virtual simulation technology of optical software Dialux and referring to the existing lighting standards in China, Lighting Evaluation System 1.0 (LES 1.0), a light environment evaluation system for subway passenger compartments, is developed. In the process of visual simulation, the lighting scenes of subway passenger compartments are simulated to obtain comfort evaluation index data for evaluating the comfort. On this basis, the evaluation process is constructed, including the establishment of the evaluation standard model for light environments. The research is helpful for designers and engineers to improve the design and evaluation of lighting environments in subway passenger compartments in China.
... The respondents evaluated the two test zones as practically equal regarding the driveway light intensity (27:26), while a small majority of the respondents (28:22) were in favor of the 4000 K LEDs for spotting pedestrians. In both cases the illuminated objects (roadway made of asphalt and the pedestrians' clothes) were dark, representing a possible reason for the absence of significant preference for a higher CCT lighting (Ju et al. [52] showed that lighting with a higher CCT is characterized by a stronger spatial brightness perception than the one with a lower CCT, but they did not consider dark spaces). The same explanation is valid for the results referring to the detection of small dark-colored obstacles (a small majority of the respondents (27:22) preferred the lower CCT lighting). ...
The purpose of this study was to initiate broad research aimed to establish the preferred color of light of LEDs from a driver’s point of view. Two street lighting installations (one with 3000 K and the other with 4000 K LEDs) were evaluated both objectively and subjectively. The objective evaluation, realized using a CCD camera, included detection of small targets and pedestrians. A slight advantage was identified for the 3000 K lighting installation regarding both types of target. As for subjective evaluation (realized through a questionnaire), the task of the participants (drivers) was to choose the more appropriate between the two lighting installations regarding six lighting parameters, as well as the overall visibility. The 3000 K LED installation was evaluated as a better solution for most of the analyzed parameters, as well as for the overall visibility. However, only the results regarding the color of light (in favor of the 3000 K LEDs) and detection of small light-colored obstacles (in favor of 4000 K LEDs) were convincing, which was confirmed by the statistical analysis. Due to the obtained mild preference for the 3000 K LEDs and several limitations/challenges of the conducted surveys, it was concluded that additional research is needed in order to decide on the preferred color of light of LEDs from a driver’s perspective.
... At 500 lx and 750 lx, the observers' mean rating for perceived brightness was statistically significantly highest under 5000 K. This result supports the finding of previous works [18][19][20] which found that observers' impressions of brightness increased with an increased CCT. The observers' mean rating for the apparent spaciousness of the room was also highest under 5000 K at all three illuminance levels. ...
In order to study the preferred combination of the illuminance level and correlated colour temperature (CCT) and the preferred CCT of different ethnic groups in office lighting, a full-scale experiment was conducted in an office room with a light-emitting diode (LED) luminaires. Fifty-three observers from three different ethnic groups (Asian, European and African) rated nine different preset lighting situations after performing different office activities. The combination of 750 lx with 4000 K was statistically significantly preferred for office lighting. It was also found that the impression of brightness increases with a higher CCT and that people feel more stimulated under a higher CCT compared to a lower CCT. The European group preferred a lit environment under CCT 4000 K for office lighting and with the Asian and African groups the preference between 4000 and 5000 K depends upon illuminance levels.
... 12,13 Cuttle proposes MRSE with the intention that it would be a proxy for the quantity of light arriving at the eye, which could also be represented by the indirect illuminance on a vertical plane at eye level. Many past studies have investigated the influence of spectral power distribution on spatial brightness, 9,14,15,16,17,18,19,20,21,22,23,24,25 whilst others have examined the influence of light on a horizontal or vertical plane 26 and within a defined field of view. 27,28 Rea et al found better correlations with brightness between illuminance measured on a vertical plane than with that measured on a horizontal plane. ...
This paper presents a pilot study that has investigated the suitability of mean room surface exitance as a predictor of spatial brightness and compared these results with how horizontal illuminance predicts spatial brightness under the same conditions. The experiment took a group of 26 participants and, using a scaled booth, exposed each participant to three levels of mean room surface exitance, each delivered with three different light distributions and three different surface reflectances, resulting in a total of 27 light scenes. Results demonstrated that, under the range of conditions to which participants were exposed, a systematic relationship existed between mean room surface exitance and spatial brightness, but not between horizontal illuminance and spatial brightness.
... illuminance) and the quality of light (i.e. CCT) are the most relevant parameters to understand the possibility to reduce electrical needs in the indoor space and hence to achieve energy saving and to assess the quality of the environment perceived (Lutfi Hidayetoglu et al., 2012;Clements-Croome, 1977;Boyce and Cuttle 1990;Ju et al., 2012), moreover related to their correlation, affecting the users in performing medium or accurate visual tasks (Mills et al., 2007;Pinto et al., 2008). Finally, the color render index R a , commonly used to evaluate the performance of artificial lighting, becomes interesting as a colored transparent surface is integrated into the building envelope and lot of cases can be found in which the color of the envelope is not previously evaluated in the design phase implying visual discomfort for the user and reduced capacity to perform detailed visual tasks. ...
The paper deals with the integration of a luminescent solar concentrator (LSC) realized with a yellow dye produced by ENI Donegani Institute and analyzed by Politecnico di Milano. The LSC component has the capability to produce electricity and substitute transparent surfaces into the building envelope using inclinations (e.g. vertical walls) and orientation (e.g. different from south) not optimal for standard photovoltaic system integration. The visual effects of the dyed LSC integration are analyzed to understand potentials and critical points of the use of such a component in the built environment. Systematic tests were conducted to evaluate the visual performance parameters related to the application of the yellow LSC component as fanlight in a partially glazed south façade of an office space, through experimental measures taken on a scaled physical model. The main effects can be ascribed to the increasing of the illuminance level and to the reduction of correlated color temperature whereas the color render index shows changes that in some cases have to be carefully assessed such as when color identification is the specific visual task.
... When considering illumination in commercial buildings, the S/P ratio is sometimes simplified to CCT (for computational details of CCT see: Ohno, 2014). Lamps with higher S/P ratios also tend to have higher CCTs (Ju, Chen, & Lin, 2012;New Buildings Institute, 2003;Steffy, 2008). The New Buildings Institute has stated that 4100 K lamps will appear brighter than 3000 or 3500 K lamps (New Buildings Institute, 2003). ...
This paper describes a field study concerning the effects of correlated color temperature (CCT) and lumen output of fluorescent lighting on office workers' perceptions and visual comfort. Four luminous conditions were created and organized as a two by two factorial design, comprising two levels of CCT (that is, 3500 and 5000 K) and lumen output (that is, 2330 and ≈ 3000 lm). Participants experienced a baseline condition followed by the four treatment conditions and then returned to the baseline condition; each treatment lasted two weeks. Twenty-six participants adapted to the luminous conditions in the first week of each treatment period. In the second week they completed brief assessment surveys three times daily using smart phones. Participants completed a more comprehensive survey on the last day of each treatment period. CCT was found to be a significant factor affecting perceptions of brightness, visual comfort, and satisfaction of color temperature. There were interaction effects between CCT and lumen output and between CCT and the presence or absence of a window. The luminous conditions with higher CCT (that is, visually cooler) or higher lumen output were rated to be brighter than those with lower CCT (that is, visually warmer) or lower lumen output. Participants judged the luminous condition with both higher CCT and higher lumen output as being too bright. CCT was the only statistically significant factor for perceived visual comfort and the satisfaction of color temperature. The luminous conditions at 5000 K were regarded as less comfortable than those at 3500 K. 5000 K was judged to be too cool when the higher lumen output lamps were in place. For the participants with daylight in their office, 5000 K was especially judged to be too cool.
... When considering illumination in commercial buildings, the S/P ratio is sometimes simplified to CCT (for computational details of CCT see: Ohno, 2014). Lamps with higher S/P ratios also tend to have higher CCTs (Ju, Chen, & Lin, 2012;New Buildings Institute, 2003;Steffy, 2008). The New Buildings Institute has stated that 4100 K lamps will appear brighter than 3000 or 3500 K lamps (New Buildings Institute, 2003). ...
This study aimed to explore the differences in the subjects' sustained attention under the impact of nine lighting conditions consisting of the combination of three commonly used correlated color temperature (CCT) (3300 K, 4300 K, and 5300 K) and illuminance levels (300 lx, 500 lx, and 750 lx) to provide guidance on the adjustment of CCT and illuminance level parameters for indoor lighting. We selected 24 physically and mentally healthy university students (12 male and 12 female) as the experimental subjects. The subjects were required to perform sustained attention to response task (SART) activities under the nine different lighting conditions and collected the alpha (α) waves (8–12 Hz) from the electroencephalography signals. Subsequently, the mean power spectral density of the α waves and various SART parameters were analyzed and tested. Finally, the effects of different CCT and illuminance levels on the subjects' attention were compared. With the increase in CCT, the attention level tended to increase linearly, whereas the attention level was the lowest at 300 lx and the highest at 500 lx and appeared as an inverted “U” shape. The subjects' attention level was the highest at the combination of CCT of 5300 K and illuminance level of 500 lx and the lowest at the combination of CCT of 3300 K and illuminance level of 500 lx. These results provide important data to elucidate the impact of lighting condition on attention.
Despite a rapid transition to LED lamps, it is still little knowledge about the effects of these light sources on users with low vision. The study’s main objective was to acquire a better understanding about how correlated colour temperatures (CCTs) of non-directional LED affect visual accessibility and perceptions of lighting quality in homelike environments among visually impaired persons. The study took place in a full scale laboratory in which CCTs of 2,700 K and 4,000 K were tested. Participants having normal vision (N=60, 24 males, 36 females, M = 25.50) were divided into three groups of 20 to assess the two lit environments with cataract goggle, severe cataract goggle and normal vision respectively. They were asked to perform everyday activities while the observer recorded the time and conducted observations, and to rate the difficulty of each activity. Thereafter, the participants were asked to rate their perceptions of lighting quality and contrasts in the room. With the same CRI of Ra80, there were no differences in the performance of everyday activities between the two CCTs whereas the differences in the perceived lighting quality and the perceived contrasts were found. The cool white CCT was found to positively affect visual accessibility and perceived contrasts however, its comfort quality remains questionable.
This study provides optimal correlated color temperature and illuminance to increase comfort and reduce fatigue by considering psychological and physiological quantities when working with paper and electronic devices. Task performance was not affected by devices and lighting conditions. The subjective evaluation revealed no significant differences between devices. The participants felt tired with an illuminance of 300lx and preferred a correlated color temperature of 5000K or 6500K and an illuminance of 750lx. However, the participants were more comfortable at 3000K and 750lx than at high correlated color temperature and low illuminance. The adjustment method demonstrated that comfortable illuminance does not show a significant difference in correlated color temperature and that paper requires significantly higher brightness levels than a screen. The adjustment method and subjective evaluation found consistent results for comfortable illuminance. Physiological measurements revealed that oxygenated hemoglobin was higher for computer than for paper use. In addition, illuminance of 500lx and correlated color temperature of 5000K resulted in the least fatigue. Although the subjective evaluation found no significant differences in fatigue, physiological measurements revealed that illuminance and correlated color temperature were accompanied by the least fatigue. Therefore, the results of this study highlight the necessity of creating a work environment that considers psychological and physiological quantities based on the work medium.
In this study, two experiments were conducted to investigate the effects of the color rendering index (CRI) and correlated color temperature (CCT) of light-emitting diode (LED) lighting on office user acceptance and to explore the proper color attributes for human-centric office lighting. Experiment 1 had four LED lights, with two levels for the CRI (CRI < 80: 79, 76; or CRI ≥ 80: 83, 84) and CCT (3000 K or 6500 K) at 300 lux. In experiment 2, there were four LED lights, with several levels for the CRI (CRI < 80: 78; or CRI ≥ 80: 87, 83) and CCT (3000 K or 6500 K) at 500 lux. Ninety-six participants in experiment 1 and ninety-four participants in experiment 2 performed a reading task. The results in experiment 1 and experiment 2 showed that LEDs with lower CRI values at warm color temperatures were rated as more acceptable than LEDs with higher CRI values at warm color temperatures. However, the positive effect extended to LEDs with higher CRI values at cool temperatures but not to LEDs with lower CRI values at cool temperatures. Therefore, the findings are that LEDs with lower CRI values at warm color temperatures and LEDs with higher CRI values at cool temperatures provide the right level of color attributes for office lighting.
This research tries to identify lighting parameters that can influence human perception in immersive virtual environments (VEs). As a testing platform, an immersive VE was created, in order to investigate whether light intensity, light distribution and correlated color temperature can affect spatial perception of an immersive VR space.
The study of human perception in virtual environments has been a fruitful research field for several decades. Whereas it was found that there is a disparity between judgments of distance in a VR space, as well as a consistent underestimation of the size of the environment and distance to objects [1, 2], little research is based on the effects that lighting parameters have on human perception in immersive VEs.
The present study explores the influence of light intensity, light distribution (beam angle) and correlated color temperature (CCT) of light sources on relative distance perception (exocentric distance), stereopsis (3d surface/depth perception), perception of the directionality of light sources and perception of brightness, in an immersive VE [3, 4]. The results presented arrive from several test sessions with randomly selected individuals participating in VR walkthroughs with different lighting conditions in a simulated VE.
This research is based on VR walkthrough test sessions that consisted of 90 randomly selected participants aged between 18 to over 70 years, divided into three groups for testing different lighting scenarios. Different lighting scenarios were created for each of the test groups. Two of the groups explored the effects of CCT, while the third group focused on the effects of different light intensities and light distribution. For each group, a subjective quantitative assessment was carried out, as there is no validated objective method in a perception-centric system, as is the case of VR [5].
The participants were required to enter a simulated VE and were informed beforehand that they would be asked questions, while instructions were also given on what to observe from specific points of view. The answers were recorded in real time by an interviewer, in order to obtain data more accurately.
The VE was modeled after the Erechtheion Caryatids area of the New Acropolis Museum in Athens, Greece, from architectural plans that were kindly provided by the architects, along with additional in-situ measurements and photographs, in order to produce a real scale experience model. The model was realized using 3ds Max for the geometry of the building and Unreal Engine for the materials, the lighting and the programming language used for the real-time simulation of the VE. The technical equipment, consisted of an Oculus Rift CV1 VR headset with a pair of motion controllers and three tracking sensors, connected to a custom workstation PC.
Results from the virtual walkthroughs show that, lower color temperatures (warmer light), and narrow beam light distributions, influence both the perception of the direction of light sources, as well as stereopsis (depth perception), while higher color temperatures (cooler light) affect the perception of spatial brightness. These results also support real world experiments [6] that show that higher color temperatures have an effect on perceived spatial brightness. However, none of the aforementioned scenarios showed significant effects on the subjective perception of exocentric distances. The study concludes with demographic results showing perception differences between genders and age.
Kruithof’s graph identifies combinations of illuminance and correlated
color temperature (CCT) alleged to yield pleasing visual conditions for interior
lighting. Though in research terms the support provided by Kruithof is insufficient,
it is widely cited as a design rule and has been the focus of many experimental studies
despite evidence against Kruithof since at least 1990. The current article examines
the trends displayed in those studies considered to provide credible evidence: these
do not support Kruithof. For pleasant conditions, these data suggest only avoiding
low illuminances and do not favor any CCT.
The luminescent solar concentrator (LSC) could provide a colorful and adaptable complement to standard silicon solar panels, allowing easier deployment solar energy systems in the urban environment. In order to successfully implement this technological innovation into the built environment, it should also complement the surrounding architecture and be visually acceptable to the user. One prominent feature of the LSC is its bright, fluorescent coloration. Since the devices can be transparent, this opens the possibility of employing the LSC as a power-generating window. Current research on LSCs focused on the energy efficiency and on the theoretical impact on users. So far, the impact of such a colored window on the inhabitants (or users) in spaces using these windows has been largely unexplored. In this work, we study the impact of a red LSC on the visual comfort and impression of volunteer participants. We made the interesting observation that a window covered 25% by an LSC is judged favorably when compared to a normal, clear glass window. Such a window could become a local source of electrical power from sunlight while simultaneously improving the well-being of the room inhabitants.
Various luminous environments can be created by utilizing light emitting diode (LED) lights which can be easily controlled with diverse illuminance and correlated colour temperature (CCT) levels. Implementation of such luminous environments could affect occupants’ perceptions. This study aim to identify subjective brightness perception of young healthy female and male students being exposed to different CCT conditions of LED lights in lecture room environment. To measure brightness perception, three subjective evaluations were conducted. First, brightness perception in different CCTs was compared under single CCT LED lights. Second, a single CCT of LED light was compared to the same CCT under mixed CCTs. Third, different mixing methods for a particular CCT were applied to mixed CCTs of LED lights. The results of the first test showed that the subjects perceived the environmental space to be brighter when exposed to a higher CCT with the same illuminance level. The second experiment showed that LED lights with mixed CCTs are relatively superior to LED lights with a single CCT in terms of brightness perception under the same illuminance level. The third experiment illustrated that the subjects would feel their environment as brighter when exposed to higher CCT and/or with a larger proportion of high CCT. The selections and mixing among different CCTs for classroom design can be determined based on the results of this study where brightness perception is important.
Since the Kruithof's work on general illumination, the relationships between correlated color temperatures (CCTs) and human behavior are well documented. In the recent years, because of the high growth of light-emitting diode (LED) lighting products, studies on the effects of LED lighting on human behavior have emerged. This study examines the effects of CCTs on focused and sustained attention under white LED desk lighting. Three CCT conditions (2700, 4300, and 6500 K) are examined, and the Chu Attention Test was used to measure focused and sustained attention. Results show that CCTs affect attention. In specific, the 4300 K condition resulted in a significantly better focused and sustained attention. Comfortableness and clarity are rated by the subjects. The self-reported comfort shows no significant differences among the three conditions, but clarity shows significant differences. Gender differences are also discussed. It is found that the self-reported clarity by males show no significant differences among the three lighting conditions, whereas the self-reported clarity by females is significantly lower when CCT is 2700 K. © 2014 Wiley Periodicals, Inc. Col Res Appl, 2014
A feature of many national lighting standards is the recommendation that lamps with high correlated colour temperatures should not be used at low illuminances. The technical justification for this advice is limited so two experiments have been conducted to explore its validity. In the first experiment, fifteen observers carried out colour discrimination tasks and assessed the lighting of a small room lit to different illuminances using lamps with good colour rendering properties but with different correlated colour temperatures. The room decor was achromatic but natural colour, in the form of fruit and flowers, was introduced as another variable. In the second experiment, ten observers carried out colour discrimination tasks and made assessments of the lighting of the same room lit to 225 lx, but decorated with blue or pink walls and lit by lamps with good colour rendering properties but different correlated colour temperatures. Again, natural colour, in the form of fruit and flowers, was introduced as another variable. Analyses of the assessments of the lighting of the room showed that one major factor determining the impression given by the lighting was the illuminance. Increasing the illuminance made the lighting of the room appear more pleasant, more comfortable, clearer, more stimulating, brighter, more colourful, more natural, more friendly, more warm, more uniform, less hazy, less oppressive, less dim and less hostile. The correlated colour temperature of the lamps used had virtually no effect on the observer's impression of the lighting of the room. The other major factor influencing the impression of the lighting of the room was the presence of natural colour. Introducing natural colour, in the form of fruit and flowers, enhances the positive impressions created by the lighting, particularly at the higher illuminances. This enhancement occurs regardless of the correlated colour temperature of the lamps being used. It can be concluded that the advice limiting the use of high correlated colour temperature lamps in rooms lit to low illuminances is unnnecesarily restrictive. The results obtained suggest that provided the occupants are fully adapted to the lighting the correlated colour temperature of the lamp has little effect on people's impressions of the lighting of the room.
The perception of room brightness over photopic luminances ranging from 30 cd m-2 to 67 cd m-2 was judged by 12 subjects in an almost uniformly white experimental chamber. Two different illuminants were compared which had different spectral compositions, but were colour matched. Brightness judgements were often opposite to large differences in photopic luminance. These results are inconsistent with models of brightness perception that depend solely on cone receptors. At the luminance levels considered here subjective evaluation of light intensity depends upon both photopic and scotopic spectral contributions. These results imply that aspects of the visual system operate mesopically under most interior lighting conditions.
Two screens viewed side by side were illuminated by radiations approximating those of blackbodies of different color temperatures and matched in brightness at photopic levels. A group of 73 observers found that less light of the higher color temperature was needed to produce equality of brightness than would be required by the CIE normal observer. The average gain in apparent brightness was 1 percent per 100°K color temperature difference in the range 5400–6300°K. The gain decreases with the age of the observer.
When 27 of the observers re-matched the screen colors using a “flicker” method, no gain in apparent brightness was obtained. Thus the CIE normal observer properly predicts equality of brightness under the experimental conditions used if the observer is allowed to respond only to brightness (flicker method). If the observer has time to color adapt, as in continuous side by side screen viewing, an increase in the apparent brightness of the higher color temperature screen results.
This study examines the belief that rooms illuminated with higher correlated color temperature (CCT) lamps will appear brighter than rooms illuminated with lower CCT lamps at the same illuminance. This belief is held by many illuminating engineers and lighting designers, despite the fact that it is not supported by theory, and has received mixed support in experimental studies. The linear brightness models of Guth and Howett, and the nonlinear color appearance models of Nayatani and Hunt predict that higher CCT sources will appear dimmer than lower CCT sources, though the predicted brightness differences are small. We report results from two experiments to test the predictions of these models. Both experiments involved the visual comparison of two identical side-by-side full-scale rooms. One room was illuminated with lamps having a nominal CCT of 3500K; the other room was illuminated with lamps having a nominal CCT of 6500K. All other photometric characteristics of the two rooms were held constant and the rooms were identically furnished as mirror images with typical office furniture. In the first experiment forty-one subjects used a forced choice survey instrument to identify which room appeared brighter. In the second experiment twenty-eight subjects used a dimming adjustment task to match the brightness in the two rooms. No relationship was found between CCT and perceived room brightness in either experiment. Evidence from linear brightness models, nonlinear color appearance models, and the results of the psychophysical experiments reported here suggests that that there is no relationship between CCT and the perception of interior brightness. Although brightness perception is related to the spectral power distribution of an illuminant, CCT is too limited to characterize the relationship between source color and perceived brightness.
This paper reviews previous work exploring apparent brightness in interior spaces, in particular the relationship between lamp spectrum and illuminance. An understanding of this is beneficial to designers of interior lighting and to researchers investigating visual response to lighting. The review establishes reliable data from previous work, examines the correlation between descriptors of lamp colour properties and illuminance, and identifies some further work required. © The Chartered Institution of Building Services Engineers 2001.
Many offices are illuminated at levels much higher than necessary for office tasks. Lowering ambient illuminance, while maintaining task illuminance, i.e., task-ambient lighting, can save energy without impairing visual performance. A downside of task-ambient lighting is rooms appear dark and gloomy. Maintaining brightness perception is the key to success in task-ambient lighting. To examine the practicality of brightness-enhanced task-ambient lighting for illuminance reduction a field study was conducted in a modern office setting. This study examined office workers’ responses to approximately one-third lower ambient illuminance than the initial illuminance and two measures designed to enhance brightness perception: higher correlated color temperature lamps (6500K) and sparkle elements. Surveys showed that after an initial adaptation period, office workers were generally satisfied with the lower level of ambient lighting. They did increase their use of task lighting at their desks but this had little impact on overall energy consumption. The 6500K lamp was effective at increasing perceptions of brightness in offices with the lower ambient light level. Over a longer period, the sparkle elements used did not significantly change workers’ perceptions of gloom.
Melanopsin, a novel photopigment, has recently been localized to a population of retinal ganglion cells that display inherent photosensitivity. During continuous light and following light offset, primates are known to exhibit sustained pupilloconstriction responses that resemble closely the photoresponses of intrinsically-photoreceptive ganglion cells. We report that, in the behaving macaque, following pharmacological blockade of conventional photoreceptor signals, significant pupillary responses persist during continuous light and following light offset. These pupil responses display the unique spectral tuning, slow kinetics, and irradiance coding of the sustained, melanopsin-derived ganglion cell photoresponses. We extended our observations to humans by using the sustained pupil response following light offset to document the contribution of these novel ganglion cells to human pupillary responses. Our results indicate that the intrinsic photoresponses of intrinsically-photoreceptive retinal ganglion cells play an important role in the pupillary light reflex and are primarily responsible for the sustained pupilloconstriction that occurs following light offset.