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TESTING THE USE OF SPECTRALLY TUNABLE LIGHTING SYSTEMS TO IMPROVE COMFORT, ALERTNESS AND SLEEP QUALITY IN INDOOR WORKING ENVIRONMENTS

Authors:
PP29
TESTING THE USE OF SPECTRALLY TUNABLE LIGHTING
SYSTEMS TO IMPROVE COMFORT, ALERTNESS AND
SLEEP QUALITY IN INDOOR WORKING ENVIRONMENTS
Aleix Llenas et al.
DOI 10.25039/x46.2019.PP29
from
CIE x046:2019
Proceedings
of the
29th CIE SESSION
Washington D.C., USA, June 14 – 22, 2019
(DOI 10.25039/x46.2019)
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Llenas, A. et al. TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO IMPROVE ...
TESTING THE USE OF SPECTRALLY TUNABLE DYNAMIC LIGHTING SYSTEMS TO
IMPROVE COMFORT, ALERTNESS AND SLEEP QUALITY IN INDOOR WORKING
ENVIRONMENTS
Llenas, A.1,2 *, Hurlbert, A.3, Lam, F.4, Manudhane, R.4, Gaurav, G.3, Giddings, J.4, Carreras, J.2
1 Institut de Recerca en Energia de Catalunya (IREC), Barcelona, SPAIN, 2 Ledmotive Technologies
SL, Barcelona, SPAIN, 3 Newcastle University, Newcastle upon Tyne, UNITED KINGDOM, 4 Arup,
London, UNITED KINGDOM.
* allenas@ledmotive.com
DOI 10.25039/x46.2019.PP29
Abstract
Lighting installations in offices and buildings are typically static and specified in terms of their
effects via the classical visual pathway (e.g. chromaticity or brightness). It is now rec ognised
that spectral variations in light elicit non -visual effects, including on emotion and cognition, via
a distinct neural pathway, and it is important for health and wellbeing to take these into account.
This article describes the aims and methodology of an experiment designed to test whether
dynamic sculpting of the light spectra in indoor environments , either to mimic natural daylight
changes or achieve particular levels of non-visual vs. visual stimulation, may elicit different
biological and behavioural effects. Subjective and objective measurements are used to assess
the behavioural responses resulting from exposure to custom -made, dynamically changing light
spectra sequences that are produced by a spectrally tunable lighting system, and to compare
these with responses to a traditional fluorescent lighting system. The viability of the study is
qualitatively evaluated here; quantitative results will be reported el sewhere.
Keywords: spectrum, colour, LED, metameric, CCT, melanopic lux, melanopsin , lighting, smart
lighting, tunable, multi-channel
1 Introduction
The modern human visual system evolved under exposure to natural daylight only, for millennia.
Natural daylight is a mixture of light from the sun and sky, containing energy at all wavelengths
in the visible spectrum. Since the invention of the candle, perhaps 2500 years ago, humans
have become more reliant on artificial lighting technologies, and increasingly so in the past
century after the development of electric light, with more activities being performed indoors,
significantly shortening the daily exposure to natural light.
In the design of illumination for indoor spaces, it has traditionally been only the well-established
visual effects of light that are considered, such as illuminance, glare, chromaticity or correlated
colour temperature (CCT) , and colour rendering indices (e.g. CRI or TM-30). Yet the recent
discovery of the intrinsically photosensitive retinal ganglion cells as the origin of the non-visual
pathway that entrains biological rhythms to the light/dark circadian cycle (LUCAS et al., 2014)
(BERSON et al., 2002) has started a new drive to characterise lighting in terms also of its non -
visual effects on human behaviour. This non-visual pathway is responsible not only for
regulating the circadian rhythms of body temperature, melatonin secretion, and the overall
sleep/wake cycle, but also for modulating cognitive function, attention, and mood (CAJOCHEN,
2007) (CHELLAPPA et al., 2011) (BADIA et al., 1991). Although it has long been known that
the entraining light signal emanated from the retina (SCHEER, 1999) (LEWY et al., 1980) it was
not until the discovery of the ipRGCs (BERSON et al., 2002) (VANDEWALLE et al., 1996) and
the characterisation of the melanopsin photopigment they contain that the importance of
spectral variations in light for eliciting non-visual effects was fully recognised. The spectral
sensitivity of melanopsin peaks at 480 nm, midway between the short- and middle-wavelength
cones, but is broad-band and overlaps with that of all four classical photoreceptors. Modulation
of the short-wavelength (“blue”) content of light has been shown to affect various physiological
measures such as melatonin suppression, alertness, thermoregulation, heart rate, cognitive
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performance, and electroencephalographic dynamics (BONMATI-CARRION et al., 2014)
(REVELL et al., 2007).
The effectiveness of a given light spectrum in activ ating the non-visual pathway may be
quantified by its melanopic lux, the spectral irradiance weighted by the melanopsin spectral
sensitivity function and integrated over wavelength (Lucas et al. 2014), or by functions of the
same (e.g. CS, REA et al. 2010). Melanopic lux is therefore an appropriate characteristic of
illumination to consider in addition to visual factors such as photopic lux or CCT.
Currently, the most common artificial light sources are fluorescent lights and white LEDs which
are all static sources with spectra very different from natural daylight. The recent invention of
narrow-band LEDs enables the development of spectrally tuneable light sources that are able
to generate illuminations with arbitrary spectral shapes, and therefore to mimic daylight spectral
patterns or create tailored dynamic spectral sequences according to the end -user needs
(SCHUBERT, 2005).
Previous studies have compared the performance of individual subjects under different artificial
lighting conditions (e.g. VIOLA et al., 2008). Such studies, though, have used only two types of
white light, both fixed in time: cool blue-enriched fluorescent light and warm fluorescent light,
and have not exploited the novel spectral flexibility obtainable from multi-channel LED light
sources.
In this study, and for the first time in a real office setting, the behavioural effects of a dynamic
spectrally tunable lighting system are investigated and compared to a traditional fixed
fluorescent lighting system. The study includes assessments of alertness, mood, sleep quality,
performance, mental effort, and other responses to different dynamic illumination conditions in
a 9-week intervention using subjective and objective measurements.
2 Experiment design
This experiment aims to investigate the effects of novel spectrally tunable light-engines that
produce custom-made dynamic illumination sequences during daytime workhours in an office
setting. The aim is to assess whether sculpting different spectral power distributions (SPDs) of
light may bring measurable benefits in terms of well-being and productivity in an indoor
workplace installation, and, more generally, to understand better the behavioural effects of
different lighting conditions in indoor environments and raise awareness of the importance of a
circadian lighting approach.
This investigation took place from February 18th to April 19th 2019 at a multinational professional
services firm headquartered in London, United Kingdom. An area of approximately 160 square
meters was selected, comprising the working desks of 24 people. A set of 36 downlighter
luminaires containing LEDMOTIVE (model VEGA07) tunable light engines were installed into
ceiling panels alongside the pre-existing fixed fluorescent light tubes. External light sources
were blocked by completely covering the windows along one wall, and inserting a scrim between
this space and the adjacent working area (see Figure 1).
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Figure 1 Photograph of the office with Ledmotive’s spectrally tunable lighting system
installed.
The habitual start and end time of the workday are 08:00 and 18:00, respectively. Sunrise varied
from 07:09 at the beginning of the study period to 05:57 at its end; dusk varied from 17:20 to
20:03. Thus, for most of the study, dawn and dusk happened outside the workhours, and
exposure duration to light during this period, including the commute time to and from work, will
have varied from the beginning to the end of the study.
The study duration was 9 weeks. The lighting conditions were: first, 2 weeks under the pre-
existing traditional fluorescent lights only (baseline); second, 2 weeks under the spectrally
tunable light sequence A; third, 2 weeks under the spectrally tunable light sequence B; fourth,
1 week of the spectrally tunable lights mimicking the baseline traditional fluorescent lights
output; and, lastly, 2 weeks under the spectrally tunable lights mimicking the current daylight
patterns. Light sequence A had temporally changing melanopic lux, photopic lux and CCT
during the day, with melanopic lux falling from a high of 45 0 in the morning to a low of 160 in
the evening, photopic lux falling from 500 in the morning to 300 in the evening, and the CCT
changing from cool (6000) to warm (2500) over the same interval. Light sequence B matched
light sequence A in terms of its changing melanopic lux, but kept constant photopic lux and CCT
at levels matching the baseline fixed fluorescent lights. Table 1 summarizes the different light
conditions and the parameters (CCT, photopic lux and melanopic lux) that remain static or
changing.
Table 1 Summary of the trial’s light conditions.
Light condition
Duration
Photopic lux
Melanopic lux
CCT
Baseline (Fluorescent
lights)
2 weeks
Static (350 lx)
Static (160 lx)
Static (3534 K)
Sequence A
2 weeks
Changing (500 lx
300 lx)
Changing (450 lx
160 lx )
Changing (6000
K 2500 K)
Sequence B
2 weeks
Static (350 lx)
Changing (450 lx
170 lx)
Static (3534 K)
Baseline (mimicking
fluorescent lights)
1 week
Static (350 lx)
Static (160 lx)
Static (3534 K)
Real-time daylight
matching
2 weeks
Changing
Changing
Changing
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15 employees (age range 25 57; 6 males), having diverse roles within the company,
volunteered to take part in the study. All participants completed health screening
questionnaires, including screenings for sleep disorders, depression, anxiety, physical illness,
and extreme chronotypes; none were excluded on the basis of these assessments. All gave
their written informed consent prior to any study procedures. The participants were not informed
of the specific lighting conditions to be used or the expected outcomes of the study.
3 Subjective and objective measurements
Throughout the study period, each participant took part in daily subjective and objective
behavioural assessments as follows.
3.1 Subjective measurements
Participants were asked to complete web-based questionnaires at four timepoints (1-4) each
weekday (Monday-Friday), and at two timepoints (1 and 4) on each day of the weekend
(Saturday-Sunday) and holidays. Specifically:
Waking (timepoint 1): Sleep diary, morning entry: after waking up, participants
completed questions assessing the quality of the previous night ’s sleep.
Morning (timepoint 2): Between 10:30 and 11:00h, participants completed a
questionnaire combining the Karolinska Sleepiness Scale (KSS) (AKERSTEDT et al.,
1004) (GILLBERG et al., 1994), the Rating Scale Mental Effort (RSME) (VERWEY et al.,
1996) and Positive and Negative Affect Scale (PANAS) (CRAWFORD et al., 2004).
Afternoon (timepoint 3): In mid-afternoon (16:00h), participants were asked to repeat
the combined questionnaire of KSS, RSME and PANAS.
Evening (timepoint 4): Before going to sleep, participants were asked to complete
questions about sleepiness, mood, drinks and exercise during the day, and to assess
their level of headache and eye strain.
Every Friday, participants were also asked to complete questions on their subjective experience
of the lighting condition experienced that week.
3.2 Objective measurements
Subjective assessments were complemented with objective measurements. More specifically:
Actigraphs recordings: All participants were asked to wear a wearable smart watch
24/7 that keeps track of temperature, light exposure and activity levels.
Short perceptual experiments: Participants completed a short (5 minutes) visual
attention task at two timepoints (2 and 3) each weekday. The task was a continuous
performance task which assessed sustained attention, implemented via a web-based
JavaScript application, presented in black-and-white.
4 Light conditions
4.1 Baseline
The light conditions set for the first two weeks were regular fluorescent lights, some of the most
used light sources in the world. Its spiky spectrum (see Figure 2, left) is very well -known and
totally different from natural daylight. The office’s fluores cent lights had a CCT of 3550K and
typical values of photopic lux at the desktop were about 350 lx. The melanopic lux for this light
was about 160 lx at the desktop. During the 7th week, when mimicking fluorescent lights with
the spectrally tunable light source (see Figure 2, right), the light generated had the same
parameters: CCT of 3550K, photopic lux of 350 lx and melanopic lux of 160 lx at the desk level.
Figure 3 shows that with these light conditions, the three indicators remain static during the
whole working day.
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Figure 2 Baselines: Real fluorescent lights SPD (left) and spectrally tunable light engine SPD
(right). Both measured spectra have the same CCT of 3550K, same photopic lux of 350 lx and
same melanopic lux of 160 lx at desk level.
Figure 3 In an office setting with only fluorescent lights, light indicators such as CCT,
photopic lux or melanopic lux coming from the light fixtures remain static during the whole
working day.
4.2 Light sequences
The LEDMOTIVE (model VEGA07) tunable light engine used for this experiment is composed
of 48 commercial monochromatic LEDs arranged in 7 channels, each with a distinct peak
wavelength, spread over the visible spectrum (see Figure 4).
Figure 4 CIE 1931 xy coordinates of the 7 channels that define the colour gamut (a) and the
preset SPDs of the 7 LED channels (b).
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High melanopic lux in the morning is thought to lead to better attention and higher arousal,
while low melanopic lux in the evening is suitable for relaxing and for better sleep at night (TE
KULVE et al., 2017). This experiment adds to the existing knowledge by using spectrally tunable
light systems with light sequences tailored to human needs. In this experiment, light sequence
A was designed to change in CCT from cool in the morning to warm in the afternoon, and with
photopic and melanopic lux values changing from high values in the morning to low values in
the afternoon (see Figure 5). Sequence B was designed with the same visual parameters as
baseline (same CCT and same photopic lux) but with changing melanopic lux values during the
day (see Figure 6). By comparing sequence B with baseline, the experiment compared the
effects of changing melanopic lux alone, with the other parameters remaining the same. With
sequence A, we are able to test not only the melanopic lux effect, but also the effect of a
concomitant changes in CCT, as the visual comfort and overall experience that the light fixtures
evoke is also important for well-being.
Figure 5 (left) Sequence A was designed to have a changing CCT, changing photopic lux and
changing melanopic lux during the day. (right) In-situ measured spectra from Sequence A
SPD, varying from 9 am (blue) to 6 pm (red).
Figure 6 (left) Sequence B was designed to have the same static CCT and photopic lux as
baseline during all the day, but with changing melanopic lux. (right) In-situ measured spectra
from Sequence B SPD, varying from 9 am (blue) to 6 pm (red).
4.3 Real-time daylight matching
During the trial’s final two weeks, a calibrated spectrometer in the building’s roof was installed
that was able to measure daylight spectra every few seconds. The spectrometer, connected to
a Raspberry Pi, sends the spectral information to the lighting system control unit, which, very
fast, finds the channel weights that give the best spectral fitting to the target SPD (LLENAS et
al., 2019). Any change in CCT or illuminance in the outdoor environment was smoothly
translated inside the office.
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5 Conclusions
This article elaborates on an experiment that was conducted during 9 weeks in an office setting
without interfering with employees’ daily tasks or normal work-load. Different light conditions
were used to test whether by designing custom-made SPDs of light in a dynamic way, it is
possible to elicit benefits in participant’s sleep patterns, alertness, mental effort and mood. The
final results will be published elsewhere.
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The immediate psychophysiological and behavioral effects of photic stimulation on humans [bright light (BL) of 5K lux or dim light (DL) of 50 lux] were assessed in male subjects (N = 43) under four different conditions. For one condition the same subjects (N = 16) received alternating 90-min blocks of BL and DL during the nighttime h (2300-0800 h) under sustained wakefulness conditions. A second condition was similar to the first except that subjects (N = 8) received photic stimulation during the daytime hours. For the third and fourth conditions different subjects received either continuous BL (N = 10) or continuous DL (N = 9) during the nighttime hours. For the nighttime alternating condition body temperature decreased under DL but either increased or maintained under BL. For the continuous light condition, body temperature dropped sharply across the night under DL but dropped only slightly under BL. Sleepiness was considerably greater under DL than under BL, and the difference became larger as the night progressed. Similarly, alertness, measured by EEG beta activity, was greater under BL, and nighttime performance on behavioral tasks was also generally better. There were no differential effects between BL and DL on any measure during the daytime. These data indicate that light exerts a powerful, immediate effect on physiology and behavior in addition to its powerful influence on circadian organization.
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The present experiment used an intraindividual design to investigate the meaning and measurement of "good sleep". Each of 16 subjects slept in an isolation unit according to a schedule (15 sleeps) designed to give variable quality of sleep. Self-rated sleep measures (from the Karolinska Sleep Diary) were obtained after each sleep and subjected to intraindividual regression analyses across time. Most subjective sleep measures showed a strong covariation across conditions. Subjective quality of sleep mainly involved variables of sleep continuity, in particular, perceived calmness of sleep and sleep efficiency. "Sleep quality," "calm sleep," "ease of falling asleep," and ability to "sleep throughout" the time allotted strongly covaried and formed an index of sleep quality. Self-rated ease of awakening deviated from the general pattern and was associated with poor sleep quality. So was reported dreaming (related to awakenings). It was concluded that most subjective sleep measures tend to covary across conditions and that "good sleep" is mainly a question of sleep continuity.
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Light synchronizes mammalian circadian rhythms with environmental time by modulating retinal input to the circadian pacemaker—the suprachiasmatic nucleus (SCN) of the hypothalamus. Such photic entrainment requires neither rods nor cones, the only known retinal photoreceptors. Here, we show that retinal ganglion cells innervating the SCN are intrinsically photosensitive. Unlike other ganglion cells, they depolarized in response to light even when all synaptic input from rods and cones was blocked. The sensitivity, spectral tuning, and slow kinetics of this light response matched those of the photic entrainment mechanism, suggesting that these ganglion cells may be the primary photoreceptors for this system.