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Energies 2020, 13, 4276; doi:10.3390/en13164276 www.mdpi.com/journal/energies
Article
Blue-Light Levels Emitted from Portable Electronic
Devices Compared to Sunlight
David Baeza Moyano 1,*, Yolanda Sola 2 and Roberto Alonso González-Lezcano 3
1 Department of Chemistry and Biochemistry, Universidad San Pablo CEU, Campus Montepríncipe,
Alcorcón, 28668 Madrid, Spain
2 Group of Meteorology, Department of Applied Physics, University of Barcelona, Martí i Franquès 1,
08028 Barcelona, Spain; ysola@meteo.ub.edu
3 Architecture and Design Department, Escuela Politécnica Superior, Universidad San Pablo CEU,
Campus Montepríncipe, Boadilla del Monte, 28668 Madrid, Spain; rgonzalezcano@ceu.es
* Correspondence: baezams@ceu.es
Received: 19 July 2020; Accepted: 14 August 2020; Published: 18 August 2020
Abstract: Over recent years, a technological revolution has taken place in which conventional
lighting has been replaced by light emitting diodes (LEDs). Some studies have shown the possibility
that blue light from these artificial sources could have deleterious effects on the retina. Considering
that people spend a non-negligible time in front of screens from computers and mobile phones, the
eyes receive blue light of different intensities depending on the source. Nevertheless, any study
about the visual and non-visual effects of blue light must consider precise measurements taken from
actual artificial sources. For this reason, we have analyzed the spectral emission of 10 different
electronic devices and weighted them according to the hazard caused by blue light to the eyes,
comparing the results with solar radiation simulated with a radiative transfer model. The maximum
spectral irradiance of the measured electronic devices at 10 cm from the detector was located
between 440 nm and 460 nm. The irradiance for blue light hazard ranged from 0.008 to 0.230 Wm−2
depending on the particular characteristics of each electronic device. In contrast, the solar radiances
in the same spectral range are larger both under clear and cloudy conditions.
Keywords: indoor light; electronic device emission; blue light hazard; sunlight
1. Introduction
The rapid development of new technologies arising from scientific research since the end of the
20th century have resulted in the emergence of multiple portable electronic devices, as well as
illumination systems based on light emitting diodes (LED). The large number of applications has
significantly changed people’s daily lives [1] and has improved the efficiency and light quality of
illumination in residential and private sectors [2]. There is currently a continuous effort to improve
the efficiency of LEDs, both for semiconductor materials and the driver circuit [3,4].
The spectral emission of LED lamps is centered at visible wavelengths, including an important
fraction of blue light. The exposure to blue light has a key role in the regulation of the circadian
rhythms of sleep–wakefulness through its influence on photoreceptor cells in the retina [5]. Blue light
also produces other non-visual effects, such as the inhibition of pineal melatonin production, an
increase in heart rate and the stimulation of cortisol secretion [6–8]. Since blue light acts as a
neurophysiological stimulant, several therapeutic effects have been described, from depression [9] to
a reduction of blood pressure [10]. Besides the positive influence, some studies have indicated
negative effects on the balance of circadian cycles and on the quality of sleep after long exposures to
blue light, mainly from mobile phones [11]. On the other hand, some studies have also reported
Energies 2020, 13, 4276 2 of 9
negative effects on the eye retina, most of which are based on the analysis of cells that were irradiated
with blue light. Nakanishi-Ueda et al. [12] detected oxidative cellular damage on cultivated cells of
bovine retinas when they were exposed to blue (470 nm) LED light with a high irradiance of 48 Wm−2.
Similar results were observed for rat retinas under 10 Wm−2 irradiance exposure [13]. Moreover,
Nakamura et al. [14] irradiated pigmented mice and found damage to the retinal pigment epithelium
and photoreceptors after 3-day exposure to 1100 lux of blue LED light (456 nm). Similarly, Chamorro
et al. [15] radiated human retinal pigment epithelial cells with different LED colors—blue (468 nm),
green (525 nm) and red (616 nm)—as well as white light in 12 h light–dark cycles and observed cell
DNA damage and apoptosis.
The increasing number of studies about the possible negative effects of artificial blue light,
together with the rapid development of new devices during recent years, has been a cause for concern
for the authorities responsible photobiological safety. In 2011, the European Standard EN12464-
1:2011:E, which controls the light in indoor work places, mentioned the need to limit blue light
sources [16], and in 2013, the International Commission on Non-Ionizing Radiation Protection
(ICNIRP) published guidelines that included safety levels to avoid health disorders [17].
Additionally, the ICNIRP published an action spectrum for blue light hazards [18], describing the
effectiveness of each wavelength to cause harm to the retina due to its photochemical effect, as well
as safe exposure limits.
A controversial aspect of this research is that, in some studies, the selected values used to
irradiate samples were not comparable to the common blue light-emitting devices available for most
of the population. For this reason, real measurements of this kind of device, as well as comparisons
with natural ambient light, are necessary. In this respect, O’Hagan et al. [19] published a pioneer
study analyzing the spectral emission of many electronic devices, concluding that none of them could
be associated with eye harm due to the low radiance in the blue spectral range.
The objective of the present study is to analyze the spectral emissions of a sample of portable
electronic devices and compare them with solar radiation under different conditions. This analysis
widens the number of spectra previously measured by O’Hagan et al. [19]. With this purpose, we
have measured different types of electronic devices that are commonly used, such as smartphones,
laptops and electronic tablets. The analysis has focused on biologically active irradiance according to
the blue light hazard action spectrum.
2. Materials and Methods
In this study, we have measured the spectral irradiance from multiple electronic devices at
different distances from their source. The measurements were performed with a double
monochromator spectroradiometer Irradian SR9910 V7 (Irradian SL) from 300 to 600 nm with a 1 nm
spectral resolution. Before each scan, the spectroradiometer automatically performed a zero
measurement to determine dark conditions. Good maintenance and regular calibrations of
spectroradiometers are key to precise spectral measurements. For those reasons, every two years, the
spectroradiometer—as well as the guide light—has been calibrated both in terms of irradiance and
wavelength in the Institute of Optics of the Spanish Scientific Research Council. The calibration is
traceable to the National Standard for Luminous Intensity and Luminous Flux. This
spectroradiometer was previously used in other studies regarding emissions from LED lamps [11].
The sample consisted of 10 electronic devices (five smartphones, one laptop and four electronic
tablets). The screens showed a blue full-screen image with maximum brightness to establish common
characteristics for all the situations. According to the IEC/EN 62471 standard [20], the measurement
of LED lights should be made at a distance of 20 cm from the source. However, a recent study about
the impact of the smartphone viewing distance on sleep analyzed the typical distances in sitting
positions and found values ranging from about 13 to 30 cm, with lower distances for a lying position
[21]. For these reasons, we decided to measure the irradiance with the sensor located at two distances
from the electronic devices, which were in a vertical position. All measurements were done at a
common distance of 10 cm, but for the second distance, we selected a larger distance of 30 cm for
smartphones and another at 40 cm for tablets and laptops. These distances allowed us to establish the
Energies 2020, 13, 4276 3 of 9
range of irradiances that a user would typically receive, from the shortest distance to a more usual
one.
The spectral irradiances were weighted by the blue light hazard sensitivity (Figure 1). This action
spectrum ranges from 400 to 700 nm, with maximum effectiveness in the 400–500 nm spectral range.
The weighting function decreases by a factor of 10 at about 500 nm and by three orders of magnitude
above 600 nm.
Figure 1. Action spectra for blue light hazard and for photopic vision. The ordinate axis is represented
in a log scale to show the large differences between wavelengths. The two dashed vertical lines
represent the blue light range from 400 to 500 nm.
In some studies related to the effects of blue light on eyes, the emissions of LED lamps were only
characterized by their illuminance in lux without considering the action spectrum for blue light
hazard. The illuminance is the radiant flux received per unit area but weighted with the eye’s
sensitivity to visible light, characterized by the action spectrum for photopic vision. When this action
spectrum is compared with that of the blue light hazard, it is evident that the maximum effectiveness
is centered at different wavelengths; i.e., around 100 nm larger for eye sensitivity. The differences
between both spectra result in different biological irradiances, as shown in Figure 2 for the two
different spectra measured in this study. There are clear differences in the magnitude of the weighted
spectral irradiances and the wavelength of the maximum intensity. In some cases, the blue spectral
range is misrepresented due to the smaller weight in the photopic spectrum. For these reasons, it is
important to obtain reliable measurements of LED lamps and to determine the irradiance for blue
light hazard.
Figure 2. Weighted spectral irradiances for blue light hazard and for photopic vision at 10 cm
determined for one laptop and one mobile phone in the sample.
Energies 2020, 13, 4276 4 of 9
The solar spectra were estimated with the Coupled Ocean–Atmosphere Radiative Transfer
(COART [22,23]) model (https://satcorps.larc.nasa.gov/jin/coart.html). The COART model calculates
the spectral irradiance on a horizontal layer at the Earth’s surface as well as spectral radiances for
multiple directions in the sky. The model includes variables related to the atmospheric radiative
transfer, such as ozone, aerosols and clouds, as well as geographical and temporal coordinates. For
this study, we determined the spectral radiation for clear-sky and overcast conditions for two solar
heights (h): 70° (representative of midday on the summer solstice at mid-latitudes) and 30°
(representative of midday on the winter solstice at mid-latitudes). Under clear-sky conditions, the
model assumes that the highest radiance is obtained from the solar disk and the lowest in a
perpendicular plane to the position of the Sun. On the other hand, under overcast conditions, due to
the thick clouds, the solar rays are completely blocked. For the simulations, we considered a mid-
latitude summer atmospheric profile with no stratospheric aerosols but with urban aerosols close to
the surface.
The solar global radiation received on a horizontal surface has two components: direct and
diffuse radiation. The direct component represents the solar radiation coming from the solar disk,
which is almost not scattered or absorbed by the atmosphere, and the diffuse component represents
the radiation from the sky that has been scattered before reaching the surface. Considering the
characteristics of our study, we analyzed the diffuse irradiance that reaches the Earth’s surface,
ignoring the direct component of the global radiation. Since irradiance considers the entire sky, we
also simulated the sky radiances in the direction determined by the solar height but with an azimuth
angle of 180° and therefore opposite to the Sun’s position.
3. Results and Discussion
Figure 3 shows the measured spectral irradiances from different artificial sources. The maximum
emission of all the measured electronic devices was located between 440 nm and 460 nm, and its
spectral irradiance was lower than 0.012 Wm−2 nm−1. Only one of the tablets shows this highest value
(Figure 3a), but most of the other devices showed a maximum spectral irradiance lower than 0.04
Wm−2 nm−1. The artificial spectra showed a second maximum at 520 nm, but with values lower than
0.002 Wm−2 nm−1. When the detector was located at 30/40 cm from the artificial source, the spectral
irradiance decreased for all wavelengths. Escofet and Bará [24] measured spectral irradiances from
different artificial sources to analyze the impact on circadian rhythms and found similar maximum
spectral values at around 450 nm. Similarly, O’Hagan et al. [19] showed the spectrum from one LED
with a maximum at the same wavelength. The differences in the second maximum are related to the
particular color configuration selected in each study. In our case, blue-colored screens reduced the
intensity of this second maximum in comparison with other studies that used white screens.
The spectral irradiances were integrated from 280 to 680 nm to determine the total emissions.
The electronic devices showed an average total irradiance of 0.099 ± 0.096 Wm−2 and a median of 0.072
Wm−2. In each group of electronic devices, there were some cases with irradiances higher than 0.1
Wm−2; however, most of the electronic devices showed irradiances lower than 0.05 Wm−2. The values
decreased if the distance from the source increased up to 30/40 cm, below 0.05 Wm−2. The total
irradiance was very sensitive to the wavelength interval of integration and the experimental
conditions, making it difficult to compare these values with other previous studies. These values are
lower than those integrated by Escofet and Bará [24], since they measured a white image on a screen;
therefore, there was an increase due to the contribution of longer wavelengths. The integrated
irradiances were lower than the solar diffuse irradiances (in the same wavelength interval) on a
horizontal surface under any of the studied situations. The diffuse irradiance ranged from 60 to 82
Wm−2 (h = 30°–70°) under clear conditions and from 147 to 60 Wm−2 (h = 70–30°), considering overcast
conditions with thick clouds. The differences according to the solar height for both sky situations
were related to the increase in the multiple scattering by clouds.
Energies 2020, 13, 4276 5 of 9
Figure 3. Spectral irradiances measured at 10 cm for different electronic devices: (a) One laptop and
four electronic tablets; (b) five mobile phones.
The measured spectral irradiances were weighted with the blue light hazard action spectrum.
Figure 4 shows this biologically active irradiance for all the electronic devices. As expected, the
maximum values were located at around 450 nm, where there was a coincidence between the
maximum emission and the highest effectiveness for blue light hazard. The contribution of these
electronic devices to blue light hazard was only in the range between 420 to 575 nm. In this spectral
range, the combined effect of low emission and effectiveness resulted in a negligible contribution.
Almost all electronic devices showed spectral weighted irradiances lower than 0.010 Wm−2 nm−1 when
the detector as located at 10 cm; when this distance increased, the values were even lower. On the
other hand, the solar spectral diffuse irradiances weighted by the blue light hazard spectrum were
higher than those from the artificial devices, with values between 0.20 to 0.55 Wm−2 nm−1 at 450 nm
depending on the solar height and the sky conditions.
Energies 2020, 13, 4276 6 of 9
Figure 4. Weighted spectral irradiances for blue light hazard measured at 10 cm for different
electronic devices: (a) one laptop and four electronic tablets; (b) five mobile phones; (c) solar diffuse
spectral irradiance for blue light hazard on a horizontal plane at surface level, simulated with the
Coupled Ocean–Atmosphere Radiative Transfer (COART) model for different altitude heights (h) and
sky conditions.
Energies 2020, 13, 4276 7 of 9
The weighted spectral irradiances were integrated from 380 to 680 nm (Table 1). The blue light
hazard irradiances ranged from 0.01 to 0.29 Wm−2 with an average and median of 0.099 ± 0.096 Wm−2
and 0.072 Wm−2, respectively. The large standard deviation reflected the wide range of device
characteristics. Escofet and Bará [24] showed that the use of hardware filters reduced the spectral
irradiance at these wavelengths. The differences were possibly also related to use of screen filters in
some of the devices, especially in mobile phones. For larger distances from the source, the blue light
hazard irradiances were reduced in more than 80% for most of the cases. These results agree with the
radiances for blue light hazard that were determined for multiple electronic devices by O’Hagan et
al. [19].
Table 1. Weighted irradiances for blue light hazard from 380 to 600 nm at 10 cm and at 35/40 cm
(smartphones/tablets) for the different electronic devices and the estimated solar diffuse irradiances
for blue light hazard under four different atmospheric conditions (solar height, h and cloudiness).
Device (Wm−2) Irradiance at 10 cm Irradiance at a Second Distance
Laptop 1 0.071 0.023
Smartphone 1 0.031 0.005
Smartphone 2 0.040 0.006
Smartphone 3 0.079 0.001
Smartphone 4 0.008 0.002
Smartphone 5 0.190 0.025
Tablet 1 0.234 0.037
Tablet 2 0.023 0.005
Tablet 3 0.069 0.014
Tablet 4 0.030 0.001
Sun (Wm−2) h = 70° (summer midday) h = 30° (winter midday)
Clear sky 25 18
Cloudy 35 14
Similarly, we integrated the solar diffuse spectra for blue light hazard in the same wavelength
range and found values between 18 to 25 Wm−2 for clear sky conditions and 14.5 and 35.5 Wm−2 for
simulations under cloudy conditions. The analysis of the blue light hazard for the simulated
radiances received from the opposite position of the Sun showed values ranging from 2.5 to 6.0 Wm−2
sr−1. As expected, the sky radiances in some directions were lower than the diffuse irradiances on a
horizontal surface due to the decrease in the solid angle. These values are similar to those presented
by O’Hagan et al. [19] for radiances in June and January; however, there are differences related to the
exact directions (height and azimuth angles) selected and the atmospheric conditions in both studies.
Okuno et al. [25] showed extremely high effective radiances for blue hazard when the detector was
pointed at the sun, confirming the danger of looking directly at the sun.
4. Discussion
The spectral irradiance—measured with a precise spectroradiometer—showed that the
emissions of the considered electronic devices were lower than those received from the sky on a
horizontal surface as a result of the multiple scattering of the solar beam with air molecules and
atmospheric aerosols throughout the atmosphere. Moreover, the simulated radiances at surface level
arriving from the sky—directly opposite the Sun’s position—were also lower than the emissions of
the electronic devices.
Due to the particular spectral emissions of these devices, the weighted irradiance for blue light
hazard ranged from 0.008 to 0.230 Wm−2. It is important to consider that the irradiances shown in this
study correspond to the emissions from blue screens on the electronic devices. In other conditions,
images combine the three primary colors, reducing the amount of blue light but increasing the
emissions at longer wavelengths, thus also contributing to eye hazards.
Energies 2020, 13, 4276 8 of 9
The observed differences between devices are related to the particular characteristics as well as
to the use of filters on the screens that reduce the blue light emission. These weighted irradiances are
lower than those estimated from solar spectra under clear and cloudy conditions. Our results agree
with other previous studies in which the emission of different electronic devices was measured and
evaluated regarding their potential blue light hazard [19,25].
Although the blue light emission of the measured devices did not show high values that should
be a cause for concern for eye diseases, these levels could influence circadian rhythms and sleep
quality [26,27]. These non-visual effects were beyond the scope of this study; nevertheless, more and
deeper analysis of the impact of low-level visible light on the human circadian system and possible
consequences for human health are necessary. Moreover, lightning regulations and practice continue
to focus on visual effects and energy efficiency, with little or no attention paid to their effects on the
intrinsically photosensitive retinal ganglion cells (ipRGCs) [28]. We would like to emphasize that it
is crucial that these future analyses should be based on precise spectral measurements of a large
number of different artificial sources to avoid unrealistic values and conclusions.
Author Contributions: Conceptualization, D.B.M.; methodology, D.B.M. and Y.S.; formal analysis, Y.S.;
resources, D.B.M.; writing—original draft preparation, Y.S.; writing—review and editing, D.B.M. and R.A.G.-L.;
supervision, R.A.G.-L. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments: The authors would like to acknowledge the kind participation of the volunteers who lent
their devices to be measured. The authors would also thank Jin for the maintenance of COART model.
Conflicts of Interest: The authors declare no conflict of interest.
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