ORIGINAL CLINICAL STUDY
Effect of Blue LightYReducing Eye Glasses
on Critical Flicker Frequency
Takeshi Ide, MD, PhD,*Þ Ikuko Toda, MD,*Þ Emiko Miki, MD,* and Kazuo Tsubota, MDÞ
Purpose: This study aims to evaluate the effect of blocking shortwavelength light on critical flicker frequency (CFF).
Design: This study is a prospective clinical study.
Methods: Thirty-three participants (17 men and 16 women; age range,
28Y39 years) were divided into 3 groups. Each group wore 1 of 3 types
of lenses while performing an intensive computer task for 2 hours. To
evaluate the effect of blocking short-wavelength light before and after
the task, we measured the CFF and evaluated subjective questionnaires.
We used the analysis of variance test to examine whether the type of
lenses tested affected any of the visual fatigue-related parameters.
Results: The type of lens worn significantly affected the CFF; however, answers to the subjective questionnaires did not differ significantly
between the groups. Two of the 13 question items showed a statistical
difference between lens transparency and increase in the CFF (lens 3 9
lens 2 9 lens 1).
Conclusions: The higher the blocking effect of the lens, the lower the
reduction in the CFF, suggesting that blocking short-wavelength light
can reduce eye fatigue.
Key Words: eye fatigue, blue light, VDT, CVS, critical flicker
frequency
(Asia Pac J Ophthalmol 2015;4: 80Y85)
I
n association with advances in computer technology, human
reliance on computers to execute work-related tasks has increased immensely.1 In the past, these tasks were performed via
a man-machine interface using traditional hardware equipment
such as meters, dials, and monochrome televisions. However,
since computers have replaced the man-machine interface, the
scope of these work-related tasks and the time taken to perform
them has changed, and newer-generation monitors are being
employed for mainstream use. Notably, the use of computers
at work has been found to contribute to occupational stress.2
As one would expect, visual and musculoskeletal disorders are
highly prevalent in visual display terminal (VDT) users.3Y5
Computer vision syndrome (CVS) refers to a complex of
eye and vision conditions related to the use of computers.
Computer vision syndrome is characterized by visual symptoms
caused by exposure to VDTs or their environment. Most studies
indicate that visual symptoms occur in 50% to 90% of VDT
users. One study conducted by the National Institute of Occupational Safety and Health showed that 22% of VDT users have
From the *Minamiaoyama Eye Clinic; and †Department of Ophthalmology,
Keio University School of Medicine, Tokyo, Japan.
Received for publication May 8, 2013; accepted May 25, 2014.
The glass frames and lenses were provided by JIN Co, Ltd (Tokyo, Japan).
The authors have no funding or conflicts of interest to declare.
Reprints: Takeshi Ide, MD, PhD, Minamiaoyama Eye Clinic, Renai Aoyama
Building, 4F, 3-3-11, Kitaaoyama, Minato-ku, Tokyo 107-0061, Japan.
E-mail: [email protected].
Copyright * 2014 by Asia Pacific Academy of Ophthalmology
ISSN: 2162-0989
DOI: 10.1097/APO.0000000000000069
80
www.apjo.org
musculoskeletal disorders. Vision problems are currently pervasive among computer workers and are the primary source of
worker discomfort and decreased work performance.6
Currently, a majority of computer screens are liquid crystal displays (LCDs). Liquid crystal displays emit more blue
light than the previous-generation cathode ray tubes. In addition, we are surrounded by more fluorescent light and lightemitting diodes than before. These lighting instruments also
emit more short-wavelength light than the incandescent lamps
used previously.
Compared with green light of the same intensity, blue light
has been shown to have a greater effect on various physiological
factors such as melatonin suppression, alertness, thermoregulation, heart rate, cognitive performance, and electroencephalographic dynamics.7,8 Blue light is considered to be 1 of the causes
of eye strain.9
Retinal rod and cone photoreceptors transmit conscious
visual information through retinal ganglion cells and lateral
geniculate nuclei to the visual cortex. For more than 100 years,
those who used these lights have often found that their sense
of brightness does not match the values measured by light meters. Areas lit by lighting that has a bluish tint appear brighter
than the same areas lit by lighting with a more orange or reddish tint, even though a light meter may indicate the opposite.
The 6 to 7 million cones that mediate the eye’s color sensitivity can be divided into red cones (64%), green cones (32%),
and blue cones (2%), based on the measured response curves.
However, the blue sensitivity of our final visual perception is
at least comparable (and may be even better) to the red and
green sensitivities, suggesting the presence of a somewhat selective ‘‘blue amplifier’’ in the visual processing system of
the brain.
Furthermore, the light response of the rods peaks sharply
in blue light; they respond poorly to red light. Rod sensitivity is
shifted toward shorter wavelengths (507 nm) as compared with
cone sensitivity.10
In 2002, a subset of retinal ganglion cells (G1% in humans)
was found to function as photoreceptors.11 These photosensitive retinal ganglion cells (pRGCs), which express the blue
lightYsensitive photopigment melanopsin, transmit information via the retinal hypothalamic tract. The cells synapse directly on neurons in the suprachiasmatic nuclei and other
nonvisual brain centers.12 Approximately 3000 pRGCs make
up a light-sensitive network that spans the retina. Peak absorption by isolated pRGCs and melanopsin is noted at 480 nm.11
Therefore, the nonvisual effects produced through exposure to
light are greater when the wavelengths are shorter than when
the light is geared toward daytime vision.13 The nonvisual effects associated with pRGCs include physiological responses
such as the suppression of melatonin,14 circadian phase shifting,15 the elevation of core body temperature,16 and an increase
in heart rate.17 Furthermore, exposure to polychromatic white
light elicits behavioral responses including enhanced alertness
and performance18Y20 and improved brain responses to cognitive tasks, as detected by photon emission tomography21 and
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Asia-Pacific Journal of Ophthalmology
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Volume 4, Number 2, March/April 2015
functional magnetic resonance imaging,22 when compared with
the effects of green light of the same intensity.7,8 These findings
show that the visual and nonvisual effects of short-wavelength
light may affect eye fatigue.
The flicker fusion threshold is lower for a fatigued observer. Decrease in the critical fusion frequency (CFF) has often
been used as an index of central fatigue.23,24 The ability to
perceive flicker depends strongly on the light intensity and the
wavelength of the stimulating light.25,26
In response to this research, several types of computer
glasses have been designed to block short-wavelength light, relax ocular muscles, decrease eye strain, enhance contrast, reduce glare, and increase visual endurance and productivity. In
this study, we investigated the effect of computer glasses on CFF,
as an index of eye fatigue, after brief computer tasks.
MATERIALS AND METHODS
This study included 33 subjects (17 men and 16 women)
aged 28 to 39 years. The demographics of the study participants
recruited are summarized in Table 1. Each had a corrected visual acuity of 0.7 or better and normal color vision. The study
population was divided into 3 groups depending on the type of
glasses worn during the study; these are as follows: blue light
filtering lenses (lens 1, high blocking rate), blue light filtering
lenses (lens 2, low blocking rate), or transparent lenses (lens 3,
control). The blue light filtering lenses were cut to filter light
with a wavelength of 380 to 500 nm. The lenses were evaluated
based on the British Standard Specification for sun glare eye
protectors for general use (BS 2724: 1987). The associated data
are shown in Table 2 and Figure 1. The protocol for this experimental study was approved by the institutional review board
at Minamiaoyama Eye Clinic.
The participants worked on the computer for 2 hours,
performing tasks that required constant attention, using ChipClick
software (http://www.vector.co.jp/soft/win95/game/se262423.html).
Subject performance was evaluated using the Advanced TrailMaking Test method27; the subjects examined sequences of
numbers that appeared randomly on the screen and clicked on the
numbers in numerical order. An Intel Core i5Y430 M 2.53 GHz
laptop computer with a 15.5 (16:9) TFT LCD monitor was used
for the study (VAIO VPCEB2AGJ; Sony, Tokyo, Japan). The
screen display was set to the maximum brightness setting. Room
luminance was approximately 800 to 900 lux.
The participants wore 1 of the 3 types of lenses (lens 1, 2,
or 3, as described above) with the same glass frame. Because
the participants had normal vision and did not wear glasses regularly, they were requested to wear the same glasses that were
used for the control group (lens 3) for a 2-week period leading up
to the experiment.
Before and after the experimental tasks were conducted,
visual fatigue was assessed by calculating the CFF and by
evaluating the answers to a questionnaire on visual complaints.
The CFF value was measured using a Handy Flicker HF-II
TABLE 1. Demographics of the Study Participants
Lens
Lens 1 High blocking
Lens 2 Low blocking
Lens 3
Control
Age
Sex, Sex,
Age Range, y (Mean T SD) M
F
28Y34
30Y39
28Y38
31.36 T 2.01
33.36 T 2.2
34.64 T 3.32
SEX M indicates male; SEX F, female.
* 2014 Asia Pacific Academy of Ophthalmology
3
7
7
8
4
4
Effects of Blue Light on CFF
TABLE 2. The Characteristics of the Lenses Used in
the Experiments
Lens 1
Lens 2
Lens 3
Lens
Blue Range Cut, %
High blocking
Low blocking
Control
53.9
35.1
26.1
(Neitz Instrument, Tokyo, Japan). The mean CFF of 3 trials
was recorded.
The 13-item questionnaire is shown in Table 3 (2 items
with simple yes or no answers and 11 items with scale-based
answers). A 5-point scale was used, with 1 representing ‘‘not at
all’’ and 5 representing ‘‘yes, very much.’’
The dependent variables were CFF and scores on the subjective questionnaire. The independent variables were the types
of glass lenses. To examine the effects of the independent variables, the data were analyzed using SPSS ver 18 (SPSS Inc,
Chicago, Ill). P G 0.05 was considered to indicate statistical
significance.
RESULTS
On analyzing the within-group differences in preexperiment and postexperiment CFF results, a statistically significant
decrease in CFF was found in the lens 3 (control) group,
whereas no significant decreases were observed in the lens 1
and lens 2 groups (Fig. 2).
DISCUSSION
In this study, we focused on the effects of blocking shortwavelength light on CFF, which has been said to be related to
eye strain/fatigue. Subjects performed 2-hour tasks on the computer while wearing 1 of the 3 types of lenses. These tasks
required continuous attention. The lenses differed primarily in
terms of their ability to block short-wavelength light. Various
methods have been used to measure eye fatigue, including the
CFF, visual acuity, subjective ratings of visual fatigue, accommodation power, pupil diameter, eye movement velocity, and
task performance.28 Among these methods, CFF, visual acuity,
and subjective ratings of visual fatigue have been used most extensively for the measurement of visual strain in tasks involving
TABLE 3. Thirteen Questions in the Questionnaire
Yes/No Questions
Dry eyes
Irritated eyes
Scale-based questions (1-5)
Difficulty in refocusing the eyes
Polyopia/double vision/blurred vision
Photophobia (when outdoors)
Photophobia (when staring at the computer monitor)
Itchy eyes
Eye strain/fatigue
General fatigue
Mental stress
Sleepiness when working
Neck/shoulder/back/waist pain
Finger pain
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Asia-Pacific Journal of Ophthalmology
Ide et al
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Volume 4, Number 2, March/April 2015
FIGURE 1. Lens spectra. The spectra of the lenses were analyzed based on the British Standard Specification for sun glare eye protectors
for general use (BS 2724: 1987). The major difference was the cut rate for short-wavelength light. A, lens 1 (high cut rate), (B) lens 2
(low cut rate), and (C) lens 3 (control lens).
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Asia-Pacific Journal of Ophthalmology
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Volume 4, Number 2, March/April 2015
FIGURE 2. Changes in the CFF. In the lens 3 group, CFF
decreased significantly after the examination. The decrease in
CFF was statistically significant in lens 3, when compared with
that of the lens 1 and lens 2 groups, whereas no significant
difference between the lens 1 and lens 2 groups was noted. The
Tukey HSD (honestly significant difference) method was
used for statistical analysis.
VDTs.29Y32 We therefore chose to examine CFF and subjective
questionnaire responses. The results of our study showed that the
type of lenses tested affected the CFF (Fig. 2) but not subjective answers to the questionnaire. Nevertheless, the answers to
2 of the 13 items suggested that the cut rate may partly explain
the observed reductions in eye fatigue (Fig. 3). Other studies
have established that reductions in CFF are positively correlated
with the duration of VDT use.33Y35 In this study, a significant
difference was observed in the CFF values measured in the lens
1 and lens 2 groups after 2-hour computer tasks. We found that
the greater the reduction in the transmission of short-wavelength
light, the lower was the reduction in CFF values.
Numerous studies have reported that good lighting contributes to improved work performance and decreased accident
rates.36Y38 Juslén et al39 also found that increased industrial
lighting intensities lead to increased productivity. Bommel et al40
showed that increasing the lighting intensity from the minimum 300 to 500 lux leads to an increase of more than 8% in
productivity. Offices typically use bright fluorescent lights, lightemitting diode lights, and LCD monitors, which are bright and
emit more bluish light than incandescent lamps and cathode ray
tubes. On the other hand, bright light has been found to cause
ocular discomfort and/or pain. Okamoto et al41 identified a novel
reflex circuit necessary for bright light to excite nociceptive
neurons in the superficial laminae of the trigeminal subnucleus
caudalis (Vc/C1). These findings support the hypothesis that
bright light activates trigeminal nerve activity through an intraocular mechanism driven by a luminance-responsive circuit and
increased parasympathetic outflow to the eye.41
Viola et al42 showed that blue-enriched white lighting in offices
has beneficial effects on daytime alertness, performance, mood, and
eye strain, as well as on nighttime sleep quality and duration.35,43
The precise effect of wavelength on the judgment of CFF
has been a controversial issue for many years. Giorgi25 performed a systematic investigation in which the intensity of
the light source was controlled by means of neutral tint filters
and an optical wedge. Eight wavelengths covering most of the
visible spectrum were used, and the CFF thresholds were obtained at 7 different luminance levels for each wavelength. On
the basis of their results, the authors suggested that the wavelengths at the opposite ends of the spectrum are the ones that
show a greater degree of difference. The wavelengths in the
middle regions of the spectrum, as a rule, are not significantly
* 2014 Asia Pacific Academy of Ophthalmology
Effects of Blue Light on CFF
different from the extremes or from other wavelengths in the same
region. Apparently, the greater separation between the wavelengths
is the probability of significance. The flicker instrument we used
(Handy Flicker HF-II; Neitz Instrument, Tokyo, Japan) has 3 light
sources (yellow, green, and red), and we used the yellow light
source, which has been used for fatigue evaluation. The yellow
wavelength is not at the extreme end of the visible light spectrum.
This study only recruited participants who worked during
normal office hours (8:30 AM to 4:45 PM).42 In reality, however,
many people work overtime under blue-enriched light for a
longer duration during the day and even late at night.42,44
With regard to age, increased illumination has been shown
to improve rest-activity rhythms in the elderly population45 and
in those with dementia.46 Interestingly, the magnitude of the
increase in melatonin secretion in the elderly population paralleled the improvement in sleep.45
Exposure to blue-enriched white light may also lead to
stronger pupil constriction than would standard white light,
which in turn may contribute to the improvements in visual
comfort that are noted with blue-enriched white light.47 However, some researchers suggest that blue-blocking intraocular
chromophores do not reduce clinical disability glare because
they decrease target luminance in the same proportion as does
veiling stray light.48 Furthermore, they do not significantly improve contrast sensitivity because contrast transfer at mid-to-high
FIGURE 3. Questionnaire trend. The questionnaire consisted
of 13 items. Two types of visual complaints (A, neck/shoulder/
back/waist pain; B, eye strain/fatigue) were less severe when less
blue light was transmitted.
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Asia-Pacific Journal of Ophthalmology
Ide et al
spatial frequencies occurs at wavelengths between 500 and
600 nm, which are essentially unaffected by yellow chromophores.48 In addition, light stimuli around 470 nm are thought to
trigger migraines.49
Our study results may make readers think that blue light
causes only hazardous effects, but this is not our point. Both
basic and clinical investigations suggested that we have to get
along with lights properly in terms of quality and quantity. From
clinical standpoints, blue light or shorter wavelength light is
broadly used in phototherapy for neonatal jaundice, depression,
skin problem, depression, sleep problem, and so on.
This study has several limitations such as the small sample size and the low representativeness of the sample, which
gives results that may not be representative of the general population. The experimental conditions were very different from
the actual working conditions. This study involved 2-hour-long
attention-intensive tasks performed using a bright monitor.
The demographics of the 3 groups were relatively comparable;
however, each participant may have been exposed to a different
work environment in his or her daily life. Although a few
workers may have been accustomed to severe VDT conditions,
others may not have been. In addition, the age range of the
participants was broad (11 years). Age affects accommodation,
pupil constriction, light transmittance, and so on. In the young
eye, ocular transmittance is very high, reaching close to 90%
at 450 nm. The transmittance in elderly lenses is much lower;
it shows considerable interindividual variation and generally
does not reach 70% to 80% until wavelengths of 540 nm.50
Another limitation is that indoor lighting provides at best 5%
of natural light intensity,51,52 and its longer (redder) wavelength spectra are less efficient for pRGC photoreception.49
Some have claimed that unconscious pRGC photoreception
requires much higher light intensities than those needed for
conscious vision.11,12,53
Therefore, to address these limitations, more data must
be accumulated in future studies using a larger, strictly agematched population under conditions that more closely simulate real life. We performed this study using several glass lenses,
but of course, lens change is not the only option for eye strain
relief. Eye fatigue is multifactorial and is a part of CVS. This
CVS can be reduced by repositioning the monitor (eg, tilt, gaze
position); adjusting color, brightness, and contrast; or by using
a low-glare monitor/filter, screen hood, and/or lighting reflecting
on the monitor.35,54,55
Because many individuals have CVS, the subjective and
objective reductions in eyestrain, mental stress, and musculoskeletal pain achieved through the use of light-blocking computer glasses are worth the associated costs.
REFERENCES
1. Wang AH, Tseng CC, Jeng SC. Effects of bending curvature and
text/background color-combinations of e-paper on subjects’ visual
performance and subjective preferences under various ambient
illuminance conditions. Displays. 2007;28:161Y166.
2. Smith MJ, Conway FT, Karsh BT. Occupational stress in human
computer interaction. Ind Health. 1999;37:157Y173.
3. Berqvist U. Video display terminals and health. Scand J Work Environ
Health. 1984;10(Suppl 2):1Y87.
&
Volume 4, Number 2, March/April 2015
6. Computer Vision Syndrome (CVS) America Optometrist
Association Web site. Available at: http://www.aoa.org/optometrists/
tools-and-resources/clinical-care-publications/
environmentaloccupational-vision/computer-use-needs/
computer-vision-syndrome-symptoms. Accessed April 13, 2014.
7. Lockley SW, Evans EE, Scheer FA, et al. Short-wavelength sensitivity
for the direct effects of light on alertness, vigilance, and the waking
electroencephalogram in humans. Sleep. 2006;29:161Y168.
8. Cajochen C, Munch M, Kobialka S, et al. High sensitivity of human
melatonin, alertness, thermoregulation, and heart rate to short
wavelength light. J Clin Endocrinol Metab. 2005;90:1311Y1316.
9. Wilkins AJ, Wilkinson P. A tint to reduce eye-strain from fluorescent
lighting? Preliminary observations. Ophthalmic Physiol Opt.
1991;11:172Y175.
10. Paget L, Scott A, Bräuer R, et al. Why Is Blue Tinted Backlight Better?
Available at: http://www.eizo.eu/html_76/ftp/
article_bluetintedbacklight.pdf. Accessed January 27, 2014.
11. Berson DM, Dunn FA, Takao M. Photo transduction by retinal ganglion
cells that set the circadian clock. Science. 2002;295:1070Y1073.
12. Hannibal J, Fahrenkrug J. Neuronal input pathways to the brain’s
biological clock and their functional significance. Adv Anat Embryol
Cell Biol. 2006;182:1Y71.
13. Brainard GC, Hanifin JP, Greeson JM, et al. Action spectrum for
melatonin regulation in humans: evidence for a novel circadian
photoreceptor. J Neurosci. 2001;21:6405Y6412.
14. Lewy AJ, Wehr TA, Goodwin FK, et al. Light suppresses melatonin
secretion in humans. Science. 1980;210:1267Y1269.
15. Czeisler CA, Allan JS, Strogatz SH, et al. Bright light resets the
human circadian pacemaker independent of the timing of the
sleep-wake cycle. Science. 1986;233:667Y671.
16. Dijk DJ, Cajochen C, Borbely AA. Effect of a single 3-hour exposure
to bright light on core body temperature and sleep in humans.
Neurosci Lett. 1991;121:59Y62.
17. Burgess HJ, Sletten T, Savic N, et al. Effects of bright light and
melatonin on sleep propensity, temperature, and cardiac activity at
night. J Appl Physiol. 2001;91:1214Y1222.
18. Campbell SS, Dawson D. Enhancement of nighttime alertness and
performance with bright ambient light. Physiol Behav.
1990;48:317Y320.
19. Campbell SS, Dijk DJ, Boulos Z, et al. Light treatment for sleep
disorders: consensus report, III: alerting and activating effects.
J Biol Rhythms. 1995;10:129Y132.
20. Cajochen C, Zeitzer JM, Czeisler CA, et al. Dose-response
relationship for light intensity and ocular and electroencephalographic
correlates of human alertness. Behav Brain Res. 2000;115:75Y83.
21. Perrin F, Peigneux P, Fuchs S, et al. Nonvisual responses to light
exposure in the human brain during the circadian night. Curr Biol.
2004;14:1842Y1846.
22. Vandewalle G, Balteau E, Phillips C, et al. Daytime light exposure
dynamically enhances brain responses. Curr Biol. 2006;16:1616Y1621.
23. The Effect of Blue Light on Visual Fatigue When Reading on
LED-backlit Tablet LCDs. Available at: http://web.iiit.ac.in/
~apurva.kumar/files/publications/BlueLightFatigue.pdf. Accessed
January 27, 2014.
24. Simonson E, Enzer N. Measurement of fusion frequency of flicker as
a test for fatigue of the central nervous system. J Indus Hyg Tox.
1941;24:83Y89.
4. Bergqvist U, Knave BG. Eye discomfort and work with visual display
terminals. Scand J Work Environ Health. 1994;20:27Y33.
25. Giorgi A. Effect of wavelength on the relationship between critical
flicker frequency and intensity in foveal vision. J Opt Soc Am.
1963;53:480Y4846.
5. Carter JB, Banister EW. Musculoskeletal problems in VDT work: a
review. Ergonomics. 1994;37:1623Y1648.
26. Prescott NB, Wathes CM, Jarvis JR. Light, vision and the welfare
of poultry. Animal Welfare. 2003;12:269Y288.
84
www.apjo.org
* 2014 Asia Pacific Academy of Ophthalmology
Copyright © 2015 Asia Pacific Academy of Ophthalmology. Unauthorized reproduction of this article is prohibited.
Asia-Pacific Journal of Ophthalmology
&
Volume 4, Number 2, March/April 2015
Effects of Blue Light on CFF
27. Mizuno K, Tanaka M, Nozaki S, et al. Mental fatigue-induced
decrease in levels of several plasma amino acids. J Neural Transm.
2007;114:555Y561.
42. Viola AU, James LM, Schlangen LJ, et al. Blue-enriched white light
in the workplace improves self-reported alertness, performance and
sleep quality. Scand J Work Environ Health. 2008;34:297Y306.
28. Chi CF, Lin FT. A comparison of seven visual fatigue assessment
techniques in three data-acquisition VDT tasks. Hum Factors.
1998;40:577Y590.
43. Kinney JAS, Neri DF, Mercado DT, et al. Visual fatigue in sonar control
room lighted by red, white or blue illumination. Naval Submarine
Medical Research Laboratory, Report No. 1000. 1983.
29. Shieh KK. Effects of reflection and polarity on LCD viewing distance.
Int J Ind Ergon. 2000;25:275Y282.
44. Mills PR, Tomkins SC, Schlangen LJM. The effect of high correlated
colour temperature office lighting on employee wellbeing and work
performance. J Circadian Rhythms. 2007;5:2.
30. Murata K, Araki S, Yokoyama K, et al. Accumulation of VDT
work-related visual fatigue assessed by visual evoked potential, near
point distance and critical flicker fusion. Ind Health. 1996;34:61Y69.
31. Wilmshurst P. Making light with health and safety. Professional
Engineering. 1994;7:14Y15.
32. Tomei G, Rosati MV, Martini A, et al. Assessment of subjective stress
in video display terminal workers. Ind Health. 2006;44:291Y295.
33. Shieh KK, Chen MT. CFF and subjective visual fatigue as a function
of VDT task characteristics. The 4th Pan Pacific Conference on
Occupational Ergonomics, Ergonomics Society of Taiwan. 1996;
143Y146.
34. Nishiyama K. Ergonomic aspects of the health and safety of VDT
work in Japan: a review. Ergonomics. 1990;33:659Y685.
35. Lin CJ, Feng WY, Chao CJ, et al. Effects of VDT workstation lighting
conditions on operator visual workload. Ind Health. 2008;46:105Y111.
36. Wolska A. Visual strain and lighting preferences of VDT users under
different lighting systems. Int J Occup Saf Ergon. 2003;9:431Y440.
45. Mishima K, Okawa M, Shimizu T, et al. Diminished melatonin
secretion in the elderly caused by insufficient environmental
illumination. J Clin Endocrinol Metab. 2001;86:129Y134.
46. Van Someren EJ, Kessler A, Mirmiran M, et al. Indirect bright light
improves circadian rest-activity rhythm disturbances in demented
patients. Biol Psychiatry. 1997;41:955Y963.
47. Vandewalle G, Schmidt C, Albouy G, et al. Brain responses to violet,
blue, and green monochromatic light exposures in humans: prominent
role of blue light and the brainstem. PLoS One. 2007;2:e1247.
48. Mainster MA, Turner PL. Blue-blocking IOLs decrease photoreception
without providing significant photoprotection. Surv Ophthalmol.
2010;55:272Y289.
49. Noseda R, Kainz V, Jakubowski M, et al. A neural mechanism for
exacerbation of headache by light. Nat Neurosci. 2010;13:239Y245.
50. Algvere PV, Marshall J, Seregard S. Age-related maculopathy and
the impact of blue light hazard. Acta Ophthalmol Scand.
2006;84:4Y15.
37. Boyce PR. Lighting research for interiors: the beginning of the end
or the end of the beginning. Lighting Res Technol. 2004;36:283Y294.
51. Turner PL, Mainster MA. Circadian photoreception: aging and the
eye’s important role in systemic health. Br J Ophthalmol. 2008;92:
1439Y1444.
38. Küller R, Ballal S, Laike T, et al. The impact of light and colour on
psychological mood: a cross-cultural study of indoor work
environments. Ergonomics. 2006;49:1496Y1507.
52. Figueiro MG, Rea MS, Bullough JD. Does architectural lighting
contribute to breast cancer? J Carcinog. 2006;5:20.
39. Juslén H, Wouters M, Tenner A. The influence of controllable
task-lighting on productivity: a field study in a factory. Appl Ergon.
2007;38:39Y44.
53. Rea MS, Figueiro MG, Bullough JD, et al. A model of
phototransduction by the human circadian system. Brain Res Rev.
2005;50:213Y228.
40. van Bommel WJM, Van den Beld GJ. Industrial lighting, productivity,
health and well being. Journal of Lighting Engineering. 2001;3:5Y28.
54. United States Department of Labor. Occupational Safety & Health
Administration (OSHA). Available at: https://www.osha.gov/SLTC/
computerworkstation. Accessed on January 27, 2014.
41. Okamoto K, Tashiro A, Chang Z, et al. Bright light activates a
trigeminal nociceptive pathway. Pain. 2010;149:235Y242.
55. Maine Department of Labor. Available at: http://www.safetyworksmaine.com/
training/online_classes/vdt/vdt.pdf. Accessed January 27, 2014.
Success is a lousy teacher. It seduces smart people into thinking they can’t lose.
V Bill Gates
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