The steep rise in personal electronics use and the transition from traditional incandescent lighting sources to compact fluorescent lights (CFL) and light-emitting diodes (LED) is dramatically increasing our exposure to blue light, raising new concerns about ocular health risks.

Blue light plays an important role in the body: it maintains circadian rhythms, improves alertness and can even be used in conjunction with photodynamic therapy to treat cancerous lesions; however, various types of blue light also pose hazards to our eyes and bodies.

As optometrists, we know that blue light is part of the visible spectrum of electromagnetic radiation. Visible light covers a range of electromagnetic wavelengths from approximately 380nm to 780nm. The blue-colored bands of light—known also as high-energy visible (HEV) light—are much more energetic than their longer wavelength counterparts.1 Blue light has been found to penetrate deeper into the eye than other wavelengths of light, and thus has the potential to cause changes in retinal tissues, including the macula. 

The prevailing wisdom concerning how light can impact human health has matured in recent decades, and continues to evolve as new technologies and research techniques are developed. Early research centered on the hormone melatonin, which is produced by the pineal gland from the amino acid tryptophan, and from the tryptophan-based neurotransmitter serotonin. Melatonin was first isolated from the bovine pineal gland in 1958, confirming the pineal gland as one of the regulatory centers for circadian rhythms in humans. Melatonin is secreted by the pineal gland in the presence of darkness with peak levels during the hours of 3am to 4am. It is at this time that the human body is most likely to sleep.2,3

Sleep Cycle Disruption

Blue light exposure at night has been shown to affect the quality of sleep. Researchers recently tested the effects of using e-readers prior to sleep for four hours vs. reading from a traditional book for four hours before sleep each night. The study found three notable results: 

  • Exposure to e-readers caused a 10-minute delay in sleep onset vs. the control group.
  • The experimental group spent less time in rapid eye movement (REM) sleep (109.04 ± 26.25 min vs. 120.86 ± 25.32 min in the print-book condition).
  •  There was a significant difference between groups in subjective feelings of tiredness and alertness the following morning.4 

The researchers attribute the difference to decreased time spent in REM sleep, given its importance in learning and storing memories.5 

These findings are concerning, given the behavior of our teenagers and young adults, who tend to spend their leisure time using digital devices in the evening prior to bedtime (and indeed all throughout the day). Concerns already exist that we have a sleep epidemic in the United States—people receive fewer hours of sleep at night than in the past and significantly less than the recommended amounts. Couple this with reduced sleep from electronic use prior to bedtime, and its resulting next-morning lethargy and lack of alertness, and we are at risk for having an underproductive, fatigued population prone to motor vehicle accidents and errors on the job and in school.

Impact on Refraction 

With the push for higher energy efficiency and cost savings in our schools, many school districts are now switching their lighting to LED-based lighting systems. While this may be good for school budgets, it is a detriment to children’s vision.  LED-based lighting, even the LED lights that emit a whiter rather than blue light, emit a significantly greater amount of blue light than traditional fluorescent lights used in classrooms. The change to LED-based lighting, coupled with the frequent use of computers by our students in the classroom, is cause for significant concern. Blue light has been shown to cause significant overaccommodation in students. Researchers found that when exposed to wavelengths below 430nm, rather than having the typical 0.3D lag of accommodation when focusing on a near target, students experience 1.0D of overaccommodation on average, or 1.3D sum total accommodative change from the normal posture for focusing at near. Additionally, this overaccomodation can cause distance blur as well.6 These accommodative changes are constant even in decreased luminance. The overaccommodation, mediated by the parafovea, appears to be caused by the absence of short-wavelength sensitive cones in the central fovea.6 This mechanism is also thought to trigger night myopia and is a potential driver of the myopic shift seen in our population in recent years.

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For our students, this classroom LED lighting change is being found to cause asthenopia and distance blur. As standardized testing and student performance is of major concern in our schools, this gives us as optometrists the potential to intervene with this lighting change by proactively meeting with school superintendents to recommend retaining traditional fluorescent lights in the classrooms until blue-light filtered LED systems are developed, reserving the installation of LED lights for areas only where student focusing needs are not required, such as in the hallways and cafeteria.While some lighting specialists are promoting the use of LED lights in the classroom to help reset student circadian rhythms for early start times and to improve student alertness, only lighting in the 444nm to 486nm wavelengths has been shown to impact the circadian rhythm, with peak sensitivity at 459nm to 464nm.7 By switching school lighting systems to LED lights, students are being exposed to all of the blue wavelengths of light for the entire school day, including the problematic wavelengths below 455nm. If schools wish to improve student alertness with lighting, research needs to be conducted to determine the appropriate duration and time of day students should be exposed to the 455nm to 486nm bandwidth, before such measures are put into place. A better idea: resolve to set later start times for middle and high schools to naturally align with student circadian rhythms—as the American Academy of Pediatrics has recently proposed.14

Most optometrists are already aware of the impact of blue light on the different tissues and structures in the eye. In 2004, researchers found evidence suggesting the impact of blue light exposure on the risk of macular degeneration in the retina.18 This led to subsequent studies on the long-term effects of visible light on the eye. In 2013, researchers identified the most damaging visible wavelengths to be in the blue-violet range of 415nm to 455nm. These wavelengths were found to be the most harmful to cells in the eye, as they can penetrate deeper into the eye and harm the retina, particularly the retinal pigment epithelium, causing the development of a toxic, apoptosis-causing molecule called N-retinlyidene-N-retinylethanolamine (A2E) to be produced within the RPE cells, causing cell viability loss.19,20

Does Blue Light Complicate Cancer Therapy?   

One of the newest studies supporting the theory of blue light impacting human health builds upon and synthesizes the research regarding the anti-oncogenic properties of melatonin with the impact of blue light on circadian rhythms and tissues in the human body. In 2014, researchers found that light exposure at night (LEN) suppresses melatonin production, and that altering light/dark cycles with dim LEN speeds the development of breast tumors and leads to tamoxifen resistance.21 They concluded that dim light exposure at night disturbs melatonin production and can render tumors insensitive to tamoxifen.21

The Role of the Pineal Gland 

For many years, researchers suspected that the suprachiasmic nucleus (SCN) of the hypothalamus was a primary regulatory center for the circadian rhythm after discovering that its removal led to a total disruption of the cycle.With the development of new gene analysis techniques in the early 2000s, a large number of receptors for melatonin were located in the SCN, confirming the SCN’s role in the circadian rhythm cycle.9 However, it wasn’t until 2002 that a new type of retinal photoreceptor—the intrinsically photosensitive retinal ganglion cell (ipRGC)—was identified as the primary mediator of the circadian rhythm pathway within the SCN of the hypothalamus.10,11 Researchers discovered that a photopigment called melanophore in the ipRGCs is involved in the neuronal relay process to the hypothalamus. These melanophores provided a concrete link between the circadian rhythm system of the hypothalamus and the retinal ganglion cells—identified as early as 1923.12 

More recently, scientists have come to view the pineal gland, via its secretion of melatonin, as the primary source of antioxidant activity. In 1993 melatonin was first identified as a free radical scavenger using the modern, oxygen-radical absorbance capacity assay technique.13 Evidence shows that melatonin directly scavenges free radicals (OH, H2O and single-oxygen molecules) in vitro and inhibits lipid peroxidation. Melatonin also stimulates a number of antioxidative enzymes.9 Melatonin has been shown to increase the efficiency of the electron transport chain and, as a consequence, to reduce electron leakage and the generation of free radicals, as well as to stabilize microsomal membranes, thus resisting oxidative damage.14,15 

The pineal gland has also been shown to have an anti-oncogenic, tumor-suppressing role in the body. A link exists between the pineal gland and cancer, a mutual and dynamic interaction between the secretion of melatonin and malignant growth.16 A fresh tumor is ‘sensed’ by the pineal gland via neuroimmunoendocrine changes, leading to a stimulation of melatonin secretion, which in turn activates endogenous defense processes. At this stage of cancer development, melatonin can exert a direct tumor-inhibitory activity.17 While melatonin has not been found to suppress advanced tumor growth (its tumor suppressing effects are seen primarily with early tumor growth), even in more advanced stages of cancer, melatonin has been found to improve quality of life with longer survival times.14 “The research suggests the effect of melatonin is due to its ability to induce sleep as well as positively affecting pain by interacting with the endorphin system.17

As optometrists routinely follow patients being treated with tamoxifen on a semi-annual or annual basis because of the potential for tamoxifen retinopathy, we are in a unique position to discuss the health risks of nighttime light exposure with these patients. I contacted the researchers of the study to see if they had looked at the impact of blue light at night vs. other wavelengths, to which Dr. Steven Hill, one of the researchers, replied that they are in the process of conducting such a study right now and that he will keep me apprised of their results. “Although we have not yet published work regarding blue and green wavelength light, we are well aware of their potent melatonin suppressive actions,” Dr. Hill stated. “Thus, we believe those using computers, cell phones, and televisions at night will have a 1.5 to 2-hour delay in their nighttime rise in melatonin after going to bed in the dark, and this will have an important negative impact on their breast cancer or other malignancies.”22 

While the blue wavelengths of 415nm to 455nm were found to be damaging to the retina, the wavelengths between 450nm to 550nm provide the strongest stimulation of circadian and neuroendocrine responses.1,23 As practitioners, we need to keep up to date on the latest studies reflecting the effects of light on our patients’ health, and we need to educate our patients on the risks of not only the blue light in the 415nm to 455nm band, but also those wavelengths in the 450nm to 550nm band as well.

Breast cancer is a major public health concern worldwide, and identifying an easily modifiable contributor to its development and successful treatment is of enormous consequence. What is remarkable about this study is that it runs counter to the prevailing assumption that a little bit of light at night is fine. How many of us grew up with a nightlight in our bedroom? Most of the public has heard bits and pieces about how being on the computer late at night disrupts our sleep cycle, but not much attention has been given to the risks of any light at all during nighttime. We need to take particular care to address this issue with our patients actively undergoing cancer treatment as well as those patients that are in remission, particularly with patients on tamoxifen adjuvant therapy. 

We should specifically point out to patients unrecognized sources of blue light. We need to educate all our patients regarding the risks of blue light from electronics as well as light exposure at night. As our patients (particularly our school-age and young adult patients) become more and more dependent on their use of computers in all walks of life, they are exposed to more blue light than any generation before. It is vital to consider the potential hazards of such exposure and to educate our patients about its risks, including the loss of antioxidant and anticancer functioning, disruption to the circadian rhythm and sleep cycle, and potential vision loss from AMD. 

Researchers will continue refining the blue light theory and developing ways to protect the eyes through optical lenses, changes to the lighting sources for computer monitors, software that reduces blue light emissions from computer screens and through general public health education. As new hazards emerge and evolve, it is our responsibility to update our education and interventional efforts. 

Dr. Heather Flint Ford works in private practice at Clear Choice EyeCare, in Pottstown, Pa. She is a recipient of the Future Stem Teachers of America Scholarship, a scholarship designed to bring industry professionals into the classroom. She is currently completing a program through Western Governors University to receive her teaching certification in Middle School Science.

1. Smick K et al. Blue light hazard: new knowledge, new approaches to maintaining ocular health. Report of roundtable sponsored by Essilor of America in NYC, NY. 2013, March 16.

2. Lerner A, Case J, Takahashi Y et al. Isolation of melatonin, the pineal gland factor that lightens melanocytes. J Amer Chem Soc. 1958;80:2587-92.

3. Khullar A. The role of melatonin in the circadian rhythm sleep-wake cycle. Psychiatric Times online. 2012, July 9.

4. Lissoni P, Barni S, Ardizzoia A et al. A randomized study with the pineal hormone melatonin versus supportive care alone in patients with brain metastases due to solid neoplasms. Cancer. 1994;(73):699–701. 

5. Chang A, Aeschbach D, Duffy J, Czeisler C. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 2015 Jan 27;112(4):1232-37.

6. Graef K and Schaeffel, F.  Control of accommodation by longitudinal chromatic aberration and blue cones.  J of Vis. 2012;12(1):14. 

7. Hanifin J, Brainard G. Photoreception for circadian, neuroendocrine, and neurobehavioral regulation. J Phys Anthro. 2007;26(2);87-94.

8. Abe K, Kroning J, Greer M, Critchlow V. Effects of destruction of the suprachiasmatic nuclei on the circadian rhythms in plasma corticosterone, body temperature, feeding and plasma thyrotropin. Neuroendocrinology. 1979;29(2):119-31.

9. Anisimov V, Popovich I, Zabezhinski M, et al. Melatonin as antioxidant, geroprotector and anticarcinogen. Biochimica et Biophysica Acta. 2006;1757:573–89.

10. Hattar S, Liao H, Takao M, et al. Melanopsin containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science. 2002 Feb 8; 295(5557):1065-70.

11. Wong K, Dunn F, Berson D. Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells. Neuron. 2005 Dec 22;48(6):1001-10.

12. Zimmer C. Our strange, important, subconscious light detectors. Discover Magazine. 2012 Feb. Retrieved online:

13. Hanifin J, Brainard G. Photoreception for circadian, neuroendocrine, and neurobehavioral regulation. J Phys Anthro. 2007;26(2);87-94.

14. American Academy of Pediatrics. Policy statement: school start times for adolescents. Pediatrics. Sept 2014;134(3).

15. Tan D, Chen L, Poeggeler B, et al. Melatonin: a potent, endogenous hydroxyl radical scavenger. Endocr. J. 1993;1:57–60.

16. Bartsch C, Bartsch H. Pineal gland and cancer—an epigenetic approach to the control of malignancy: evaluation of the role of melatonin. Madame Curie Bioscience Database [Internet]. 2000; Austin, TX: Landes Bioscience. Available from:

17. Qi W, Reiter R, Tan D, et al. Increased level of oxidatively damaged DNA induced by chromium (III) and H2O2: protection by melatonin and related molecules. J Pineal Res 2001;29:54–61.

18. Karbownik M, Garcia J, Lewinski A, Reiter R. Carcinogen-induced, free radical-mediated reduction in microsomal membrane fluidity: reversal by indole-3-propionic acid. J. Bioenerg. Biomembr. 2001;33:73–8.

19. Dillon J, Zheng L, Merriam JC, Gaillard ER. Transmission of light to the aging human retina: possible implications for age related macular degeneration. Exp Eye Res. 2004 Dec;79(6):753-9.

20. Arnault E, Barrau C, Nanteau C, et al. Phototoxic action spectrum on a retinal pigment epithelium model of age-related macular degeneration exposed to sunlight normalized conditions. PLoS ONE. 2013;8(8):1-12.

21. Dauchy R, Xiang S, Mao L, et al. Circadian and melatonin disruption by exposure to light at night drives intrinsic resistance to tamoxifen therapy in breast cancer. Cancer  Research. 2014 Aug 1;74(15). Retrieved from on April 19, 2015.

22. Hill, Steven and Ford, Heather – direct e-mail correspondence 3/24/15 - 3/26/15.

23.Hanifin J, Brainard G. Photoreception for circadian, neuroendocrine, and neurobehavioral regulation. J Phys Anthro. 2007 26(2):87-94.