Multiple studies on the sources and effects of blue light have demonstrated ocular risk, but it may take more research over several more years to fully understand its impact.
With all the confusion surrounding this topic it’s helpful to understand some of the studies that indicate how blue light may be affecting the eyes.
The light spectrum contains many more wavelengths than humans can see. Frequencies of light include microwaves, radio waves and x-rays, to name a few. The visible spectrum is only a very thin portion of wavelengths between 380nm and 780nm. The highest energy of the visible spectrum is immediately adjacent to the UV spectrum and is just above 380nm (typically noted as 380nm to 460nm). This high energy blue light scatters in the atmosphere and is the reason why the sky appears blue. Blue light makes up 25-30% of daylight. 
Blue light is also produced by light-emitting diodes (LEDs). LED lighting is widely found in digital technologies such as televisions, smartphones and tablets. A 2016 report from The Vision Council found that 60% of Americans use digital devices for more than five hours each day, and 70% use at least two or more devices at one time. 
From an ocular health perspective, it has been long known that blue light is toxic to certain ocular structures. The longer the wavelength, the higher the proportion that passes through the cornea and reaches the lens and retina. On average, the human cornea absorbs wavelengths below 300nm, and the lens absorbs those below 400nm. Upon closer analysis, though, this changes throughout life as a clear crystalline lens at birth and in childhood years transmits light at 300nm+, whereas an adult (and a more yellow crystalline lens) transmits at 400nm+.
Protection of children’s eyes is especially important since transmittance is greatest at a younger age, allowing higher levels of UV and blue light to reach the lens and retina.  The retina is posed a risk as it absorbs light over 400nm.  Given that the spectrum of high-energy blue light is known to be 380nm to 460nm, there is a portion of blue light that is problematic. Ocular exposure to light around 435nm (+/- 20nm) can induce irreversible cell death in the retinal pigment epithelium (RPE). 
Historically, there have been several large-scale population studies that have demonstrated the ocular risk from blue light. The Chesapeake Bay Waterman Study had several iterations of meta-analysis, and an association was identified between cumulative blue light exposure and age-related macular degeneration (AMD).
Similarly, the Beaver Dam Eye Study concluded that exposure to bright visible light might be associated with AMD. Finally, the Visual Impairment Project suggested that individuals with more sunlight exposure are at a significantly increased risk for AMD.  As such, sunlight (and more specifically, cumulative blue light) has been identified as a risk factor for AMD. There is a specific photosensitive visual pigment that appears to be involved in this retinal toxicity, and it is referred to as A2E (N-retinylidene-N-retinylethanolamine).
A 2013 study defined the most toxic wavelengths of light in an in-vitro model. Their conclusion was that the most loss of retinal cell viability occurred between 415nm and 455nm.  What is additionally worrisome is that retinal cell death occurs via apoptosis (a continual cascade of death of neighboring cells) and is likely what makes AMD visually destructive. 
There does exist some confusion as to where the risk of ocular damage originates. It should be explained that the sun emits over 100 times the amount of blue light than digital devices or LEDs. Though we spend many hours per day on illuminated screens and computer technologies, it has been proposed that the blue light hazard from digital devices may not approach dangerous limits. 
What is known, though, is that digital device usage can wreak havoc on our sleep patterns by interfering with human circadian rhythms. In the absence of blue light, ganglion cells in the human retina stimulate the pineal gland of the brain to release melatonin, a hormone that lets our bodies know it is time for sleep. This is in stark contrast to the presence of blue light, which suppresses melatonin production so our bodies are alert, energized and ready for work and play. This is a problem as 76% of Americans look at their digital devices in the hour before attempting to go to sleep. [2, 8]
Brian Chou, OD, FAAO, FSLS, is in private practice in San Diego at ReVision Optometry.
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