High-energy visible light
In ophthalmology, high-energy visible light (HEV light) is high-frequency, high-energy light in the violet/blue band from 400 to 500 nm in the visible spectrum. HEV light has been suggested as a cause of age-related macular degeneration. Some sunglasses are now designed specifically to block HEV.
Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from electromagnetic radiation exposure at wavelengths primarily between 400 and 500 nm. This study has not been done in humans, only inconclusively in some rodent, primate, and in vitro studies. The mechanisms for photochemical induced retinal injury are caused by the absorption of light by photoreceptors in the eye. Under normal conditions when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.
Absorption of blue light, however, has been shown in rats and a susceptible strain of mice to cause a reversal of the process where cells become unbleached and responsive again to light before they are ready. At wavelengths of blue light below 430 nm this greatly increases the potential for oxidative damage. For blue-light circadian therapy, harm is minimized by employing blue light at the near-green end of the blue spectrum. "1-2 min of 408 nm and 25 minutes of 430 nm are sufficient to cause irreversible death of photoreceptors and lesions of the retinal pigment epithelium. ... The action spectrum of light-sensitive retinal ganglion cells was found to peak at 470-480 nm, a range with lower damage potential, yet not completely outside the damaging range." A 2014 study found that LEDs cause retinal damage even in settings where they are used indirectly, such as household light bulbs.
A 2013 in vitro study using shorter blue band spectrum LED lights indicated that prolonged exposure may permanently damage the pigment epithelial cells of the retina. According to a specialist, the test conditions were the equivalent of staring at a blue light equivalent to a 100 watt incandescent source from 20 cm (8 in) for 12 hours.
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