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 450 nm in the visible spectrum. Despite a lack of concurring scientific evidence, HEV light has sometimes been claimed to be a cause of age-related macular degeneration. Some sunglasses and beauty creams specifically block HEV, for added marketing value.
Blue-light hazard is the potential for photochemically-induced retinal injury resulting from electromagnetic radiation-exposure at wavelengths primarily between 400 and 450 nm. Researchers have not studied the phenomenon in humans, but only ( and inconclusively) in some rodent, primate, and in vitro studies. Photochemically-induced retinal injury is 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 in a susceptible strain of mice to cause a problem in the process so that 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 approximately 450 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 in household light-bulbs.
An unpublished and non peer-reviewed 2013 in vitro study, financed by skin-care company Lipo Chemicals, used shorter blue-band spectrum LED lights and claimed that prolonged exposure may permanently damage the pigment epithelial cells of the retina. However, 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, which is not deemed to be a realistic light exposure..
One study has given more insight into the blue-light hazard: permanent damage to the eye cells, as reported by a research-team from Toledo University especially for children, who are big users of LED screens (smartphones, tablets...).
Blue light within the range 400-450 nm has been reported in a number of studies to be effective as local treatment of eczema and psoriasis, as it purportedly helps dampen the immune response. Recent studies have also shown improvement of facial acne upon exposure to a LED emitting at 414 nm. A combination of exposure to red and blue lights is used more and more in clinical dermatologic therapies. Constructors such as Philips currently develop devices and techniques emitting in the blue visible spectrum to be used in dermatologic therapy.
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Un team dell'Università di Toledo, infatti, afferma dalle pagine di Scientific Reports di aver scoperto il meccanismo che conduce alla morte dei fotorecettori della retina che ci consentono di vedere: la luce blu trasformerebbe una molecola chiamata retinale, indispensabile per la vista, in un killer cellulare. [...] 'E i fotorecettori non si rigenerano nell'occhio', fa notare Kasun Ratnayake, uno degli autori della ricerca. 'Una volta morti, non ce ne saranno di nuovi a sostituirli'.
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