| The ACGIH (American Conference of Governmental and Industrial Hygienists) has specified maximum exposure limits to energy in this part of the spectrum, known as die bluelight hazard limit. More recently, the IESNA has published an algorithm for calculating the blue-light hazard based on the ACGIH recommendations and a framework for classifying and labeling light sources according to their potential for risk
The optical media of the eye (Figure 1) transmit most visible and near-IR (out to about 1400 nm) energy to the retina and absorb most, but not all, near-UV radiation. IR energy tends to elevate the temperature of the optical media and may increase risk of IR or "glassblower's" cataract.8 UV energy can cause photokeratitis, a painful inflammation of the outer corneal layer, and may also be a contributing factor in many forms of cataract.1 Because the energy reaching the retina falls largely between 400 and 1400 nm, this region of the spectrum is termed the retinal hazard region
Animal studies have shown, however, prolonged exposure to luminances near those of present T8 and compact fluorescent lamps might permanently affect vision in some species,9 although such effects have never been documented in humans, and these luminances are not considered hazardous to humans.4
These results led researchers to the conclusion light can contribute to harmful chemical reactions in the retinal media, and the resulting lesions are termed photochemical lesions. Such lesions are areas of discoloration without distinct borders on the retina visible to the ophthalmologist, and are the primary symptom of photochemical damage. The precise nature of these chemical reactions are not currently understood.4
In some animals, it was found the action spectrum for photochemical lesions was similar to the absorption spectrum of melanin.11,18 On the other hand, exposure to human pigment epithelium cells resulted in photochemical lesions appearing to be related not to melanin, but rather, another chemical.
The procedure specified by the IESNA for calculating the blue-light hazard is published in recommended practice document ANSI-/IESNA RP-27.4 It provides algorithms for both extended-area and near-point sources, and is not discussed in detail in this report. The algorithms allow the determination of the maximum time and intensity within an eight-hour period recommended to protect against photochemical damage to the retina. The calculated limits incorporate large safety margins to ensure against retinal damage and even the maximum permitted exposures should not result in photochemical damage.10
For practical purposes with "white" light sources, any condition resulting in direct exposure to luminances under 10,000 cd/m2 is unlikely to present a risk of photochemical injury to the retina.4 For such sources, calculation of the blue-light hazard is not necessary.
However, because fluorescent lamps also have low luminances (T12 lamps: 8000 cd/m2; T8 lamps: 11,000 cd/m2; T5 lamps: 20,000 cd/m2), their potential for risk of photochemical injury is negligible, as demonstrated by Table 1.
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