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Schierz, C. IS LIGHT WITH LACK OF RED SPECTRAL COMPONENTS A RISK FACTOR FOR AGE-RELATED... 4 Proposal for an “AMD protection index” In order to compare the potential of different light sources with regard to positive or negative effects on AMD a tentative “AMD protection index” is proposed. It is intended that this index represents the “oxidant – antioxidant balance” within the RPE-cells. The “weights” which can be placed on each side of the “beam-balance” are the photobiological quantities 𝐵 and 𝑅 calculated as spectrally weighted radiances: 𝐵 𝑆𝜆 ∙ 𝑏𝜆 ∙ d𝜆 (1) 𝑅 where 𝐵 𝑅 𝑆𝜆 𝑏𝜆 𝑟̅ 𝜆 𝑆 𝜆 ∙ 𝑟̅ 𝜆 ∙ d𝜆 (2) is the photobiological quantity (balance weight) for negative effects; is the photobiological quantity (balance weight) for positive effects; is the spectral distribution of the light source radiation; is the action spectrum for negative effects; is the action spectrum for positive effects. The construction of an AMD protection index follows the principle of Michelson contrasts (hence the selection of the letter C): 𝐶 𝑅 𝑓 ∙ 𝐵 (3) 𝑅 𝑓 ∙ 𝐵 where C is the proposed AMD protection index with values between -1 and +1; 𝑓 is a factor for zero adjustment. The more positive the AMD protection index is, the better the light protects against AMD; the more negative the index is, the riskier is the light for AMD. However, since at present it is not possible to know where the equilibrium between blue and red spectral components could be, a zero adjustment factor 𝑓 has been introduced. Until the knowledge of the best choice of the action spectra and of the equilibrium with a reasonable value for 𝑓 is available, the AMD protection index should only be used for relative comparisons. For the calculations presented in Section 5, the action spectra 1 and 5 of Figure 3 have been chosen and 𝑓 was selected to give the daylight illuminant D45 an AMD protection index of zero. The reasoning behind this is the result from epidemiology that sunlight may present a risk for AMD (Cruickshanks et al., 2001) and therefore daylight with Tcp > 4500 K should get negative index values. 5 Influence of CCT, CRI and peak wavelength on the AMD protection index. For orientation, initial calculations of the relative impact on AMD for different light source spectra (LEDs, fluorescent lamps, Planckian radiator and daylight) are performed by means of the AMD protection index given in Equation (3). Although, generally, lower correlated colour temperature Tcp (CCT) is associated with higher a AMD protection index (Figure 4), there are considerable differences between different types of light sources. For example at 3000 K, due to the lack of red spectral components, LEDs or fluorescent lamps have a lower AMD protection index than a Planckian radiator (e.g. halogen incandescent lamp) with the same colour temperature. This also applies for LEDs imitating the sun spectrum (e.g. SunLike, Seoul Semiconductor; see Figure 4). Figure 5 shows the impact of specific LED properties for a fixed CCT of 4000 K: The higher the CIE 1974 general colour rendering index Ra (CRI) and the LED peak wavelength are, the better the AMD protection index will be. The lack of red spectral components is even more elucidated with the special colour rendering index R9, which describes the light source accuracy for colour fidelity of red objects. The R9 correlates better with the AMD protection index than the CRI (compare left and right in Figure 5). 118 Proceedings of 29th CIE Session 2019PDF Image | LIGHT WITH LACK OF RED SPECTRAL COMPONENTS v amd
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