Abstract
The high blue proportion of phosphor-conversion white-light emitting diodes (pc-LEDs), especially of those with higher correlated color temperatures (CCT), raises concern about photochemically induced retinal damages. Although almost all general lighting service LEDs are safe, other applications exist, like spotlights for theatres or at construction sites, that can pose a severe blue-light hazard (BLH) risk, and their photobiological safety must be assessed. Because of required but challenging radiance measurements, a calculative approach can be supportive for risk assessment. It is the aim of this work to exploit Gaussian functions to study LED parameter variations affecting BLH exposure. Gaussian curve approximations for color LEDs, the BLH action spectrum, and the spectral luminous efficiency for photopic vision enabled analytically solving the BLH efficiency, , and the BLH efficacy of luminous radiation, . It was found that sigmoidal functions describe the CCT dependence of and for different color LEDs with equal spectral bandwidth. Regarding pc-LEDs, variations of peak wavelengths, intensities, and bandwidths led to linear or parabolic shaped chromaticity coordinate correlations. and showed pronounced CCT dependent extrema that might be exploited to reduce BLH. Finally, an experimental test of the presented Gaussian approach yielded its successful applicability for color and pc-LEDs but a minor accuracy for blue and green LEDs.
Highlights
Semiconductor based light-emitting diodes (LEDs) have an exceptionally successful history, for example, with the blue LED Nobel prize [1], and their importance is still growing for general lighting service (GLS) lamps and for a wide range of modern technologies
The blue-light hazard (BLH) weighted and the luminous signal, SB and Sv, Equations (3) and (4), respectively, can be solved analytically for color LEDs because S(λ) as well as both weighting functions being parametrized by exponential functions with a quadratic term as exponent
Analyzing the peak wavelength dependence showed that photochemically induced retinal damage is highest for a blue LED with λ0 = 444.8 nm, and that a green LED with λ0 = 559.1 nm is perceived as the brightest one
Summary
Semiconductor based light-emitting diodes (LEDs) have an exceptionally successful history, for example, with the blue LED Nobel prize [1], and their importance is still growing for general lighting service (GLS) lamps and for a wide range of modern technologies. One of the most important milestones, was the development of blue-LED chips and thereby white-light emitting diodes. White light can be generated technically either by superimposing at least two complementary wavelengths with associated power ratios [2] or by an additive mixture ( in multi-channel systems) of the three primary colors red, green, and blue (sometimes with amber). Most common are phosphor-conversion white-light emitting diodes (pc-LEDs) [3] equipped with a blue-LED chip, typically made of indium gallium nitride (InGaN), which excites an yttrium aluminum garnet (YAG) phosphor to yellow fluorescence [4]. The high luminous efficiency and the long life up to thousands of hours in conjunction with low
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