Research of angular uniformity of colorimetric parameters of led lamps and led luminaires

Abstract

The results of research of the angular uniformity of color parameters of LED lamps and luminaries for ambient light are presented. It is shown that the use of completely diffusing diffusers provides angular uniformity within three step Mac-Adam ellipses. Lamps both with or without diffusers that enable directional light scattering can have a rather large angular unevenness. Based on the study of commercial samples, it was found that the angular color unevenness Δu’, v’ for LED lamps and luminaries with diffusely transmitting diffusers does not exceed 0.0031 at the uniform–chromaticity–scale diagram CIE (u’, v’) (located within 3 step MacAdam ellipses). Lamps with prismatic diffusers and transparent protective plastic have an angular unevenness of almost 0.01 (out of 7 step MacAdam ellipses). The use of diffuse light diffusers, in addition to increasing the uniformity of color, reduces the correlated color temperature (CCT). For CCTs exceeding 6000 K, the decrease can reach 1000 K or more. At low CCTs changes are not so significant – no more than 200 K. When changing the viewing angle, the overall color rendering index Ra for lamps and luminaries with completely diffusing diffusers practically does not change. For lamps without light diffusers, as well as for lamps with prismatic diffusers and lens optics, the difference may reach 7 units or more of the standard deviation of the comparison color. In order to inform consumers about the unevenness of color parameters at different viewing angles, it is proposed to indicate the angular uniformity in addition to average color values in the catalogues. This shall only apply to LED lamps and luminaries used for indoor lighting and those that have angular unevenness that exceed the 3 step MacAdam ellipses.