Evaluation on the non-visual biological effects of light sources

Since the discovery of the third retinal photoreceptors and the spectral sensitivity curve of non-visual biological effects, people began to study on the non-visual biological effects of light sources. However, there is no a unified standard to evaluate it now. In order to solve this problem, we define two parameters, circadian efficacy K_C,v and circadian irradiance E_C, to analyse the effects quantitatively. We measured the relative spectral power distribution with a spectrometer for thermal radiation light sources, ceramic metal halide lamps, fluorescent lamps and LEDs. Then the circadian efficacy and irradiance of various light sources was calculated on the basis of the spectral sensitivity curve of non-visual biological effects C(λ). The results reveal that LEDs, fluorescent lamps and ceramic metal halide lamps with correlative colour temperatures (CCTs) from 2700 K to 6500 K, have similar circadian efficacy and irradiance, which is 0.45-0.54 W klm^-1 and 0.22-0.31 W m^-2 for CCT 2700 K, and 1.15-1.18 W klm^-1 and 0.58-0.59 W m^-2 for CCT 6500 K. And they are all smaller than that of the thermal radiation light sources. The circadian efficacy and irradiance of all light sources essentially increases with CCTs almost linearly.