In this decade, the research on non-visual effects of light on circadian system progressed dramatically thanks to the discovery of the novel photoreceptor and the action spectrum. Based on the action spectrum on depolarization of melanopsin-expressing ganglion cells and on melatonin suppression, some calculation methods to estimate the impact of non-visual effects of light have been proposed recently. DIN (German institute for standardization) has established the pre-standard which enables to calculate relative effectiveness of various light sources. Lighting Research Center in the US has proposed a unique calculation method which enables to estimate melatonin suppression rate. There still are many research challenges to tackle with including investigation on the difference of action mechanism in monochromatic and polychromatic light exposure.
