Light aids us in seeing, but the latest research development has shown that light is required not only for vision but is also very important for biological function. This field of science is known as non-visual pathway. Our research has been investigating two different wavelengths of light: one is blue and the other is violet. Blue light determines the circadian rhythm, mood, and memory through the melanopsin (OPN4) photoreceptor. Violet light controls the circadian rhythm of the eye and partially, the body. A significant recent study has demonstrated that violet light controls the size of the eyeball. We have termed this “violet light hypothesis for myopia control.” In this talk I will cover the general concepts of light for health and discuss the specific effects of blue and violet lights on human health.