Your eyes have special cells called ipRGCs that help set your body clock. These cells don’t help you see – they help your brain know what time it is. They’re most sensitive to blue light between 440–495 nanometers and use something called melanopsin to send signals to your cells (each cell has it’s own circadian rhythm). When the light is bright (blue light), they work with your regular eye cells to keep your body in sync with the day – causing you to feel alert.