Blue light (between 440 and 495 nanometers) is the one that gets in the way of melatonin production – the hormone that helps you sleep. Even a small amount of blue light at night can fool your body into thinking it’s still daytime. That makes it harder to feel sleepy. But violet light (around 420 nanometers) doesn’t get in the way of melatonin as much, especially if your eyes have already been in light for about 30 minutes.