Different colors of light affect the body's internal clock differently; blue light at a specific wavelength strongly activates circadian pathways, while red light at another wavelength has minimal...

One hour of red LED light at night temporarily lowers melatonin levels similarly to blue light, but melatonin rebounds after two to three hours, suggesting red light may interfere less with the body's natural sleep-wake cycle over time.

Exposure to blue light from LEDs for three hours reduces melatonin levels more than red light in young adults, with melatonin staying low under blue light but recovering under red light.

In healthy adults who have had limited sleep for two nights, exposure to blue light in the morning may shift the timing of melatonin release to occur earlier than when exposed to dawn-like or dim light.