Melatonin is a hormone that helps regulate and promote sleep, It's produced less of during daylight conditions -- however, any artificial lighting can dampen melatonin production (especially those high energy saving devices such as smart phone and computer screens and energy saving fluorescents, etcetera that produce 'blue light'). Blue light is part of the daylight spectrum and is detected by novel light sensitive cells in the eye (not rods or cones) that contain a photo pigment called "melanopsin" that is especially sensitive to blue light.
[This light detecting mechanism, intrinsically photosensitive Retinal Ganglion Cells (ipRGC) which regulates our inner sense of night and day, evolved before the ability to see.]
For those people who have a hard time falling asleep or suffer from sleeplessness in the middle of the night, this is relevant information.
Gadgets For Naturally Maximizing Melatonin: