Main source of light on Earth is from the Sun. Exposure to the ultraviolet radiation (UVR) in sunlight has both beneficial and deleterious effects on human health.
The best-known benefit of sunlight is its ability to boost the body’s vitamin D supply; most cases of vitamin D deficiency are due to lack of outdoor sun exposure.
Artificial light is composed of visible light as well as some ultraviolet (UV) and infrared (IR) radiations, and there is a concern that the emission levels of some lamps could be harmful for the skin and the eyes.
The majority of lamps used for normal lighting conditions are RG0 (lowest risk) and most of the rare exceptions are RG1 (minimal risk: not hazardous during normal circumstances). Provided that these lamps are used at the distances for which they were intended, the UV, IR or blue light radiation they emit should pose little or no risk to non-photosensitive people.
Recent measurements show that a large proportion of the UV radiation from tungsten halogen lamps is in the UVC range, which is particularly harmful.
UVA radiation (95–97% of the UVR that reaches Earth’s surface) penetrates deeply into the skin, where it can contribute to skin cancer indirectly via generation of DNA-damaging molecules such as hydroxyl and oxygen radicals. Sunburn is caused by too much UVB radiation; this form also leads to direct DNA damage and promotes various skin cancers. Both forms can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers. Excessive sun exposure can also cause cataracts and diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses.
After issues of safety, light pollution has a wide range of negative effects on human health such as disrupting circadian rhythms, melatonin levels, and contributing to sleeping disorder.