Ionizing radiation from medical imaging. Average man-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine. Natural background radiation comes from five primary sources: cosmic radiation, solar radiation, external terrestrial sources, radiation in the human body, and radon. The background rate for natural radiation varies considerably with location, being as low as 1.5 mSv/a (1.5 mSv per year) in some areas and over 100 mSv/a in others. The highest level of purely natural radiation recorded on the Earth's surface is 90 µGy/h (0.8 Gy/a) on a Brazilian black beach composed of monazite. The highest background radiation
Non-ionizing radiation UV band, including much of the band that is formally non-ionizing. Ultraviolet light induces melanin production from melanocyte cells to cause sun tanning of skin. Vitamin D is produced on the skin by a radical reaction initiated by UV radiation. Plastic (polycarbonate) sunglasses generally absorb UV radiation. UV overexposure to the eyes causes snow blindness, common to areas with reflective surfaces, such as snow or water. Light, or visible light, is the very narrow range of electromagnetic radiation that is visible to the human eye (about 400–700 nm), or up to 380–750 nm. More broadly, physicists refer to light as