MIT OCW Biology
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Both ultraviolet and infrared energy are invisible to the human eye. Infrared (IR) is heat energy, so it can damage the skin (burn). IR has a longer wavelength, however, so it won't penetrate the skin deeply UV energy, because of its shorter wavelength, has the capability of penetrating more deeply into the skin, and in doing so damaging deeper layers of skin cells. In addition, UV light is dangerous because it can mutate DNA. Source: (Googled it)
There are three types of UV radiation, categorised by wavelength: UVA, UVB and UVC. UVA can cause sunburn, DNA (cell) damage in the skin and skin cancer. UVB causes skin damage and skin cancer. Ozone stops most UVB from reaching the earth's surface. UVC is the most dangerous type of UV. Ozone in the atmosphere absorbs all UVC so none reaches the earth's surface.
The sun sends out different types of radiation – visible light that we see as sunlight, infrared radiation felt as heat and UV radiation that we can't see or feel. Levels of ultraviolet (UV) radiation from the sun change throughout the day, every day, each month, each season, each year,
Both infrared and ultraviolet energy are Electromagnetic invisible to the human eye . Infrared - Infrared radiation is popularly known as "heat radiation", but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for only 49% of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths.light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometres (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz, Most of the thermal radiation emitted by objects near room temperature is infrared. Also Thermal-infrared imaging is used extensively for military and civilian purposes. Military applications include target acquisition, surveillance, night vision, homing and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm (micrometers). Non-military uses include thermal efficiency analysis, environmental monitoring, industrial facility inspections, remote temperature sensing, short-ranged wireless communication, spectroscopy, and weather forecasting. Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, that is, in the range between 400 nm and 10 nm, corresponding to photon energies from 3 eV to 124 eV. It is so-named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. These frequencies are invisible to humans, but near UV is visible to a number of insects and birds.UV light is found in sunlight (where it constitutes about 10% of the energy in vacuum) and is emitted by electric arcs and specialized lights such as mercury lamps and black lights. It can cause chemical reactions, and causes many substances to glow or fluoresce, most people are aware of the effects of UV on the skin, called suntan and sunburn. In addition to short-wavelength UV blocked by oxygen, a great deal (>97%) of mid-range ultraviolet (almost all UV above 280 nm and most up to 315 nm) is blocked by the ozone layer, and like ionizing short-wavelength UV, would cause much damage to living organisms if it penetrated the atmosphere. Indeed, the existence of the ozone layer is what allows life to exist on land, outside of the deep oceans. After atmospheric filtering, only about 3% of the total energy of sunlight at the zenith is ultraviolet, and this fraction decreases at other sun angles. Much of it is near-ultraviolet that does not cause sunburn, but is still capable of causing long-term skin damage and cancer. An even smaller fraction of ultraviolet that reaches the ground is responsible for sunburn and also the formation of vitamin D (peak production occurring between 295 and 297 nm) in all organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human health.