Electromagnetic radiation (or "extreme") ultraviolet. UV, with X-ray and gamma radiation, are referred to as ionizing radiation due to the ability of photons of this radiation to produce ions and free radicals in materials (including living tissue). Since such radiation can severely damage life at energy levels that produce little heating, it is considered far more dangerous (in terms of damage-produced per unit of energy, or power) than the rest of the electromagnetic spectrum. The heat ray is an application of EMR that makes use of microwave frequencies to create an unpleasant heating effect in the upper layer of the skin. A
Optical radiation of the spectrum, from UV to IR, can produce thermal injury to the surface layers of the skin, including the eye. When it comes from natural sources, this sort of thermal injury might be called a sunburn. However, thermal injury from infrared radiation could also occur in a workplace, such as a foundry, where such radiation is generated by industrial processes. At the other end of this range, UV light has enough photon energy that it can cause direct effects to protein structure in tissues, and is well established as carcinogenic in humans. Occupational exposures to UV light occur in