The UVB radiometer measures global solar ultraviolet irradiance between 280 and 320 nm, peaking in response at about 300 nm. This covers the part of the solar spectrum that is responsible for sunburns on human skin. The protective dome over the receiving surface is made of a special glass that transmits visible and UV wavelengths. A feature that differentiates this instrument from the solar pyranometer is that the receiving surface beneath the dome is not the detector. Rather, it is a UV-transmitting black filter that screens out visible wavelengths, except for a small bit of red light. Beneath this filter, the transmitted energy cascades through a layer of UVB-sensitive phosphor, where it is absorbed and re- emitted as visible light (primarily green). The visible light then passes through a green filter, below which its intensity is measured by a photodiode detector. The UVB pyranometer is thermally stabilized at 45 degrees Celcius to maintain all components at a nearly constant operating temperature, and to keep the body of the instrument free of moisture, snow, and frost.