Light & Radiation Systems
Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined as global shortwave radiation, or shortwave irradiance, and is expressed
in Watts per square meter. Typical applications of pyranometers include incoming shortwave radiation measurement in agricultural, ecological, and hydrological
weather networks and solar panel arrays. Solar radiation is often used in evapotranspiration models.
Net radiation is the balance between incoming and outgoing shortwave and longwave radiation and is spatially and temporally variable due to changes in position of the sun with respect to Earth’s surface, changes in atmospheric conditions, and differences in land surface conditions. Net radiation is the main source of energy for the physical and chemical processes that occur in the surface-atmosphere interface, including photosynthesis and evapotranspiration. The Apogee SN-500 net radiometer is a four-component instrument, with individual upward- and downwardlooking pyranometers and pyrgeometers and on-board calculation of net shortwave, longwave and total net radiation. Typical applications of net radiometers include measurement of net radiation on surface flux towers and weather stations.
Ultraviolet (UV) radiation constitutes a portion of the electromagnetic spectrum from 100 to 400 nm, and classified by wavelength into three regions : UV-A (315 to 400 nm), UV-B (280 to 315 nm) and UV-C (100 to 280 nm). The erythema action spectrum provides an internationally accepted representation of the erythema-inducing effectiveness of wavelengths in the UV part of the spectrum, forming the basis of the UV index used for public health information.
Typical applications of UV sensors include the providing of real time public health information, total UV radiation measurement in outdoor environments or in laboratory use with artificial light sources (e.g., germicidal lamps).
Illuminance is a measurement of radiant energy on a surface, weighted by the human eye response, which is sensitive to radiation from about 380 to 780 nm but is most sensitive in the middle of this range near 555 nm. Sensors that measure illuminance are referred to by many names, including light sensors, photometric radiometers, photopic sensors, and lux sensors. Illuminance is quantified in units of lux or footcandles. Typical applications of illuminance sensors include determination of optimum light levels in indoor environments, public areas and sporting facilities.