Glossary of Solar Radiation Resource Terms

Other relevant glossaries


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Langley - Named for Samuel P. Langley (1834-1906), a pioneering solar energy researcher at the Smithsonian Institution, this unit of radiant flux is one calorie per square centimeter (cal/cm2).


Latitude - the angular distance from the equator to the pole. The equator is 0°, the North Pole is 90° North, and the South Pole is 90° South.


Light - usually the visual portion of the electromagnetic spectrum between infrared (about 8000 Angstroms or 800 nanometers(nm)) and ultraviolet (about 4,000 Angstroms or 400 nm); however, the term is sometimes used as a synonym for all electromagnetic radiation.


Line-focusing Concentrator - a system that tracks the path of the sun by pivoting on one axis (typically East-West or North-South), using shiny parabolic troughs to heat the collector fluid that passes through a tube at the focus. It derives its name from the fact that solar radiation is focused on a line instead of on a point. Below is an illustration from the Solar Radiation Data Manual for Flat Plate and Concentrating Collectors .


Local Apparent Time - The time of day based strictly on the longitude of the locality and not on "blocky" time zones. For example, when it is 12:00 Pacific Standard Time (USA) (assumed to be 120° West Longitude), it is 11:51 Local Apparent Time in Seattle, Washington (USA), at 122° 18' West Longitude.


Local Standard Time - The time of day based on the longitude of the zone meridian associated with a locality. In the USA, the zone meridians are known by the following names:

    LONGITUDE   NAME

    75° West     Eastern Standard Time

    90° West     Central Standard Time

    105° West    Mountain Standard Time

    120° West    Western Standard Time

    135° West    Alaska Standard Time

    150° West    Hawaii Standard Time


Longitude - the East-West angular distance of a locality from the Prime Meridian. The Prime Meridian is the location of the Greenwich Observatory in England and all points North and South of it.


Longwave Radiation - infrared radiation, radiation with wavelengths greater than those of the visible light (at about 8000 Angstroms or 800 nanometers(nm)) but shorter than those of microwaves (at about 1,000,000 Angstroms or 800,000 nm). Longwave radiation is associated with heat energy.


Lux - The International Standard (SI) unit of measure for luminous flux density at a surface. One Lux equals one lumen per square meter.


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