Glossary of Solar Radiation Resource Terms

Other relevant glossaries


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IEA - the International Energy Agency, an autonomous agency linked to the Organisation for Economic Co-operation and Development.


IEEE - the Institute of Electrical and Electronics Engineers, Inc.


Illuminance - solar radiation in the visible region of the solar spectrum to which the human eye responds.


Incident Angle - the angle that a ray (of solar energy, for example) makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°. The figure accompanying the description of airmass illustrates a solar angle of incidence of 48.2° to a horizontal surface.


Incident Radiation - incoming radiation; i. e., radiation that strikes a surface.


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). Infrared radiation is associated with heat energy.


Insolation - solar radiation on the surface of the Earth. This term has been generally replaced by solar irradiance because of the confusion of the word with insulation.


Inversion - typically, a temperature inversion, or a zone in the atmosphere in which the temperature increases with altitude, instead of the expected decrease. In general, an inversion is any reversal of the normal trend of the property of an atmospheric substance with respect to altitude.


Interferometer - an instrument for determining the spectral distribution of irradiance. A light interferometer divides a beam of light into two or more beams and brings the beams back together. The recombined beams shine on a screen or another object like a detector surface. The resulting interference fringes can be used to determine the spectral nature of light.


Irradiance - the rate at which radiant energy arrives at a specific area of surface during a specific time interval. This is known as radiant flux density. A typical unit is W/m2.


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