The solid angular luminous flux density in a given direction from a light source. It may be considered as the luminous flux on a small surface normal to the given direction, divided by the solid angle (in steradians) which the surface subtends at the source of light. Since the apex of a solid angle is a point, this concept applies exactly only to a point source. The size of the source, however, is often extremely small when compared with the distance from which it is observed, so in practice the luminous flux coming from such a source may be taken as coming from a point. See Candlepower, Photometry
McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The luminous flux emitted from a point per unit solid angle in a particular direction. The luminous intensity is the official base unit for light.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
a fundamental photometric quantity characterizing a source of visible radiation. It is in general different for different directions from the source. The luminous intensity is equal to the ratio of the luminous flux emitted by the source, in an infinitesimal (that is, very small) solid angle containing the given direction, to the solid angle. The unit of luminous intensity in the International System of Units is the candela. The concept of luminous intensity is applicable only at distances from the source that greatly exceed the source’s dimensions.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
luminous intensity[′lü·mə·nəs in′ten·səd·ē]
The luminous flux incident on a small surface which lies in a specified direction from a light source and is normal to this direction, divided by the solid angle (in steradians) which the surface subtends at the source of light. Also known as light intensity.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The luminous flux per unit solid angle in a specific direction from a point source of light; in practice, an interior source may be considered a point source if the distance exceeds 5 to 10 times the maximum source dimension of the luminaire
; in US Customary units, expressed in candlepower
; in SI units, expressed in candelas
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.