Defining the luminous intensity
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The luminous intensity is a measure to describe the power of a light source to emit light in a given direction. The difference between luminous flux and the intensity is that the former is the total emitted light whereas the latter is the fraction that is emitted into a certain direction or into a certain solid angle.
Defining the luminous intensity
If a light source has no preferred direction and emits all its light evenly into all directions, it is said to be isotropic. In such a case, the luminous intensity in any direction multiplied by 4Pi (which is the full solid angle) is equal to the luminous flux.
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Some typical luminous
intensities
(GLS courtesy of Philips Lighting)