Luminous Intensity

The luminous intensity of a light source is defined as the radiated power per solid angle, weighted by the spectral sensitivity of the eye. Or, with other words, as the luminous flux per solid angle. Adding up the light intensity in candelas over the entire solid angle in steradian (in maths: the integral of light intensity over the solid angle) delivers the light output in lumens. The light intensity can be increased if the radiation not evenly illuminates the surrounding space. For example: reflectors or lenses focus the emitted light of a light emitting diode on a certain region. In this region the light intensity increases whereas it decreases in the outlying regions.

Base unit is the candela (cd). It is a photometric unit and a measure for the strength of the light perception caused by the received radiation in the human eye.

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