100 mm

Introduction
The most important light variables in signaling technology are:
• light intensity
• luminous fl ux
• illumination intensity
Light intensity is measured in Candela [cd].
The light intensity is the radiation power of a light source per dihedral angle, weighted with the spectral sensitivity
of the eye. The directional dependence of the luminous fl ux is represented. This is particularly important in signal
technology, since it is not about illuminating a room, but rather about the directed transmission of light to the
observer.
light intensity [cd] = luminous flux [lm] / dihedral angle [sr]
For example, the light intensity of a household candle is around 1 cd.
Luminous fluxΦ is expressed in Lumen [lm].
The luminous fl ux is a measure of the entire visible radiation that is radiated in all directions from a source of light
and, as opposed to light intensity, is not directionally dependent.
Illumination intensity is expressed in Lux [lx].
The illumination intensity describes the amount of the luminous fl ux that strikes a given area. It is the quotient of
luminous fl ux and area.
illumination intensity [lx] = luminous flux [lm] / area A (m 2 )
The illumination intensity is inversely proportional to the square of the distance. A doubling of the distance therefore
results in the illumination intensity being reduced to one quarter.
Light intensity
Luminous fl ux
Light density
Illumination intensity
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