IEVref:845-21-111ID:
Language:enStatus: Standard
Term: useful luminous flux, <of a directional light source>
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Symbol: Φv,u,α
Φu,α
Definition: part of the luminous flux of a light source that contributes predominantly to the lighting task

Note 1 to entry: For non-directional light sources, the useful luminous flux is the total luminous flux of the light source.

Note 2 to entry: For directional light sources the useful luminous flux is the partial luminous flux in a defined cone angle, the axis of the cone being the optical beam axis of the light source.

Note 3 to entry: The cone angle, α, which can be expressed either in degree (°) or radian (rad), is given by the full conic angle and has to be specified, e.g. Φu,90° or Φu,π/2.

Note 4 to entry: The optical beam axis of a light source is the axis about which the luminous intensity is substantially symmetrical.

Note 5 to entry: The useful luminous flux is expressed in lumen (lm).


Publication date:2020-12
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