Luminous Output

See also: Output

The luminous output of a source of light is the Rapport between the luminous Flow emitted by this source of light and the power absorptive by the source. It is thus expressed in lumen S by Watt (lm/W).

If one notes P \, the power received by the source, generally in electric form, and F \, emitted luminous flow, then the luminous output \ eta \, is worth by definition: \ eta = \ frac {F} {P}

Contributions to the luminous output

One can distinguish two contributions in this term:

  • the first contribution is the energetic efficiency of the source, noted \ rho \, , which expresses that all the received power is not converted into radiation, but that a part is lost in heating (conduction and Convection). That is to say \ Phi \, the radiant Energy flux emitted, then:

\ rho = \ frac {\ Phi} {P}
It is a Grandeur without dimension because it is the ratio of two powers.

  • the second contribution is the Apparent brightness V \, du radiation. It translates the fact that a part only of the radiation is perceived in the form of luminous flow, the remainder being a new loss of heat in the form of radiation invisible for the eye. V = \ frac {F} {\ Phi}
    Lorsque the source is not monochromatic but that its wavelength belongs to an extended field, the radiant energy flux is worth: \ Phi = \ int \ Phi_ \ lambda D \ lambda, where \ Phi_ \ lambda \, is the radiant energy flux emitted with the wavelength \ lambda \, .
    Le luminous flow is worth him: F = \ int \ frac {V_ \ lambda} {L} \ Phi_ \ lambda D \ lambda, where V_ \ lambda \, is a function without dimension called spectral Apparent brightness, expressing the sensitivity of the eye to the various wavelengths, and L \, is a numerical value of which the reverse 1/L \, is worth 680 lm/W.
    L' apparent brightness is thus calculated by: V = \ frac {\ int V_ \ lambda \ Phi_ \ lambda D \ lambda} {L \ int \ Phi_ \ lambda D \ lambda} . It with the size of 1/L.

All in all, the luminous output is the product of these two contributions: \ eta = \ rho \ cdot V

Examples of values for various types of Lamp S, classified by increasing output

  • With incandescence 10 to 15 Halogenous lm/W

  • 15 to 25 lm/W
  • Electroluminescent diode 15 with more than 100 lm/W
  • Mercury high pressure 35 to 60 lm/W
  • Lamp fluocompacte 50 to 90 lm/W
  • fluorescent Lamp 60 to 95 lm/W
  • metal Halides 65 to 120 lm/W
  • Sodium high pressure 80 to 150 lm/W
  • Sodium low pressure 100 to 200 lm/W

Examples

The table below indicates the apparent brightness and the luminous output of various sources of light:

Notice

Often, this value of the luminous output is called itself apparent brightness , in particular by the majority of the manufacturers of lamps. That can lend to confusion because, rigorously, the apparent brightness is with the energetic efficiency only one of the two factors of the luminous output total.

References

See too

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