IEVref:845-31-025ID:
Language:enStatus: Standard
Term: Allard's law
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Definition: law relating the illuminance, Ev, produced on a surface (which is normal to the direction of the light source and sufficiently distant for the light source to be considered as a point source) by a light source to the luminous intensity, Iv, of the light source in the direction of the surface, to the distance, d, between the surface and the light source, and to the atmospheric transmissivity, T, which is assumed to be uniform

E v = I v d 2 T d/ d 0 MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgaruWqVvNCPvMCG4uz 3bqee0evGueE0jxyaibaieYdi9WrpeeC0lXdh9vqqj=hEeeu0lXdbb a9GqFj0xb9Lqpepeea0xd9q8qiYRWxGi6xij=hbba9q8aq0=yq=He9 q8qiLsFr0=vr0=vr0db8meaabaGacmGadiWaaiWabaabaiaafaaake aacaWGfbWaaSbaaSqaaiaabAhaaeqaaOGaeyypa0ZaaSaaaeaacaWG jbWaaSbaaSqaaiaabAhaaeqaaaGcbaGaamizamaaCaaaleqabaGaaG OmaaaaaaGccaWGubWaaWbaaSqabeaacaWGKbGaai4laiaadsgadaWg aaadbaGaaGimaaqabaaaaaaa@450F@

where d0 is the length specified in the definition of T

Note 1 to entry: The formula in the definition is sometimes written:

E v = I v d 2 T δ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgaruWqVvNCPvMCG4uz 3bqee0evGueE0jxyaibaieYdi9WrpeeC0lXdh9vqqj=hEeeu0lXdbb a9GqFj0xb9Lqpepeea0xd9q8qiYRWxGi6xij=hbba9q8aq0=yq=He9 q8qiLsFr0=vr0=vr0db8meaabaGacmGadiWaaiWabaabaiaafaaake aacaWGfbWaaSbaaSqaaiaabAhaaeqaaOGaeyypa0ZaaSaaaeaacaWG jbWaaSbaaSqaaiaabAhaaeqaaaGcbaGaamizamaaCaaaleqabaGaaG OmaaaaaaGccaWGubWaaWbaaSqabeaacqaH0oazaaaaaa@4347@

where the exponent, δ, in Tδ is the numerical value of the distance, d, measured with d0 as "unit".

Note 2 to entry: Taking into account the relationship between atmospheric transmissivity, T, and meteorological optical range, v, given in Note 2 to entry of the definition of "meteorological optical range", Allard's law can also be written as:

E v = I v d 2 ( 0,05 d/v ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgaruWqVvNCPvMCG4uz 3bqee0evGueE0jxyaibaieYdi9WrpeeC0lXdh9vqqj=hEeeu0lXdbb a9GqFj0xb9Lqpepeea0xd9q8qiYRWxGi6xij=hbba9q8aq0=yq=He9 q8qiLsFr0=vr0=vr0db8meaabaGacmGadiWaaiWabaabaiaafaaake aacaWGfbWaaSbaaSqaaiaabAhaaeqaaOGaeyypa0ZaaSaaaeaacaWG jbWaaSbaaSqaaiaabAhaaeqaaaGcbaGaamizamaaCaaaleqabaGaaG OmaaaaaaGccaaMe8UaaiikaKaaajaaicdacaGGSaGaaGimaiaaiwda kmaaCaaaleqabaGaamizaiaac+cacaWG2baaaOGaaiykaaaa@4986@ .

Note 3 to entry: This entry was numbered 845-11-27 in IEC 60050-845:1987.


Publication date:2020-12
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