Re: [TRNSYS-users] Radiation in lux

[David Bradley <bradley@tess-inc.com>]

Werner,
  lux (or lumens/m2) is a measure of luminous power as opposed to a measure of "pure" radiative power. A measure of pure radiative power weights all wavelengths of the radiation equally whereas measures of luminous power account for the fact that the eye is more sensitive to visible light wavelengths. There is certainly a relationship between the amount of solar radiation amount and the luminous radiation called the luminous efficacy. I have seen methods for calculating the luminous efficacy of certain window and skylight configurations but there is also a luminous efficacy associated with the atmosphere. If you run one of the TMY2 sites from the US, and look at the output for illuminance and solar radiation, you can divide one by the other and see what the general magnitude of the luminous efficacy is.
That was probably more informative than helpful...
Cheers,
 David


keilholz, werner wrote:

Dear TRNSYS users,

 

I just ran into a weather data file with solar radiation data in ‘lux’.

 

Now, that’s even worse than the usual kj/hr.m^2… Illuminance (in lux or cd/m^2) is a different dimension than Flux (in W/m^2), but one might think there should be some relation between the two.

Is there a way to compute (diffuse?) radiation from it?

 

Thanks,

Werner Keilholz
TIDS / IIL / Ingénieur

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