I want to use IES profile with an area light. My understanding is that the IES file assume the source to be a point light. That is in case of (large)area light the measurements are taken at a distance(normally 5 times the major dimension of the light source) that even an area light can be considered as a point light. However I am confused on how a measurement taken at say 12m can be used to calculate the contribution of the luminaire at shorter distances?

Also as the IES file has intensities values rather than the radiance,

  1. Is the below formula correct for calculating the irradiance from the light source in the form of the integral over the area, when we have the intensities ?

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I am little bit uncertain on the solid angle formulation. Is this correct?

  1. well if the above is correct, I am not clear how this fits in a monte carlo ray tracer ? Are we sampling intensities here? What is the pdf? also currently in my ray tracer all light sources methods and properties needs radiance values of the light source instead of intensity how would this fit in?

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