# Irradiance values under multiple LIGHT sources

Dear all,

I am currently trying to obtain the irradiance value on a horizontal surface (0 0 0 0 0 1) under 10 direct light sources (-ab 0). Light sources are created by mapping 10 LIGHT materials on 10 SOURCE surfaces. Each SOURCE subtends an angle of 0.5 deg, and they are at least 3.75 deg apart.

When the 10 light sources are applied simultaneously in the simulation, it gives an irradiance value of approx. 0.5% less than the mathematically-derived value. When the light sources are simulated separately and then the 10 irradiance values are added together, the value is (almost) identical to the derived value.

Could anyone advise how the discrepancy occurs and how it can be avoided? Thanks a lot.

Kam

···

The discrepancy is likely caused by the adaptive source sampling. Set -dt 0 to switch this off.

-Greg

···

From: Kam Shing Leung <[email protected]>
Date: December 9, 2008 12:13:31 PM PST

Dear all,

I am currently trying to obtain the irradiance value on a horizontal surface (0 0 0 0 0 1) under 10 direct light sources (-ab 0). Light sources are created by mapping 10 LIGHT materials on 10 SOURCE surfaces. Each SOURCE subtends an angle of 0.5 deg, and they are at least 3.75 deg apart.

When the 10 light sources are applied simultaneously in the simulation, it gives an irradiance value of approx. 0.5% less than the mathematically-derived value. When the light sources are simulated separately and then the 10 irradiance values are added together, the value is (almost) identical to the derived value.

Could anyone advise how the discrepancy occurs and how it can be avoided? Thanks a lot.

Kam