# I can't get even similar irradiance values from a lamp.

How did you measure the UV reflectance of the surfaces of your box? Most paints drop off dramatically from the visible spectrum to UV. White paints may re-emit UV as visible so they appear "whiter" under daylight illumination. You really need to know the behavior of your paint with respect to ultraviolet wavelengths to do this correctly.

-Greg

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From: Minki Sung <[email protected]>
Date: March 14, 2009 10:52:03 PM PDT

I'm writing here for third time and I always sorry for just asking. I'm modeling a small box has a several bared cylindrical fluorescent lamps (actually UV lamps) inside and want to know the irradiance level on the surfaces of the box. The cylindrical lamps has 32mm in diameter and 540mm in length and The radiance of 44W/sr/m2 calculated with the UV output of the lamps (7.5W) was applied to the lamps. Before calculating the small box model I checked irradiance values with an experiment measuring UV intensity at the distance of 1 m and compared that with the same simple RADIANCE calculation and the result was reasonable. However, the calculation results are higher than those of experiments by 2~4 times with the small box model. The small box is not simple but not so complicated. I have modeled the lamp both as a cylinder and 72 polygons but there were not so much changes. Only one channel was used to calculate irradiances of UV from modeling to issuing results and only diffused reflections were assumed. Geometric errors or abnormal radiance distributions of lamps could be assumed to cause the discrepancy, but 2~5 times are too large
Here is my rtrace options.

cat pts_sensor.pts | rtrace -I -oov -ar 128 -ad 512 -as 256 -ab 2 -ds 0.02 uv.oct > uv.dat

It would be appreciated if anyone give me advice.

Sung

Hi!

irradiance level on the surfaces of the box. The cylindrical lamps
has 32mm in diameter and 540mm in length and The radiance of 44W/sr/
m2 calculated with the UV output of the lamps (7.5W) was applied to
the lamps.

Hm, how did you calculate the 44W/sr/m2 for the lamps? I get
7.5/(2*pi*0.54*0.032)=7.5/0.1086=69W/m2, divided by pi=21.99 W/m2sr.
This means that your light source is two times brighter than I would
expect it to be.

CU Lars.