I am having an issue with the light intentity for VRaylights. It is my wish to use the Vray physical camera in conjuction with Vray lights that are based on photometric units for my renders. To determe the proper exposure, film ISO, and f/stop for my physical camera, I use one of many online exposure calculators (like this one http://www.robert-barrett.com/photo/exposure\_calculator.html)
When I began to use Vray lights in my scene I began to notice that light intensity in the render were very high even to the physical intensity of the light that is specified is very low. I decided to do a little experiment. I wanted to see the difference between the intensity of a Vray light and an IES light. I know the lighting distribution will not be the same but the brightness of the room should be on the same order. My physical camera settings are as follows:
I set up the same scene using six ceiling mounted VRaylights each set to 825 lumens in lieu of the IES lights. Everything else including the camera exposure settings are the same. Here is the result
i am not sure at all, but as the vray light’s intensity is dependend on the size (= surface) of the light i guess you would have to model the glow-wire to make them match. But that might be complete bullshit.
Which VRay are you using? As far as I recall there was a bug in the Cameraparameters, The ISO settings were 100 times brighter than they should be and the V-Ray lights were twice darker than they should be, when the intensity was specified in lumens;
I am not sure which version this was and if this is correct in rc3 now. But I know that Vlado investigated the issue.
Before this thread dies and falls completely off the face of the earth, does anyone know if the problem that I have stated here is a bug/deficiency in VRay or is it something that I have done wrong? If it is a bug, will it be corrected in RC4 or in the final version of VRay 1.5? Usually someone like vlado would address this issue.
Yep, you should use the luminous power specified by the IES profile. In V-Ray 1.5 and later, a V-Ray light with a given luminous power will produce the same illumination as a photometric light with the same power.
Note, however, that the actual lumnious power described by the IES web data typically amounts to less power than the prescribed for the light (e.g. if the IES profile says it is for a 1700 lm light, the actual emitted power might be only 1300 lm; for the IES profiles that we examined here, this difference is typically about 65-75%).
Thanks vlado,
I was being stupid… underestimating the brightness of the sun. After doing some tests with my digi-cam, the ies light levels do seem correct in relation to the sun.
