Lights in SR1

[pacha]

Hi all,

When I upgraded from the previous version to SR1 for SU; I noticed so many changes.
Regarding the Vray lights, now we have different units (Scalar, watts ...etc).
The main purpose of 3D modeling is to get a fair idea about the final look of the model when it will be done in reality.
Hence, lighting is one of the most important things here.
When I changed the multipliers of Vray lights (in my old models) to the new units (Watts), I did not get realistic results.
Instead of using a light whose intensity is 200 watts, I had to use 10000.

What's the problem ???

[dcauldwell_cg]

Re: Lights in SR1

Congratulations! I think you are the first person to raise the lighting 'units' question.

However, I am puzzled by your results, as my experience with vray rectangular lights is that if you use 'watts' then "A typical 100W light bulb only emits between 2 and 3 watts as visible light" so needs setting very low - like 1 or 2 watts.

I found it useful to read www.spot3d.com/vray/help/150SP1/light_params.htm

Sorry, but I don't know why you have found it necessary to set the level so high.

David

[dalomar_cg]

Re: Lights in SR1

You have officially opened up the Physical Lighting Units discussion, and its one thats quite complex. When it comes to lighting units it is very important to understand what the actual units themselves are describing. Depending on the units themselves there may be an absolute reference to intensity (which I believe Lumens and Watts are) or there may be other factors such as the area of the light that is being used.

Its also very important keep in mind that the exposure of the camera has a significant role in the final result of the light (as it always does). The real implementation of photometric lighting is based on varying the exposure of the camera to match those photometric intensities. IOW, if you just adjusted the intensity of the lights to what you needed and didn't think about you're camera exposure, you're no better off then using a non-physical unit.

I wish I could give you some more concrete definitions or something, but I am fuzzy on photometric units myself. Here are some good Wikipedia pages to look at. I figured it would be better I posted them as opposed to try and "interpret" them.

Candelas (the unit at the heart of it all)
http://en.wikipedia.org/wiki/Candela

Lumens
http://en.wikipedia.org/wiki/Lumen_(unit)

Base Photometry
http://en.wikipedia.org/wiki/Photometry_%28optics%29

Steredian (the base distribution evaluation for many of these units...kinda a "unit cone")
http://en.wikipedia.org/wiki/Steradian