Vlado wrote:
"…What is confusing is that there are two different quantities here - the (electrical) power consumed by the source, and the power of the light that is emitted. These are *different* things. What I wrote for the VRayLight concerns the emitted light power, not the electrical consumption of the source. A 60 watt bulb consumes 60 watts of electrical energy, but it certainly does not emit all of them as light power.
Best regards,
Vlado"
The Watt and Watt/m^2 -- radiometric units (at context of the light), and Lumen -- photometric units. Usage of photometric values is more suitable.
There is a scaling factor for conversion of the value in Watts to the value in Lumens in Physics.
Most is often mentionned following scaling factor -- 683 lm/W.
“…Monochromatic light 555nm with radiant intensity of 1 Watt = 683 Lumens.
OR
Monochromatic light 555nm with radiant intensity of 1 Watt/sr= 683 Candela…”
What value of scaling factor follows to use with VRay?
well then. the new energy saver lights i just put all though my appartment burn 7 watts of power but have the brightness of a 60 watt bulb. so looks like your watts per lumen theory just went clear out the window.
It’s the same thing… “radiant energy” is also measured in joules, and “unit of time” is, of course, second.
I believe with all these units stuff, you have to start backwards - e.g. determine what units you get in the final image pixels, and determine the rest from there… In V-Ray, by default, the image pixels represent average radiance over the pixel’s area. Radiance is measured in power per unit area per unit solid angle (=amount of energy per unit time per unit area per unit solid angle). Radiance is closely related with the apparent brightness of a surface, and it is radiance that our eyes register. However, it is *not* what a photographic image represents, since a photographic plate has actual dimensions, and it is exposed for an actual period of time.
Anyways, fixing your image units allows you to figure out what values to type in the lights.
Continuing this line of though, you may ask: what actual units does V-Ray produce on the screen (e.g. what is the energy unit, the time unit etc)? The answer is: whatever you choose them to be. This is like asking what units you see with your eyes.
I think vray already uses this ratio. Setting a vray light to 1 watt and then switching to lumens changes the value to 683. Same for watt/sr and Candela. Is this what your asking?