VRayLight units

[CCS]

Interesting thread. Now, how do I adjust that number to get to real (inch/foot) units?

[Gijs]

Like I said, if Vray assumes always that 1 unit is 1 meter, it means that converting to inches means that you have to multiply by approx. 1550

[_jaro]

Gijs can you answer me this? I got my display unit scale set to "cm", my system unit setup is set to "cm" too .... when I create box 400 cm x 400 cm and create light U x V 400 cm x 400 cm my vray light is 2x bigger then my box when I look at it in top view. Why is that happening. Is it connected somehow with the issue that V-ray is representing units as meters? Because I don't understand it.

[Gijs]

When you create a light with U=1 and V=1, it means the light is 2 x 2 units. Not very logical, but this is just the way it is.

btw: I stated earlier that a bulb produces obout 10% light, but this is more the case for fluorecent tubes. I read somewhere else that the maximum lumens per watt a light can generate is about 685 lumens/watt.

See also this calculation:
http://hyperphysics.phy-astr.gsu.edu...on/lumpow.html

[_jaro]

I don't know if you came across to this http://en.wikipedia.org/wiki/Incande...and_efficiency , but this can come handy too
From what I have red till now ( just to make myself clear ) if I set the U and V size of light 20x20 cm - V-ray takes it as 20x20 m light source?

[dlparisi]

When you create a light with U=1 and V=1, it means the light is 2 x 2 units. Not very logical, but this is just the way it is.

Gijs: I brought this up in a thread under "Problems", http://www.chaosgroup.com/forum/phpB...ic.php?t=13438 , but no one seemed to comment on it. The problem is that vray uses the numbers (1,1) to determine the intensity, rather than the physical size. e.g.: a U=1 and V=1 vraylight matches the intensity of a "normalized intensity" switched light which makes sense, but you end up with a light that's 2 x 2 units.

Jaro: to determine the correct multiplier, vray only looks at the System Units. It doesn't care what the display units are.

[sv]

say your workingwith generic units and system units as millimeters, what would the calculation be for a 90watt bulb, 70mm x 70mm?

Please! All these calculations are bending my mind into a pretzel.

[Gijs]

Well, it isn't all that difficult. Consider the following:

If you are working in mm, multiply by 1000 x 1000
If you are working in cm, multiply by 100 x 100
If you are working in dm, multiply by 10 x 10
If you are working in inches multiply by 1/(0.0254^2) (approx. 1550)

If your bulb emits e% light, multiply the resulting number again with e x 0.01

The size in units of your light does not matter when normalize is checked, you 'only' have to take care about the units.

[_jaro]

Maybe I'm wrong, but when the efficiency of 100 W bulb is 2.6% the amount we set for V-ray light is 2.6, but when we consider 60 W bulb with its efficiency 2.1 %, I guess the amount we set for light is not 2.1 but 1.26. My speculation is based on what Vlado said. That V-ray light is concerning only output power, and for 60W bulb, with efficiency 2.1 % it means 1.26 W output power that is tranfered to light, rest is heat and so on.

[sv]

so for a 100W bulb in millimeters, the following is correct?

1000x1000x0.026 = 26000

So if the vray light was a sphere, i would set the vray light U size to about 75mm (roughly the size of the bulb), with a multiplier of 26000?

[_jaro]

Now it seems that those settings works only for PLANE V-ray light, when I simply switch to SPHERE (settings are same ) the render is completly burnt ( lots of light )

[dlparisi]

Just a guess, but maybe you need to divide the value by 12.56 (4*pi) since the surface area of a sphere is 4*pi*r^2.

[_jaro]

nope, this will not work, because I'm using normalize intensity ON, it doesn't metter what U x V size I have, when I divide Multip. by 4*PI it's not the same.
Now the thing with setting eaqul light is clear to me, but only with Norm. Int. chceked on, when I unchacked it, I don't know, how to set mult. to have same lighting.

[Gijs]

Jaro,

I don't have that problem when switching to a sphere. Or do you mean dome light?

[_jaro]

Gijs,
This is what I get when I simply swith from plane V-ray light to spherical V-ray light. Meybe I'm doing something wrong and it is not that simple. But can you tell me your set-up?