Scalings and Lights

Hi. In Blender cycles, I have a scene which I want to scale everything up by 5x, but the entire scene will turn dark due to scaling the lamps as well. Is there a way to fix it or calculate the lamp strength values for the enlarged scene so that I can have the same lighting previously? It seems like multiplying the strength of every lamp by 5 doesn’t give the same results as before.


that’s a good question. Ideally the light intensity falloff should be adjusted, but the perceived ray length will always be 5 times greater, so the light won’t behave the same… ideally there should be a distance multiplier in the light falloff node.

I fiddled a bit though and it seems a factor of 25 in the light intensity does nicely.


To get same intensity at 2x the distance you must square the light intensity. The inverse square law of light states that and in Cycles it works that way by default. It is not due to ray length being different but because rays diverge in space.

Keep in mind that sun lamp does not need scaling as it does not have any falloff at all due to rays being parallel to each other. The same effect is used in lamps with egg crate diffusers that try to form the light so that rays are more parallel and the irradiance on a surface does not change so much when moving the lamp.

Thanks for the replies! I get it now. Somehow the inverse square law of light didn’t come to my mind.

One more question. What value should I put for ‘smoothness’ in the light falloff node for it to be physically accurate? I assume I use the quadratic falloff because of the square law.