Physics of Emissive Lights and UI communicated values of Lights

Rendering
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what is the current physics/maths of the falloff of emissive lights? is there any way to control it? like for instance rectangular light? i have not found anything but it seems its something like physically related inverse square but would just like to know.

i also noticed that it actually makes a difference in which size the geometry is rendered, so the values of the available light intensity parameters obviously somehow correspond to the actually size in relation. maybe it would make sense to communicate more relatable values then, like watt or lumen instead of some, arbitrary intensity, or multiplier values which suggest that the values could be scalable.

the same for other lights actually here the values also correspond to size and could have a naming which relates to real world values.

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This all makes a lot of sense, I will write these up, thanks.
As for the Emissive material: yes this is inverse square

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It won’t be easy to express though, since in Cycles one unit equals one meter. But if you have a Rhino mm template and you make your light bulb 10cm in size you’ll have a huge surface from Cycles perspective.

Some info on Cycles lights: Light Objects — Blender Manual and Emission — Blender Manual

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@nathanletwory I’m not sure if I understand. If a lightsource would emit a certain amount of light (lm/sqm) then the chosen unit setting shouldn’t make a difference imo. What am I missing?

edit: reading the article, I understand current values represent Watts?

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In Rhino if you have a box 1mmx1mm then in Cycles it is 1 unit x 1 unit meaning 1m x 1m.

A lamp of 10cm heigh in a Rhino mm file will be 100 units high from Cycles perspective.

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I’ve added RH-72012 wish: set Light intensity independent from its size

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thanks Gijs, its non public though so i did not manage to read it up

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I’ve opened it now.
-wim

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