[Question]:IES profiles and performance/memory

IES profiles are really great to have in Rocket, but couldn’t find anything about their performance hit or memory consumption. I know IES profiles are “just” short text files, but have no idea how they are used in UE, if they converted to some kind of texture projection or not.

Simply said, when we would want to use IES by default on all lights, is there anything we should be aware of performance or memory wise?

Does the number of “values” in IES profile influence performance/memory?

Is using spot lights with IES cheaper then using point lights with IES?

Thanks.

IES files get converted to a small 1d texture (open in texture properties to see it, we might change the texture format) and a multiplier.
Lights using the IES make an additional lookup into this texture - a few math instructions are needed.
Light using the IES cannot be combined and rendered with the tile based lighting (same for shadow casting, lightfunction using).
Spot lights are slightly cheaper than IES spot lights, point lights with an IES making them sport lights are much slower (compute pointlight and then mask the sport area), IES are cheaper than using lightfunctions.

We intend to optimize IES lights to also work for tile based lighting (this is where the 1d texture comes in handy - it can be easily combined into a 2d texture).

Thanks a lot for the detailed explanation.

For those of us less technically inclined, this means yes there is a performance impact but how much of one? If as the OP said, you were to add a light profile to 20 lights in your scene, would this impact performance heavily? Moderately? Slightly?