I've seen the term being thrown around a lot lately when I read up on engines with their new PBR pipelines. Quite a few of them are saying that they now specify their light intensities in Lumens. I know that that is a term referring to output from real-world light source, but that's the extent of my knowledge.
My questions are:
1.) How do they pertain to lights in shaders?
2.) Is there a specific formula for calculating the light intensity from them?
3.) Am I just over-thinking this, and Lumens is just another name for the light intensity scale value?
Any help would be most appreciated. Thank you.