Hey everyone, I'd like to recreate Vray's light meter in Houdini for use with Mantra and Redshift. I guess the best place to start would be calculating the lumens at a particular point on a surface. Would anyone have any suggestions as to how to do this?

Mantra doesn't use absolute units for light intensity, all units are relative to the final pixel intensity. Physical effects such as sensor sensitivity (ISO), exposure duration, and aperture have been factored out. So asking to quantify light using an absolute metric would first require quantifying the other physical factors. It can be done, but to me sounds like needless complexity. I can see why you might want it if you must match certain real world measurements though.