intensity property
How bright this light is, in the engine's own unit — see Photometric for what that unit is worth in lumens, candela and lux.
Dimensionless on purpose, and it stays that way: the shaders multiply it by an attenuation and a tone curve maps the result, so putting a physical unit in here would mean every existing scene's numbers changing meaning. Photometric converts into it instead, which leaves a hand-tuned lamp and a lamp off a datasheet side by side in the same field.
Implementation
double intensity;