units for reflectors and diffusers

[Abdul Rahman Jamous]

What are the units that cinematographers use to describe the power of a reflector or a diffuser? 

[David Mullen ASC]

There is no standard units of measurement for that.  I suppose some gel manufacturers might list transmission factor for diffusion gels like they do for color gels, but maybe not. It's hard to quantify because you can have a hot spot in a bounced or diffused light.