Treating the moon as an ideal, bright Lambertian reflector, I was trying to compare its efficiency as a light source to an equally-sized flat sheet of drywall. It's pretty straightforward to set the problem up, but I'm not so sure of my calculus. I got that the flat sheet of drywall would provide 50% more illumination in full moon conditions as compared to the spherical moon, treating both of them as smooth, diffuse lossless reflectors. I wonder if anyone wants to second-guess my math?
I talk about the problem on my blogsite here.