Two lights of the same brightness will never appear to be twice as bright as one of the lights, because perceived intensity is logarithmic. In other words, if you have a 500 lumen light, things won't appear twice as bright until you've got 2000 lumens, or four times the intensity of the original source. This is part of why I haven't invested in a second P7; I know I wouldn't be twice as satisfied with it/them as I am with my single light. I plan to hold off from another front light purchase until a 1000 lumen flashlight comes along in the $50 range.