The instructors school I used my M-4 in was all daylight, bright and sunny except for one day. When we left the acadamy building for the range I turned it on, bumped up the brightness setting about 4 levels from the default power on setting, and it was outstanding. It still had a few more levels to go. I never turned it off, just let it time out. Used the same batteries for all week, they were in the sight since I purchased it. (I changed them after the school, they're fresh now) I have had no problems with the visibility of the rectile outdoors, indoors, in dark streets,etc.