I can't really answer your question in terms of lumens, but I did have to use my Surefire G2 for this application recently. I was confronted by 2 German Shephard size dogs while walking. I take my walks with my G2 in my left hand pocket, my Glock 19 on my right hip. The dogs advanced on me, growling with hackles raised. I pulled the light and fired it into the front dog's eyes, and he froze. As long as I kept it in his eyes, he froze. I think the G2 is rated at 65 lumens, so while one less bright may work, I know this one definitley does (on dogs, anyway), and at $35.00 it is one of the least expensive of the tactical type lights. Not sure I would want to stake my life on it when confronting a grizzly though.