Crowd scanning is a super touchy subject and you need to do A LOT of math.. It's not so much the mw rating itself but the power density on the pupil and that changes based on distance and beam size scan speed and a zillion other factors... It's not something you want to do with a cheap projector that doesn't have interlocks, scanfails, beam blocks, attenuation zones and so on and so forth. It's illegal in many countries and not recommended. I would say if you need a mw number to keep under I'd say 5 mw being the absolute MAX for just random crowd scanning since a 5 mw laser is considered eye safe for brief exposure.. You would need a LPM to confirm it was not going over 5 mw and it would probably be too dim to get the effect you wanted.