Whats the minimum mW/nm to see colored beams?

Whats the minimum mW/nm to see colored beams for green pens during the day, or in a room with light on, and how about when its dark?

well, it depends on the humidity, and how much 'stuff' is in the air. if you live in a humid place, you may be able to see a green beam in a lighted room at mws as low as 20. In normal conditions, its best to get at least 30-50mw to see a beam consistently. However, I have seen 5-10mw green beams when out in the pitch dark wilderness. I would say go with 40mw, or maybe evn 50. its safest bet!!!

The wavelength (nm) is also very important in terms of perceived brightness. The eye is most sensitive to green light (around 532nm). My 200mW red laser looks just as bright as my 45mW green laser.

-Tony