why is it easy to see the beam of a 100mw green laser when it isn't too dark but not a red 200mw when it is?

Answer 1

I think eyes are actually more sensitive to red. A 200 mW laser is pretty powerful. If you're having trouble seeing it, you must be talking about projecting a dot onto an object at great distance. Be more clear. If so, for a given aperture, a green laser beam will spread out slow and produce a smaller dot due to its shorter wavelength. That means more mW per unit area and, therefore, greater contrast with ambient lighting. The eye needs contrast to see.

Answer 2

It's because our eyes are more sensitive to green light than red light.