Asked by: Richard O’Neil, Glasgow
Our most conspicuous encounters with lasers these days are with laser pointer pens. The first ones were red but these days other colours like green are available.
Our eyes’ sensitivity peaks at around the wavelength of green light. So, you could have a red and green pointer, both with a power rating of 1mW, but the green one would look about 30 times as bright.
Green light also scatters more in the atmosphere than red light does, which is why amateur astronomers often use green laser pens to point to features like planets or constellations in the night sky. The light scattering means you get a beam that’s visible high into the sky. It strengthens the impression that green lasers are significantly more powerful than red.