Why does a green point laser look brighter than a red one?

The human retina is most sensitive in the green spectral range around 555 nm – that is the peak of the eye's spectral sensitivity. Green laser light at 520 nm sits close to this peak, while red light at 650 nm sits at the edge of visual sensitivity. Specifically: a 5 mW green point laser looks visually about as bright as a 25–35 mW red point laser. Practical effect: at equal perceived brightness, green gives you a lower laser class – Class 2 instead of Class 3R for red. This simplifies safety measures significantly. Trade-off: green laser diodes are more expensive and more temperature-sensitive than red ones.