Why can't we see UV light?

Answer: Retina lacks UV photoreceptors

Retina lacks UV photoreceptors ✓ — Correct! Human photoreceptors (rods and cones) are sensitive to wavelengths ~380-700nm (visible light). UV wavelengths are shorter (<380nm) and don't trigger our cone/rod responses. Additionally, the lens and cornea absorb most UV, protecting the retina. Some animals (bees, birds) see UV—they have photoreceptors tuned to those wavelengths!

UV too weak to detect — Wrong. UV intensity isn't the issue. We lack photoreceptors that respond to UV wavelengths, just as we can't see infrared.

Brain filters UV wavelengths — Wrong. Brain doesn't filter UV. The retina simply has no photoreceptors that respond to UV wavelengths to generate signals for the brain.