Why can't we see infrared light?
Show answer & explanation
Answer: Photoreceptors don't detect it
Photoreceptors don't detect it ✓ — Correct! Human cone cells detect wavelengths ~380-700nm (visible spectrum). Infrared has longer wavelengths (>700nm) that don't trigger our photoreceptors. Snake pit organs detect infrared as heat. Some animals (goldfish, salmon) see near-infrared. We need special cameras to 'see' infrared by converting it to visible wavelengths!
Infrared doesn't reach Earth — Wrong. Infrared reaches Earth abundantly (sunlight is ~50% infrared). We can't see it because our photoreceptors don't respond to those wavelengths.
Absorbed by atmosphere — Wrong. Atmosphere absorbs some infrared, but the main reason we can't see it is that our cone/rod cells don't detect wavelengths beyond ~700nm.
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