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What happens to a photon after it hits the retina of my eye?
Herman D’Hondt
Sydney, Australia
Like everything else in life, the photon eventually becomes heat – an increase in entropy.
When the photon strikes one of the light-sensitive cells in the retina, it is absorbed by an opsin molecule. The colour-sensing cone cells use three different photopsins, one for each primary colour.
The rod cells use rhodopsin, which senses only light intensity, not colour. In all cases, the opsin absorbs the photon, which vanishes out of existence. However, its absorption by the opsin transfers the photon’s energy to…
