Advanced Level Organic Chemistry: UV and visible light absorption spectroscopy - human eye pigments

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Doc Brown's Advanced Chemistry: PART 15.5 uv and visible light absorption spectroscopy - human eye

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses Spectroscopic methods of analysis and molecular structure determination

SPECTROSCOPY INDEXES  *  All Advanced Organic Chemistry Notes  *  [WEBSITE SEARCH BOX]

15.5.1 The origin of colour, the wavelengths of visible light, our perception!

15.5.2 uv-visible spectroscopy theory, spectrometer, examples of absorption & reflectance spectra explained

15.5.3 uv-visible absorption spectra - index of examples: uses, applications, more on the chemistry of colour

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The uv-visible light absorption spectra of the photopigments of the human eye.

The human eye has an amazing range of photopigments that respond to visible light photons.

uv-visible light absorption spectra photopigments of the human eye spectrum of red cones green cones blue cones rods wavelengths of maximum absorbance

Image from https://www.quora.com/What-if-our-eyes-could-see-beyond-the-visible-spectrum-Would-we-discover-more-colours

The uv-visible light absorption spectra of the photopigments of the human eye.

The photopigments of the eye are sensitive to the whole range of visible light photons and each individual pigment is sensitive to its own particular range of the visible spectrum - their own narrower range of visible light photons (listed below).

The cone cells are adapted to detect bright light and bright colours from three different type of photoreceptor proteins called opsins - examples of natural photopigments.

Cones contain opsins called iodopsin, porpyrosin and cynaopsin and the different proportions of them enable the three types of cones to be particularly sensitive to a narrower range of visible light photons. You can see there is quite an overlap in the three cone spectra.

The red cone cells are most sensitive green-yellow-orange-red photons,  λmax of 565 nm (yellow).

Iodopsin is particularly sensitive to red light - a greater proportion of it in a red sensitive cone cell.

The green cone cells are most sensitive to blue-green-yellow photons, λmax of 530 nm (green-yellow).

Cyanopsin is particularly sensitive to blue-green photons - a greater proportion of it in green cone cells.

The blue cone cells are most sensitive to violet-blue photons, λmax of 420 nm (violet) and detect lowest wavelengths of visible light.

The rods are most sensitive to violet-blue-green photons, λmax 495 nm blue-green (cyan).

The rods only contain the photopigment rhodopsin and are much more sensitive than cones and are adapted for us to see in dim light.

Rhodopsin is light sensitive substance formed from the protein opsin and 11-cis-retinal and can be triggered by a single photon.

Cone cells cannot detect colour by themselves; we perceive colour vision by the brain comparing signals from across the different cone types.

For more on the photochemistry of the eye see Cis/trans retinal - biochemistry of the eye

To add note on colour blindness?

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