Pigments absorb light as a source of energy for photosynthesis

• The absorption spectrum indicates the wavelengths of light absorbed by each pigment (e.g. chlorophyll)
  

  • The level of absorbance can be quantitatively measured using a device called a spectrophotometer

• The action spectrum indicates the overall rate of photosynthesis at each wavelength of light
  

  • The rate of photosynthesis can be measured by either the rate of carbon dioxide consumption or the level of oxygen production

There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum

• Both display two main peaks – a larger peak at the blue region (~450 nm) and a smaller peak at the red region (~670 nm)
  

• Both display a trough in the green / yellow portion of the visible spectra (~550 nm)
  

Collectively, this demonstrates that photosynthetic pigments absorb red and blue light most effectively and reflects green light more than other colours

Absorption vs Action Spectra