Photosynthesis is the process by which green plants trap light energy and use it to make carbohydrates.
When light strikes a leaf, some (12 per cent) is reflected, some (5 per cent) is transmitted through the leaf and the rest (83 per cent) is absorbed by the pigments within the chloroplasts.
Pigments are chemicals found within the chloroplasts which absorb light energy and convert it to chemical energy. The principal pigments are chlorophyll a and b - they mainly absorb light in the red and blue wavelengths of light.
Plants also contain carotenoids (carotene and xanthophyll) which absorb light from other regions of the spectrum and pass the energy on to chlorophyll a.
The absorption spectrum (graph A) shows the wavelengths of light absorbed by the different pigments in a leaf. The action spectrum (graph B) shows how effective the different wavelengths of light are at photosynthesis.
Having multiple photosynthetic pigments increases the range of wavelengths of light that the plant can absorb and so increases the level of photosynthesis.