<Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> An action spectrum is the rate of a physiological activity plotted against wavelength of light . It shows which wavelength of light is most effectively used in a specific chemical reaction . Some reactants are able to use specific wavelengths of light more effectively to complete their reactions . For example, chlorophyll is much more efficient at using the red and blue spectrums of light to carry out photosynthesis . Therefore, the action spectrum graph would show spikes above the wavelengths representing the colours red and blue . Engelmann split light into its components by the prism and then illuminated Cladophora placed in a suspension of aerobic bacteria . He found that bacteria accumulated in the region of blue and red light of the split spectrum . He thus discovered the effect of the different wavelengths of light on photosynthesis and plotted the first action spectrum of photosynthesis . </P>

How is the absorbance spectrum of pigments plotted in a graph