Action Spectrum. Action spectrum is a curve which shows relative rates of photosynthesis at The graph of the action spectrum indicates that the maximum photosynthesis takes place in the blue and red parts of visible light. 

Wave length of light in nm Graph of Action Spectrum

Absorption Spectrum. Absorption spectrum is a curve which shows the amount of light of different wavelengths absorbed by a substance or pigment. The absorption spectrum of two chlorophyll (chl “a” and chl “b”) and carotene shows that maximum light absorbed is in the blue and red wavelengths.