Photosynthetic Efficiency

The photosynthetic efficiency is the fraction of light energy converted into chemical energy during photosynthesis in plants and algae. Photosynthesis can be described by the simplified chemical reaction

H₂O + CO₂ + energy → C₆H₁₂O₆+ O₂

where C₆H₁₂O₆ represents carbohydrates such as sugars, cellulose, and lignin. The value of the photosynthetic efficiency is dependent on how light energy is defined. On a molecular level, the theoretical limit in efficiency is 25% for photosynthetically active radiation at the Chlorophyll-a absorbance peak (wavelength of 680 nanometers). However, photosynthesis is now known to occur up to 720 nm wavelengths (see Chlorophyll). For actual sunlight, where only 45% of the light is photosynthetically active, the theoretical maximum efficiency of solar energy conversion is approximately 11%. In actuality, however, plants do not absorb all incoming sunlight (due to reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels) and do not convert all harvested energy into biomass, which results in an overall photosynthetic efficiency of 3 to 6% of total solar radiation. If photosynthesis is inefficient, excess light energy must be dissipated to avoid damaging the photosynthetic apparatus. Energy can be dissipated as heat (non-photochemical quenching), or emitted as chlorophyll fluorescence.