<P> where C H O is glucose ( which is subsequently transformed into other sugars , cellulose , lignin , and so forth ) . The value of the photosynthetic efficiency is dependent on how light energy is defined -- it depends on whether we count only the light that is absorbed , and on what kind of light is used ( see Photosynthetically active radiation ) . It takes eight ( or perhaps 10 or more ) photons to utilize one molecule of CO . The Gibbs free energy for converting a mole of CO to glucose is 114 kcal , whereas eight moles of photons of wavelength 600 nm contains 381 kcal , giving a nominal efficiency of 30 % . However , photosynthesis can occur with light up to wavelength 720 nm so long as there is also light at wavelengths below 680 nm to keep Photosystem II operating ( see Chlorophyll ) . Using longer wavelengths means less light energy is needed for the same number of photons and therefore for the same amount of photosynthesis . For actual sunlight , where only 45 % of the light is in the photosynthetically active wavelength range , 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 . </P>
what percentage of sunlight is captured by plants to convert it into food energy
3 to 6 %