The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao:
[5]
Starting with the solar spectrum falling on a leaf
47% lost due to photons outside the 400-700 nm active range (chlorophyll utilizes photons between 400 and 700 nm extracting the energy of one 700 nm photon from each one) [Photosynthetically_active_radiation]
30% of the in-band photons are lost due to incomplete absorption or photons hitting components other than chloroplasts
24% of the absorbed photon energy is lost due to degrading short wavelength photons to the 700nm energy level
68% of the utilized energy is lost in conversion into d-glucose
35--45% of the glucose is consumed by the leaf in the processes of dark and photo respiration
Stated another way:
100% sunlight --non-bio-available-photons-waste-47% leaving-->
53% (in 400--700nm range) --30%-of-photons-lost due to incomplete absorption leaving-->
37% (absorbed photon energy) --24%-lost-due-to-wavelength-missmatch-degradation-to-700nm-energy-level leaving-->
28.2% (sunlight energy collected by chlorophyl) --32%-efficient-conversion-of-ATP-and-NADPH-to-d-glucose leaving-->
9% (collected as sugar) --35-40%-of-sugar-is-recycled/consumed-by-the-leaf-in-dark-and-photo-respiration leaving-->
5.4% net leaf efficiency
net efficiency of a leaf at 25°C is about 5%
many plants lose most of the rest of this doing things like growing roots
most crop plants store ~0.25% to 0.5% of the sunlight in the product (corn kernels, potato starch, etc)
sugar cane is exceptional in several ways to yield peak storage efficiencies of ~8%.
Photosynthesis by D.O.Hall & K.K.Rao says that photosynthesis increases linearly up to about 10,000 lux or ~100 watts/square meter before beginning to exhibit saturation effects. Thus, most plants can only utilize ~10% of full mid-day sunlight intensity. This dramatically reduces average achieved photosynthetic efficiency in fields compared to peak laboratory results. Real plants (as opposed to laboratory test samples) have lots of redundant, randomly oriented leaves. This helps to keep the average illumination of each leaf well below the mid-day peak enabling the plant to achieve a result closer to the expected laboratory test results using limited illumination.
