From Photons to Food

The four most environmentally sensitive inputs to our food production system are sunlight (photons), water, nitrogen, and phosphorous. Sunlight is the limiting input if food is grown with electric lighting. Here I review and analyze radiation capture, the quantum yield of photosynthesis, respiration efficiency, and carbon partitioning efficiency to show that a mole of photosynthetic photons can yield up to a gram of dry mass of food, regardless of the source of photons.   Assuming an electric cost of $0.10/kWh and our most efficient electric lights (6.1 moles of photons/kWh), the economic value of summer sunlight is $400,000 per acre over a 100 day growing season.  Winter sunlight during the darkest 60 days of the year is worth about $40,000 per acre.  These values drive the comparative costs associated with indoor/outdoor food production. I also compare water, nitrogen and phosphorous recovery to show the wide variation among indoor and outdoor food production systems.