With the increasing establishment of greenhouses in conjunction with resource recovery projects (i.e., producing electricity by burning a low cost fuel), greenhouse facilities have access to low cost heat and in many cases electricity as well. In this regard we have been studying the production of spinach with the use of supplemental light.
The goal of the research was to establish the relationship between light and productivity and to also investigate the effects of light on tissue nitrate levels. The data indicate that an average daily PPF of 13-14 moles will provide enough energy to maximize the plant's relative growth rate. It was also found that supplemental HPS light with a PPF of 90 μmoles/m2/sec given over a 12h period will increase the total light received by a plant in mid-winter by about 50% and lead to a 10% decrease in leaf nitrate level.