What is photosynthetic radiation and why should it be measured to predict plant growth?
Photosynthesis and plant growth depend on the energy in radiation but only specific wavelengths of radiation cause photosynthesis. We have known since Einstein that one photon excites one electron (the Stark-Einstein Law), which starts photosynthesis. In 1972 a scientist named Keith McCree showed that a meter that counted the number of photons in radiation would more accurately predict photosynthesis than the previously used foot-candle meters. LI-COR (Lincoln, NE) started making meters to measure this radiation and scientists quickly switched to the new measurement system, which is called Photosynthetic Photon Flux (PPF). The energy in a photon is called a quantum so these meters are called quantum meters. A quarter century later, LI-COR has sold thousands of high quality meters but their least expensive quantum meter with sensor is $780. The high cost means that they are used only by scientists and large commercial growers. Smaller growers have continued to use foot-candle meters, wh
