Calculating and reporting key light ratios for plant research

Recent advancements in light-emitting diode (LED) technology have provided excellent opportunities to precisely control the spectral output of lamps and to study the resulting impacts on plant growth and development. Plant scientists often use light (or radiation) ratios to compare different light sources and assess their potential effects. For example, based on the average plant response to photosynthetically active radiation, the red:blue ratio can be used to assess the effect a particular light source may have on plant growth and/or morphology. In addition, many lighting companies market their products as having an optimal 'light recipe' that often includes a combination of specific wavelengths and specific light ratios, for example '4 to 1 red/blue'. However, the scientific literature does not provide exclusive definitions of the key wavebands that are used to calculate these ratios. For example, red light is sometimes identified as light with a peak wavelength of 660 nm, and other times as all radiation across the 600-700 nm waveband. As a result, calculated light ratios can have very different values, making comparisons among experiments challenging. We used spectroradiometer data (280-800 nm) to determine key light ratios for sunlight and various electric lamps (INC, CFL, CMH, HPS, and LED). The calculated ratios included red:blue, red:green, green:blue, red:far-red and ultraviolet:blue. Depending on the range of wavelengths used for each waveband, calculated values for the light ratios will be different. This demonstrates the importance of standardized definitions for key wavebands and using such definitions will hopefully contribute to an easier interpretation of light ratios that are reported in the literature. At a minimum, we hope to convey the importance of adequately presenting information about the specific waveband ranges used to calculate light (or radiation) ratios.