The parameter value ˛ (quantum efficiency in mol electrons per mol photons) was set at the value as derived for each wavelength from the LICOR 7000 measurements. The measurements used to calculate ˛ were under non-photorespiratory conditions. Gross photosynthesis per wavelength was calculated for a rose crop having a leaf area index (LAI) of 3, receiving 30molm−2 s−1 of diffuse photosynthetically active radiation at the top of the canopy, at a CO2 concentration of 350ppm and an air temperature of 22 ◦C.