between action spectrum at crop level differed even more from that at the leaf level. The action spectrum of green light (520–570 nm) was 67% of that of red light (680 nm) at the leaf level, while this was 78% at the crop level (Fig. 4). So an absolute increase of crop vs. leaf of 11% at green light is calculated, while for the whole PAR spectrum an increase of 6% (i.e. the surface area between leaf and crop curve in Fig. 4) is calculated per incident photon.