FIGURE 6.

(A) Incident light use efficiency [LUE_inc, which is plant dry weight per unit of incident photosynthetically active radiation (PAR)]; (B) radiation use efficiency [RUE, which is plant dry weight per unit of incident radiation including PAR and far-red radiation (FR)]; and (C) intercepted light use efficiency [LUE_int, which is the plant dry weight per unit of canopy-intercepted photosynthetic photon flux density (PPFD)] of lettuce plants grown at three planting densities (23, 37, and 51 plants m^–2), with (52 μmol m^–2 s^–1) and without FR at 28 days after transplanting (DAT). Error bars indicate standard errors of means. None of these three parameters showed a significant interaction between FR and planting density (P > 0.25). For incident light use efficiency (A) and radiation use efficiency (B), effects of both FR [least significant difference (LSD) = 0.024 and LSD = 0.022, respectively, n = 3] and planting density (LSD = 0.030 and LSD = 0.027, respectively, n = 2) were significant (P < 0.001). For intercepted light use efficiency (C), planting density effect was not significant (P = 0.87) and FR effect was significant (P = 0.043; LSD = 0.15; n = 2). Data are means of two (n = 2) or three blocks (n = 3) each with four–six replicate plants.