Spectra and photosynthetic photon flux density (PPFD) according to canopy position. Measurements were taken at midday at the flag leaf (FL), and the next three leaves (2L, 3L, and 4L). A, C, and E, Spectra for NPT variety IR65598-112-2 measured using a portable spectroradiometer and data here are expressed as arbitrary units. A, Top of the canopy (FL); C, 2L position; and E, 3L position. R:FR, Ratio of irradiance at 660 nm to that at 730 nm. B, D, and F, Decline in PPFD according to canopy position for the indica (IR72; ○) and four NPT varieties: IR655998-112-2 (□), IR65600-42-5-2 (▿), IR65600-129-1-1-2 (▵), and IR68544-29-2-1-3-1-2 (⋄). B and D, PPFD measured at 12 pm (i.e. sun directly overhead) and 3 pm, respectively. F, Values calculated as the percentage of that for the top canopy position measured at 12 pm. Means ± se, n = 15 to 20.