Fig. 9

Relative spectral photon distributions (SPD) acquired under the combination of 1/4, 1/2, or full strength Rosco e-colour + plus green (PG) and Rosco e-colour + 0.15–0.60 neutral density (ND) filters. A–C 0.15 ND + 1/4, 1/2, or full strength PG. D–F 0.30 ND + 1/4, 1/2, or full strength PG. G–I 0.60 ND + 1/4, 1/2, or full strength PG. Data were normalized to the photon flux at 800 nm, and are presented as the average of relative SPDs acquired on 27 May, 30 May, and 12 June 2020 on clear sky or mostly sunny days between 13:00 and 14:00 h. The average relative PPF of blue (B), green (G), and red (R) light are inset in each panel (see Additional file 2: Table S6 for sample statistics); the average R:FR (655–665 nm/725–735 nm) and B:G (420–490 nm/500–570 nm) ratios are inset in each panel. Data collected under full sun were on average; R:FR = 1.15, B:G = 0.87, % Blue = 29%, % Green = 35%, and % Red = 36%. Red bars indicate 400 and 700 nm respectively, designating photosynthetically active radiation (PAR) between the red bars. Black lines represent the relative SPD of the layered filters, and green lines represent the SPD of the original PG filter