Photosynthesis was measured with narrow band light at 18 wavelengths in the interval 406–720 nm. The bandwidth was
10 nm in the interval 460–720nm and 20nm at 406, 427 and 445 nm. The leaf was illuminated by two 250W halogen lamps,via a 4-armed fibre optics light guide. Lamp 1 provided a continuous broad-band background light (40molm−2 s−1), of which the halogen spectrum was filtered with a heat filter and a filter to convert tungsten halogen light to day-light (Lee filters, Hampshire, UK). Narrow band light was obtained by placing a narrow band interference filter between lamp 2 and an arm of the fibre optics. The light from the two lamps was projected fully mixed on the leaf surface. At each wavelength, photosynthesis was measured at the background light plus 0, 30 or 60molm−2 s−1 narrow band light, after a 3-min exposure to 100molm−2 s−1 of broad-band light. This low light intensity is usually adopted in research on spectral dependence of photosynthesis in order to count on a reliable light response,since, at this level, the relationship between photosynthesis and light radiation is supposed to be linear.
Photosynthesis was measured with narrow band light at 18 wavelengths in the interval 406–720 nm. The bandwidth was10 nm in the interval 460–720nm and 20nm at 406, 427 and 445 nm. The leaf was illuminated by two 250W halogen lamps,via a 4-armed fibre optics light guide. Lamp 1 provided a continuous broad-band background light (40molm−2 s−1), of which the halogen spectrum was filtered with a heat filter and a filter to convert tungsten halogen light to day-light (Lee filters, Hampshire, UK). Narrow band light was obtained by placing a narrow band interference filter between lamp 2 and an arm of the fibre optics. The light from the two lamps was projected fully mixed on the leaf surface. At each wavelength, photosynthesis was measured at the background light plus 0, 30 or 60molm−2 s−1 narrow band light, after a 3-min exposure to 100molm−2 s−1 of broad-band light. This low light intensity is usually adopted in research on spectral dependence of photosynthesis in order to count on a reliable light response,since, at this level, the relationship between photosynthesis and light radiation is supposed to be linear.
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