Abstract
Digital imaging and analysis was used to quantify and characterize the light exposure patterns of photo-sensitive paper tubes placed in representative cluster postions in two grape (Vitis `vinifera L.) canopies: a minimally pruned and a vertically trained canopy. Blue pixel values of the captured video images had a strong negative correlation with the log of irradience from an integrating quantum sensor (R2=0.9308). Histograms of incident light distribution on individual paper tubes were developed using imaging software. Histograms were able to quantify the spatial distribution of light on individual tubes and were clearly related to exposure in the canopy. Average population curves of light distribution were able to differentiate the typical cluster light environment in the two canopies. Tubes in the minimally pruned canopy had a larger proportion of their surface exposed to irradiences greater than 50 μmol s-1m-2 and 65% higher average irradience than the vertical canopy. Image analysis of photo-sensitive paper appears to he a workable method to record variation in spatial and temporal light in plant canopies.
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