MEASURING INCIDENT LIGHT ON GRAPE CLUSTERS USING PHOTOSENSITIVE PAPERAND IMAGE-ANALYSIS

Digital imaging and analysis was used to quantify and characterize the light exposure patterns of photosensitive paper tubes placed in repre sentative cluster positions in two grape (Vitis vinifera L.) canopies: a minimally pruned and a vertically trained canopy. Blue pixel values of the captured images had a negative correlation with the log of irr adiance from an integrating quantum sensor (r(2) = 0.9308). The spectr al response of the photosensitive paper was not measured. Histograms o f incident light distribution on individual paper tubes were developed using imaging software. Histograms were able to quantify the distribu tion of incident light on individual tubes and were clearly related to the tube's exposure in the canopy. Average population curves of pixel light distribution of 20 tubes in each canopy were able to differenti ate the typical cluster light environment in the two canopies. Tubes i n the minimally pruned canopy had a larger proportion of their surface exposed to irradiances > 50 mu mol.s(-1).m(-2) and 65% higher average irradiance than the vertical canopy. Image analysis of photosensitive paper appears to be a workable method to record the distribution of i ncident light in plant canopies and may have utility in a range of eco logical studies.