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A new quantum sensor for measuring photosynthetically active radiation (PAR) was designed using a gallium arsenide photodiode. This sensor is cheap and effectively measures radiation between 400 and 700nm without any filter, which allows both high output level and easy manufacturing. A comparison with two other commercially available quantum sensors (Li-Cor and Macam sensors) was made. The sensor des- cribed here was less sensitive than the two others both in the blue and far-red parts of the spectrum. Its maximum sensitivity is near 600nm. However it was shown, under natural light and several artificial light sources, that the results given by the three sensors were very similar. Nevertheless some problems could arise with monochromatic light sources such as sodium lamps whose spectrum is mainly composed of radiation between 570 and 620nm. This study also shows that gallium arsenide sensors are suitable for PAR measurements under canopies.
J. Y. Pontailler (Mon,) studied this question.