The relative flux density of photosynthetically active radiation.

Published online
01 Jan 1977
Content type
Journal article
Journal title
Journal of Applied Ecology

Stanhill, G. & Fuchs, M.

Publication language


Measurements of global radiation using pairs of thermopile pyranometers, one of which was filtered with an RG8 hemisphere, were made under high insolation conditions in Israel and USA. For 0.5-h periods, when solar elevation was >10 deg , the relative flux density of photosynthetically active radiation eta was nearly constant at 0.49 plus or minus 0.05. Daily total values measured throughout one summer gave eta = 0.47 plus or minus 0.07 and monthly values of eta measured at 3 stations gave eta = 0.49 plus or minus 0.02. Results confirmed those previously reported for Europe and suggested that, within the accuracy with which it can be defined and measured, eta can be taken as 0.5 for periods of more than or equal to 30 min when the solar elevation is >10 deg

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