A weighted mean leaf-sun angle is defined as the ratio of the projection of sunlit leaf area on a plane normal to the solar beam to total sunlit leaf area. The former area may be measured photographically, the latter by application of a photosensitive chemical. The accuracy of the technique was assessed by numerical analysis over a range of leaf-sun angles, light flux densities and degrees of light saturation of photosynthesis. The maximum error was shown to be of order 16% which is considered acceptable in view of the simplicity of the technique. © 1973.
Smart, R. E., & Lang, A. R. G. (1973). A field method for estimating sun-leaf angles in productivity studies. Agricultural Meteorology, 11(C), 445–450. https://doi.org/10.1016/0002-1571(73)90089-7