The transmission of light and total radiation by leaves

Abstract

In the course of work upon the colour composition of light in woods (Atkins and Poole 1931; Atkins, Poole and Stanbury 1937) it became evident that when the daylight factor (viz. the percentage of the external diffuse illumination) was low, there was always a marked difference between the spectral composition of the light in the wood and that of its source. This is obviously due to the fact that the proportion of the light transmitted by the leaves or reflected from leaves and branches is greater when the daylight factor is low. It became of interest therefore to measure the transmission of leaves. Such determinations might be carried out photographically with a spectrum projector or similarly using a thermopile to record the trans­mission. Alternatively a spectrophotometer might be used. It seemed simplest, however, to make the determinations photoelectrically in the open, using the cells, light filters and thermopile already used for measuring the light and energy in and around the woods.