Light gradients in plant tissue

In this paper we suggest a method for calculating light gradients in scattering and absorbing media. The method is based on the Kubelka-Munk theory and involves computational modeling of light fluxes in a multilayered object, when every layer satisfies the prerequisites of the Kubelka-Munk theory. The model also includes specular reflection that may contribute strongly to internal photon fluence rates for diffuse light. To illustrate the possible effects of light gradients, a cotyledon of Cucurbita pepo is described in terms of this model. It is argued that a number of results in in vivo spectroscopy cannot be correctly interpreted unless light gradients or optics in general are included in the discussion, i.e., the light flux at the site of the pigment has to be known. To outline the difficulties involved some methods of measuring light gradients or internal photon fluence rates are critically considered.