Your proposed constant is very interesting indeed.
It will be a great plus to establish a link of the photosynthetic solar constant PSC with other biophysical parameters of vegetation measured with remote sensing methods (data acquisition via local/airborne/satellite equipment). This way you could validate it and find new interdisciplinary applications.
I would start by approaching the specific plant species demand for solar radiation related to plant physiology, adaptation strategies, geographical location/abundance, biomass, geodistribution, elevation, competition, and relating the constant to specific plant bioenergetic demand.
In that sense, I propose to use chlorophyll fluorescence fast induction technique, as a universal method for calculating vegetation bioenergetic requirements based on the photosynthetic solar constant and state-of-the-art photosynthesis models.