AVAILABILITY OF SOLAR PHOTOSYNTHETICALLY ACTIVE RADIATION.

Photosynthetically active radiation (PAR) is a portion (0. 4-0. 7 micrometer wavelength) of the total radiation spectrum directly related to plant photosynthetic productivity. Experiments have been conducted to determine the correlations between the available hourly and daily PAR and total solar radiation. PAR was measured in micro-mol/s m**2 and total radiation was in W/m**2. Regression equations are presented in this paper for two purposes: (1) to show the predictability of PAR using available total solar radiation data, and (2) to provide empirical equations for estimating direct and diffuse PAR based on total radiation values.