Comparison of relative illuminance, relative photosynthetic photon flux and relative cumulative amount of global solar radiation in apple [Malus pumila] tree canopy

Relative light intensities in an apple (Malus domestice Borkh.) tree canopy were determined by measuring light quantity: Photometrically (illuminance, lx), radiometrically (radiation, W. m-2), and in quantum terms (photosynthetic photon flux, mumol. m-2. s-1). There was a strong positive correlation between relative illuminance and relative photosynthetic photon flux, measured on an overcast day. Relative photosynthetic photon flux was, however, 6.0 % higher than relative illuminance. A strong correlation was also found between relative illuminance and relative cumulative photosynthetic photon for one day; the latter was higher by 6.7 % on an overcast day and 6.8 % on a clear day. There was a strong positive correlation between the relative cumulative photosynthetic photon and the relative cumulative amount of global solar radiation for one day, while that of relative cumulative photosynthetic photon was 11 % lower than relative cumulative amount of global solar radiation