Optimum utilization of photosynthetically active radiation (PAR) along with proper nitrogen management for sustainable rice production is still a promising management recommendation in order to increase profit for the low income rice farmers of the eastern India. The objective of this investigation was to relate the cumulative development of above ground dry biomass to cumulative absorbed photosynthetically active radiation (APAR) of 2 rainfed rice varieties (‘Lalat’ and ‘Gayatri’) with 3 nitrogen levels (50, 100 and 130 kg ha-1) under tropical monsoon climate of the region. Averaged over yeas and nitrogen level, radiation utilization efficiency in terms of above ground dry biomass (REUbio) of 1.88 (± 0.08) and 2.06 (± 0.09) gMJ-1 were recorded for the cultivar ‘Lalat’ and ‘Gayatri’, respectively. Higher dose of nitrogen increased the RUE significantly, averaged over years and varieties, mean values of it (RUEbio) were 1.68 (± 0.10), 2.04 (± 0.09) and 2.19 (± 0.08) gMJ-1 under 50, 100 and 130 kg ha-1 nitrogen respectively. The ratio of the latent heat flux to the available energy or evaporative fraction was found to be 79-82% in different cultivars and seasons. Partitioning of evapo-transpiration (ET) indicated that about 70-80% of seasonal ET came from transpiration.