Two pigeonpea (Cajanus cajan) cultivars GT-100 (determinate type) and BDN-2 (indeterminate type) were planted on three sowing dates (30 June, 20 July and 9 August) in 1993 and 1994. Pigeonpea sown on the earliest date attained the highest leaf area index (LAI), absorbed the largest amount of photosynthetically active radiation (PAR) and produced the highest total dry matter (DM). The differences in biomass and seed yield among sowing dates were largely ascribed to totals of PAR absorbed and dry matter produced, especially in the reproductive phase. The high LAI persistence and PAR interception, coinciding with the podding phase, appeared to be mainly responsible for the increased yield in early sowings. Radiation use efficiency decreased as sowing was delayed, but did not have much effect on DM accumulation in various phases nor on final yields. Although the extinction coefficient was not influenced by sowing dates, it was inversely related to leaf area index in both cultivars. Between the cultivars, the differences in biomass reflected the differences in PAR absorbed and DM accumulation, depending upon leaf area development and growth duration. The cultivar GT-100 had a higher seed yield and harvest index than BDN-2 due to more of the DM produced being partitioned into pods during the reproductive phase on account of its determinate growth habit. Early sowings of determinate cultivars could maximize both vegetative and reproductive growth, capture more light and produce more seed yields under rainfed conditions.