Dry matter production depends on the interception of radiation. In classical concept, the LAI is the principal growth index for determining the dry matter production as well as the yield of the crop. We hypothesized that sunlit leaf area index (L*) was a better index than the LAI for determining the dry matter production. Interception of PAR by mungbean [Vigna radiata (L.) Wilczek] varieties changes the sunlit leaf area index of the crop. This paper investigates the sunlit leaf area index (L*) and the interception of photosynthetically active radiation (PAR) by four mungbean varieties (V1-Pant Mung-5, V2-Bireswar, V3-RMG62 and V4-Sukumar) under three different dates of sowing (D1-15th February, D2-1st March and D3-15th March) and their relation with dry matter accumulation and leaf area index in the Gangetic plains of eastern India during the summer seasons of 2010 and 2011. The radiation interception increased with the age of crop and was found to be the highest when sown on 15th March. The interaction effect between interception of PAR and LAI showed that with the increase in LAI there was a corresponding increase in the interception of radiation which might have been due to the increased number and volume of leaves in the crop. 62.03 and 52.63% of the total variability were explained, respectively, by both dependent (interception of PAR) and independent sets (LAI). With L* and dry matter accumulation, it was seen that L* on 39 and 46 DAE significantly increased the dry matter production. It was also observed that L* increased when radiation was intercepted on 25 to 39 DAE. 67.58 and 79.55% of the total variability were explained, respectively, by both dependent (L*) and independent sets. It was evident that the mungbean might be sown during the first fortnight of March for better dry matter accumulation in this zone.