Declining water resources and presence of large dairy and beef industry in the Southern High Plains are necessitating improving efficiency of forage production system to sustain irrigated agriculture in the region. In a typical annual forage production system, inter-row space is not used for a significant part of growing season leading to inefficiency in using resources like sunlight, water and nutrients. Protein rich legumes are broad leaf crops with tap root systems, which is different plant architecture compared to sorghum. Using legumes for intercropping may improve resource use efficiency, forage productivity and quality.  Field experiments were conducted to compare radiation use and radiation use efficiencies of forage sorghum [(Sorghum bicolor (L) cv. FS-5] grown alone or intercropped with lablab bean: (Lablab purpureus L. cv. Rongai) or pole bean (Phaseolus vulgaris L. cv. Genuine Corn Field) at the Agricultural Science Center at Clovis, New Mexico in 2008 and 2009. Line quantum sensors were installed in each treatment plots and two spot quantum sensors installed at 2m height were used to assess seasonal and diurnal patterns of light interception. Microclimate of the inter-row area was also monitored by installing temperature sensors and wind anemometers.  Adding another crop with the forage sorghum improved leaf area index (LAI) early in the season. The advantage gradually decreased and by 70 days after planting it was nonexistent. Increased LAI helped in increasing light interception (LI), which was 42-75% higher with intercropping compared to sole forage sorghum early in the season. But, intercropping advantage on LI lasted less than LAI, which suggests that the benefits of LI exists only when the overall LAI is not enough to intercept most of the radiation. In a few instances, intercropping reduced photosynthesis rate of forage sorghum, while rest of the time it was slightly lower but on par with the sole sorghum. Sorghum photosynthesis rates were always higher compared to those of legumes. Intercropping of legumes improved systems productivity early in the season (>30%). Significant contribution from legumes (25 to 40%) to the total biomass was mainly responsible for this. However, due to increased competition for resources, legume contribution and forage productivity benefits gradually reduced during the season. As a result the yield benefit of intercropping at harvest was -8 to 15%. Overall radiation use efficiencies of all three systems compared were similar. Legumes contained 2-3 times more protein compared to sole sorghum. Therefore, in spite of smaller and uncertain contribution to biomass, they influenced protein quality of forage.