Photosynthetically active tissues, mainly green leaves, are the major component of forage growth and development. The amount of these tissues in a forage plant is influenced directly by cutting management, i.e. cutting frequency and stubble height. The normal recommendation is to cut (or graze) forage whenever it reaches a given stubble height. Brougham (1956) stated that the critical leaf area index (LAI) is reached when the forage canopy is intercepting 95% of the photosynthetically active radiation, and the forage is near its maximum growth rate without shading itself. Alternatively, the optimum LAI occurs when the forage reaches the maximum point of mass accumulation, indicating the time to start grazing or cutting. Generally, the critical and optimum LAI values are quite similar, but not necessarily the same (Brown and Blaser 1968). This trial evaluated the relationships among canopy height, LAI and light interception in 10 tropical grasses.