Field-scale photosynthetic efficiency depends on favorable light distribution throughout a crop canopy. Modeling experiments predict that an optimal canopy utilizes steep leaf angles to simultaneously reduce the (mostly wasted) solar load at the top of the canopy while increasing light penetration into the lower canopy. To test this idea, we built a simple mobile phenotyping system to measure reflectance and light penetration in 960 lines of bioenergy sorghum. We hypothesized that, after accounting for other environmental and physiological factors, lines that attenuate light more evenly across the depth of the canopy will produce more biomass by the end of the growing season. Our system consists of (1) paired spectroradiometers measuring incoming and reflected light, and (2) five line-quantum sensors at 0.5m height intervals measuring light penetration. Both components are mounted on an 18in wide hand-pulled cart to facilitate passage through 30in rows. Initial measurements indicate substantial variability in canopy light environment among lines. Top-of-canopy reflectance at 300 – 700nm ranged from 3% to 7% across lines, while light penetration at 50% of total canopy depth ranged from near-zero to almost 80% of full sunlight. Canopy reflectance and light penetration were not significant predictors of end-of-season biomass. However, we conducted initial measurements after canopy closure and expect a full growing season of measurements to yield greater predictive power. Our results point to a high level of variability in canopy light environment in energy sorghum, highlighting a potential target for improvement in this novel second-generation bioenergy crop.