Leaf Form & Function
During my dissertation work at UVM I developed a laser-based chlorophyll fluorescence microscopy system to study how direct and diffuse light are used by leaves. Using a custom built integrating sphere I was able to expose leaf surfaces to both direct and diffuse light and then observe the patterns of chlorophyll absorption and fluorescence. These experiments revealed that direct light penetrates deeper into leaves than diffuse light, and this difference in light penetration may play a role in decreased levels of leaf-level photosynthesis we observed in several types of leaves.
The figure above shows a transverse section through a single leaf illuminated with direct (A, C, E) and diffuse (B, D, F) light. Direct light penetrates deeper into leaves (most visible in the green wavelengths (C, D) than diffuse light, which appears to become trapped in the upper tissue layers. For more details, please see Brodersen & Vogelmann, 2010 in the journal Functional Plant Biology.