Our lab has been investigating surfactant fluids with light-tunable rheological properties (i.e., “photorheological” or PR fluids). We recently reported a class of PR fluids based on wormlike micelles in water (JACS 129, 1553 (2007)). In this system, light caused a well-defined drop in viscosity due to a transition from long to short micelles. Here, we report an increase in viscosity due to light in a non-aqueous reverse micellar fluid. It is well-known that the phospholipid, lecithin can form reverse wormlike micelles in organic solvents like cyclohexane, upon addition of a small amount of water. These solutions consequently have a high viscosity. However, when we add a photoresponsive stilbene compound into the water phase the solution viscosity drops. When this sample is then irradiated with UV light, the stilbene undergoes a photoisomerization, and we observe that the viscosity reverts to a high value. These results are evidently due to the interplay between molecular geometry and reverse micellar structure. We will present results from a variety of spectroscopic, analytical and scattering techniques to elucidate the molecular and microstructural mechanism for our results.