Fluorescent wavelength shifting has been used to enhance the spectral response and AM0 conversion efficiency of several types of solar cells. Plastic fluorescent materials are useful for devices with a sharp cut-off in response, while ruby is suitable for devices with more gradual cut-offs. Efficiency improvements of 0.5 to 2 percentage points were measured on some cells, and greater improvements can be expected for optimized optical components. The optical efficiencies (light transmitted into the solar cell compared to light incident on the fluorescent sheet) exceeded 50% for the plastic sheets and 75% for ruby. © 1979.