The final major component of the experimental set-up is the light source. In the literature, Xe or Hg lamps are typically used for irradiation . These light sources have a broad spectral distribution, which can be useful for simulating solar irradiation (although these lamps have emission spikes which are not found in the black body solar spectrum). However, during initial photocatalyst testing and quantum efficiency measurements, a more defined spectral distribution is typically useful and can simplify data analysis. For this reason, we have been using LED light sources, which offer relatively narrow (+/-10 nm for most wavelengths) emission, have a significantly longer lifetime than Xe or Hg lamps and their output power can be easily tuned through the applied current.