Oxidized (blue) DPIP becomes colorless when it is reduced – that is, when it receives electrons. A diagram of the photosynthetic light reaction shows that water molecules are the source of these electrons. How is it that the DPIP was only able to receive reducing electrons from the photosystems (and ultimately from the water) when the lights were on, but not when the lights were off. Since the cuvette is mostly full of water, it is not the case that water is the limiting factor. Explain: what is the role of light energy in this system, and why does it make a difference in the reduction of the dye?