The product of these three terms expresses the <strong>"monochromatic
current yield"</strong> - that is, the percentage of photons of a specific
wavelength (or colour) that will result in an electron reaching the
counterelectrode.  This essentially shows how much current will be
obtained at different wavelengths.

This equation shows one reason why, even though the light
harvesting efficiency of the dye is nearly 100% at most visible
wavelengths (see FIG. 3), the efficiency of the cell is far from 100%. 
Essentially, there are other losses involved.

Read the tips about the other three terms to see what they mean!