[The_bluester (Paul)]

One way to put it would be that per pixel, per unit of exposure time (Call it per minute) you will get more signal on average out of a mono and filters due to collecting the wavelengths of interest on all pixels instead of one half or one quarter of them as is the case with a bayer matrix (Depending on the wavelength, half for green and a quarter of the others, with some crossover as a recent experiment I did showed)