Nifty thought, but the kind of measurement we need can't be done with RGB light producing devices or RGB light sensing devices. In fact, the knee-jerk-didnt-think-it-through criticism that will be raised will use the inherent limitations of RGB devices to try and discredit this instrument. This is why true monochromatic sources, diffraction gratings, and non-synthetic true pan-chromatic sensors are needed. 

(It will work, because we are exploiting bandpass filters built into the camera, so the criticisms aren't valid. But true monochromatic sources and pan-chromatic sensors will be needed to validate and measure the true response.)