With sound you can create out of phase signals and they cancel out, this is not possible with light as it does not interact like sound does. If it was possible to create two light sources in that were exactly 180 degrees out of phase with each other and aim them at a common point (eg an isosceles triangle, the two points of identical angle are the light source, the 3rd point is the measurement point) regardless of the distance from the source to the point on which they combine the wavelengths would appear to cancel would they not? If they were of identical frequency and amplitude they would never depart from each other and would continue to appear "cancelled" at every point of measurement despite the photons still being there and containing energy. The light would not be coherent until the meeting point, this is the point upon which you would attempt to measure the frequency/amplitude. Would it appear to be zero? How would you actually produce an experiment like this, eg how could you lag the phase of a light signal, does it even make sense to attempt something like that? The reason for the question is I'm wondering if you could hide the fact a device/experiment is releasing energy by making all measurements appear null.