This is a question concerning the wave nature of light and the conservation of energy. Consider a prism that combines two sources of monochromatic, coherent (laser) light into one beam. The sources are adjusted so that the laser beams combine in phase resulting in constructive interference. So, the resultant beam has the same wavelength as the parent beams but it's electric and magnetic vectors have twice the amplitude. Now consider the same setup but with the one parent beam adjusted so that the beams combine 180 degrees out of phase, resulting in 100 percent destructive interference. The electric field vector of the first beam exactly cancels the electric field vector of the second beam and vice versa; the same is true for the magnetic field vector. It seems that at this point, with the two light beams perfectly combined 180 degrees out of phase that the resultant beam of light is effectively obliterated. If so, where does the energy go? How is the law of conservation of energy maintained when considering this system?