I have read in several places that monochromatic light cannot convey information; e.g. in http://www.mathpages.com/home/kmath210/kmath210.htm. it is stated that "in order to actually convey information, a signal cannot be a simple periodic wave". But doesn't all light have the energy hf? And doesn't that mean that we can effect a change, for example by Schrödinger's equation? And isn't every change a piece of information? So why wouldn't a monochromatic pulse of light convey information?