Is there any information about the nature of light that can be used to narrow down the limited shapes it could be, or logicaly dictate the shape it must be due to its known nature?
Per quantum theory, 'light' is comprised of particles called photons. Photons are described by waves. These waves have a particular direction of propagation with amplitudes along that direction. As such, the basic 'shape' of light is that of a one-dimensional line.
Or is it? This view is based on the 'light moves in straight lines' assessment (or, generally, along geodesics, which are 'straight lines' that may actually be curved) which is empirically satisfactory. However, underlying theory is less happy with this view. In quantum field theory, the photon moves from the point of creation to the point of annihilation via every possible path. The contributions of these paths attenuate quickly with deviation from the straight line, so ignoring negligible terms, I guess the photon is kind of an elongated egg shape. (See attachment)