If I understand correctly the term light field refers to a 5D concept - at each point in 3D space there are rays of light from all directions. Those directions use 2 more dimensions (e.g. $(\theta, \phi)$) and $2+3=5$. This could be called the 5D plenoptic function. I think at each point in this 5D space you have some kind of spectral intensity information. It could be RGB values or a complete spectrum, and would have units of (for example) power per unit area, per unit solid angle, per unit wavelength.
Is this just a name for a thing, or are there real, substantial mathematical things you can do with a light field? For example, if I know the Electric and Magnetic fields in a volume, I suppose could calculate the resulting light field in a straightforward way. But what can I actually DO with a light field besides market it?