Editing Light field (section)

===Illumination engineering===
Gershun's reason for studying the light field was to derive (in closed form) illumination patterns that would be observed on surfaces due to light sources of various shapes positioned above these surface.<ref>Ashdown 1993</ref> The branch of optics devoted to illumination engineering is [[nonimaging optics]].<ref>Chaves 2015; Winston 2005</ref> It extensively uses the concept of flow lines (Gershun's flux lines) and vector flux (Gershun's light vector). However, the light field (in this case the positions and directions defining the light rays) is commonly described in terms of [[phase space]] and [[Hamiltonian optics]].