  It is shown that the description of light beams in terms of the corresponding
photon quantum numbers elucidates the properties of these beams. In particular,
this description shows that the helicity quantum number plays the fundamental
role. This mode of description is applied to twisted and knotted
electromagnetic waves. We concentrate on the cases where photon wave functions
are eigenfunctions of one component of angular momentum. We discovered that for
knotted waves the eigenvalue of the angular momentum determines the topology of
knots.
