One way of modelling and understanding the effect of light (mainly electric field) on an atom is to look at a simpler model consisting of three energy levels. In this model, we have simplified our atom to a transition between a state of 0 angular momentum ( J g = 0 ) , to a state of angular momentum of 1 ( J e = 1 ). This could be, for example, the transition in hydrogen between the 1s (ground state) and the 2p ( n = 1 , ℓ ℓ = 1 ) state.