This Demonstration presents diagrams showing the relative line strengths of the optical transitions between hyperfine-Zeeman states of the D1 and D2 lines in the most common isotopes of alkali-metal atoms (H, Li, Na, K, Rb, Cs). The total atomic angular momentum obeys , where is the electronic angular momentum and is the nuclear angular momentum.

The strength of the transition is proportional to the square of the electric dipole matrix element .

By successive application of the Wigner–Eckart theorem and angular momentum decoupling rules, it can be written in terms of Wigner 3j and Racah 6j symbols:

In the graphs the relative transition strengths are normalized such that the D2 line transition has a unit strength.