Comparison of the NE-NLTE thick and non-equilibrium thin line formation of He i λ584 (left column) and He ii λ304 (right column). Upper panels: contribution functions (scale to the left) for thick formation (solid black) and thin formation (solid red). For context the temperature is also shown (dashed curve, scale to the right). Two additional scales are drawn in each of the two upper panels. The upper scale shows the optical depth at line center. The lower scale shows the optical depth for the continuum. Bottom panels: net rates into the upper level of the transition. Collisional processes are indicated by red lines and radiative transitions are indicated by black lines.