Comparison of the He i 1083 nm lower-level population assuming 3D radiative transfer (left-hand column) and 1D radiative transfer (right-hand column). Top row: cross-section weighted angle-averaged radiation field in a vertical slice at y = 11.9 Mm. Middle row: resulting lower level population of the He i 1083 nm line in a vertical slice at y = 11.9 Mm. Bottom row: column integrated lower-level population of the He i 1083 nm line, with the slice used in panels a)−d) indicated with a black line.