[en] We compare three laser induced fluorescence schemes for measuring velocity distributions of Ar-I 1s ₅ metastables in the presence of a magnetic field. In these three-level schemes, the 1s ₅ state is optically pumped to 2p ₂, 2p ₃, or 2p ₄ by sweeping the frequency of a tuneable CW laser over transitions in the visible range at 696.7352 nm, 706.9167 nm, and 714.9012 nm, respectively. Broadening in the fluorescence spectra is attributed to Zeeman splitting and saturation effects. We present measurements of spectral broadening dependence on injected laser intensity and describe spectral reconstructions that account for Zeeman splitting. For laser injection parallel to a background magnetic field, the separation of the Zeeman-split σ _± clusters is an effective, non-perturbative localized magnetic field diagnostic. We discuss the advantages of the three transition schemes and present the optimal transition for several applications. (paper)