We present theory to show that errors in lightning magnetic direction finding due to nonvertical source orientations are minimized by detecting the field from the lowest possible channel section. For 99 cloud‐to‐ground lightning channels photographed in Arizona, 45 exhibited a bottom few hundred meters within about 8° of the vertical, the standard deviation of the distribution of lower‐channel tilt angles being about 18°. These experimental results, coupled with theory, suggest that if a wideband gated direction finder is used, polarization errors due to nonvertical sources can be kept less than 1° for lightning beyo