Although the amount of solar radiation received at roost sites used by bats has been speculated to be a factor driving roost-site selection and roost switching behavior, few studies have scientifically quantified and recorded it over time. We demonstrated through a field test how silicon-cell pyranometers, which are commonly connected to dataloggers and used in atmospheric studies to measure solar irradiance on a planar surface, can also be used to measure and record relative solar radiation levels at roost trees used by bats and other wildlife. Using commercially available pyranometers might not be feasible for many wildlife studies because they are expensive; we demonstrate how they can be built relatively simply and inexpensively, and calibrated with a commercial silicon-cell pyranometer.