Light has been previously shown to play a role in the emission of mercury from soil; however, the mechanisms involved in this process are not well understood. In an effort to identify the wavelength of light that dominates this process, we conducted extensive laboratory studies of soil mercury flux using a dynamic flux chamber. Mercury fluxes were measured at constant temperature in the dark, under full spectrum radiation (λ = 320--700 nm) and under various radiation bands including 410--700 nm radiation, 320--580 nm radiation, and 320--380 nm radiation. Soil mercury emissions under full spectrum radiation were significantly elevated over dark fluxes in all trials. When UV light was removed from incident radiation (the λ = 410--700 nm condition), fluxes were not significantly different from dark fluxes in two of three trials. Soil fluxes under 320--580 nm radiation and 320--380 nm radiation were significantly elevated over dark fluxes in all trials and were related to radiation intensity in the UV region.