Diurnal lizards often shuttle between exposed sunlit and shaded areas of their habitat, a behavior classically (and often solely) treated as a primary mechanism for thermoregulation. However, this behavior also affects exposure to other wavelengths of light important for fitness. For example, ultraviolet (UV) exposure stimulates endogenous production of vitamin D3 that is essential for calcium absorption, muscle function, and bone development, among other functions. Thus, both UV and thermal needs may drive behavior often attributed to thermoregulation alone. Despite these considerations, data on the effects of UV light on lizard behavior, including how UV needs may interact with (or override) thermal needs, are limited. Here, we capitalize on a laboratory environmental gradient approach to take an important step towards unraveling how variation in temperature, UV, and their interaction affect lizard behavior. We evaluated the behavior of 40 adult fence lizards (Sceloporus undulatus) in a laboratory environmental gradient with respect to four treatments: a temperature gradient alone, a UV gradient alone, a matched gradient of temperature and UV [gradients occur in the same direction], and an unmatched gradient of temperature and UV [gradients occur in opposite directions]. Depending on the treatment, we continuously recorded lizard body temperature (OMEGA logger) and/or UV exposure (UV Index, Arduino-based logger) for a 60-minute period per trial. Currently, our experiment is ongoing, but nearly completed. We expect our findings to provide novel insight into whether lizards regulate UV exposure and how that exposure influences their thermoregulation decisions. Our findings should also improve our ability to interpret apparent thermoregulation behavior by reptiles in both the lab and field.