Commercial cadmium telluride (CdTe) photovoltaic (PV) modules from three different manufacturers were monitored for performance changes during indoor and outdoor light-exposure. Short-term transients in V oc were recorded on some modules, with characteristic times of ∼1.1 hours. Outdoor performance data shows a similar drop in V oc after early morning light exposure. Preliminary analysis of FF changes show light-induced changes on multiple time scales, including a long time scale. Multiple methods of measuring βV oc resulted in a range of values on the same CdTe PV module between -0.25%/C and -0.4%/C, possibly due to concurrent light-induced V oc transients and temperature changes. This paper highlights the need for rapid performance measurement of PV samples following light exposure and the possibility of incorrect results when using outdoor light exposure to collect values of βV oc for CdTe modules.