Recent advancements in fluid flow imaging techniques have made it possible to visualize local temperature in flows by observing the response of photoluminescent dye or particles to light excitation. This has sparked increased interest in exploring laboratory-scale density currents induced by temperature differences. However, unlike the commonly investigated saltwater-freshwater or turbidity currents, heat transfer through boundaries can occur, potentially influencing the dynamics of the density current. In this study, we utilize the dependence of the luminescence persistence time following pulse excitation on ambient fluid temperature of micrometric phosphor particles (YAG:Cr) to spatially and temporally resolve gravity currents produced by a lock-exchange flow. Notably, we introduce a novel inexpensive approach, which combine the use of LEDs and inexpensive high resolution CMOS sensors operated in a multi gate accumulation mode to extract temperature information with high spatial resolution. This simple method holds promise as it significantly enhances the accessibility of high resolution temperature imaging techniques for experimentalists. It can be applied to various thermal fluid experiments, to study for example thermal convection in fluid bodies.