Study of photosynthesis using thermoluminescence (TL) requires precise control ofthe experimental parameters, particularly the excitation source and the sampletemperature. In this paper, we describe the design of an instrument that allowsautomatic control of various steps of the experiment and present illustrativeresults to demonstrate its versatility. The temperature sequence, the range andthe rate of cooling and heating of the sample can be set and controlled anywherebetween −150 and +90°C. The sample temperature can also be held constant atany temperature in this range to within ±2°C. Five light emitting diodes,covering discrete wavelengths from 470 to 660 nm and white light, areused for pulsed or continuous excitation. The ultra-high sensitivity andversatility of this instrument enabled two significant observations to bemade, being reported for the first time in this paper, namely that (a) TLoccurs in photosynthetic and non-photosynthetic materials even withoutpre-excitation and (b) TL also occurs during the sample cooling phase.