The surface temperature inside an optical engine both with and without heating the intake gas was measured. The temperature distribution was measured by a lifetime based phosphor thermometry using only three or 10 images recorded using a non-intensified high-speed CMOS camera by accounting for the pixel-to-pixel variation in the nonlinearity of the sensor. The luminescence from the phosphor was recorded at 40000 frames per second. A decay of luminescent intensity was represented by a mono-exponential function. The decay curves at various temperature conditions were fitted well to a quadric function, from which the decay constant at each temperature was obtained. The shot-to-shot standard deviation of the decay constant at uniform temperature conditions was 0.17〜0.33% and it varied ±0.15% with position, indicating that the pixel nonlinearity has a high nonuniformity. This technique was used to measure the temperature in an optical engine and it gave reasonable temperature maps.