Introduction The aim of the study was to evaluate rise in pulp chamber temperature after activation with different curing lights on bleached teeth in an in vitro study. The present study is an in vitro study with a sample size of 100. A total of 100 human extracted maxillary central and lateral incisors were collected and then randomly assigned into one control group and four experimental groups (n = 20). Material and Methods As many as 100 freshly extracted noncarious human maxillary central and lateral incisor teeth were used in this study. The access opening of all 100 samples were done to facilitate access to the pulp chambers for measuring the temperature. The samples were embedded into the additional silicone model, and uniform distance of 5 mm from tooth surface was taken for gel activation using different curing lights (LED, QTH, plasma arc, diode laser). The temperature inside the pulp chamber was measured using digital infrared thermometer. Infrared light of infrared thermometer was put on pulp chamber before the bleaching gel application (T₀) 1 minute after bleaching gel application (T₁). Later, there was changing of color of bleaching gel from dark red into green color when activated with different curing lights (T2). Statistical Analysis The temperature data obtained were analyzed statistically by one-way ANOVA and posthoc Tukey's tests. Significance level was set at 5% for all analyses. Results The mean and standard deviation (SD) values of rise in pulp chamber temperature after activation with different light sources were Group II (LED) 0.5 ± 0.466, Group III (QTH) 0.775 ± 0.229, Group IV (plasma arc) 1.26 ± 0.690, and Group V (diode laser) 1.355 ± 0.452. Conclusion Compared with other light-curing units, LED group induced lowest rise in pulp chamber temperature. Whereas, bleaching without light activation does not induce rise in pulp chamber temperature.