<p>This study evaluated color change, hydrogen peroxide (HP) penetration into the pulp chamber, gel properties, and temperature variation during in-office bleaching with 6% HP combined with different light sources. Sixty extracted sound premolars were randomly allocated into three groups (n = 20): (1) 6% HP without light activation, (2) 6% HP activated by violet light, and (3) 6% HP activated by blue light. Bleaching procedures followed the manufacturers’ recommendations. HP penetration into the pulp chamber was quantified using UV-Vis spectrophotometry. Color change was assessed with a digital spectrophotometer (WI_D). Initial and final HP concentration and pH were determined by titration and a digital pH meter, respectively. Temperature variations during light activation were measured using a thermocouple. Data were analyzed using ANOVA and Tukey’s test (α = 0.05). The 6% HP + violet or blue light groups exhibited lower HP penetration compared with the 6% HP group (<i>p</i> = 0.02). The 6% HP + violet light group showed higher whitening values compared with the other groups (<i>p</i> &lt; 0.001). The 6% HP group retained a higher HP concentration (<i>p</i> = 0.001). Light-irradiated groups exhibited higher temperature variation and greater pH reduction compared with the 6% HP group (<i>p</i> &lt; 0.001). The violet-light protocol combined with 6% HP resulted in higher whitening values and reduced HP diffusion into the pulp chamber. However, light activation was also associated with increased temperature variation and slight pH reduction, which should be considered when interpreting the biological safety of these protocols.</p>