Objective: The aim of this study was to assess the dental bleaching efficacy of 37.5% hydrogen peroxide (HP), with and without light activation, in HP-exposed and unexposed areas. Method: 28 bovine teeth were selected and divided into two groups (n = 14). Crowns were detached and stained with tea. The gingival half was covered with a gingival barrier. In the incisal half, 37.5% HP (Pola Office+, SDI) was applied three times, with a 1-week interval between applications. In HP-A group, the bleaching agent was activated for 3 min with a LED lamp. No light activation was applied in HP-N group. Dental color variation was determined through a spectrophotometer in both halves. Statistical analysis between groups was performed with an ANOVA test, and intragroup differences were evaluated, with an ANOVA test for paired data, with a significance level of P 0.05. Results: An increase in lightness and a decrease in chroma were found in both groups and halves. No significant differences in ΔE between groups (P > 0.5) were detected in the incisal half. After treatment, a significantly higher ΔE was found in the gingival half for HP-A group (P 0.05). For the same group, a significantly higher bleaching effect was found in the gingival half, compared with the incisal half (P 0.05). Conclusions: LED activation did not have a significant effect in terms of bleaching in the incisal half, but increased clearance in the gingival half. Clinical relevance: HP light activation does not significantly increase the whitening effect, but it can improve the bleaching diffusion to areas where it has not been directly applied.