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<i>Purpose</i>: Little is known about the effectiveness of bright white light therapy (BWL) for depressive symptoms in cancer survivors, many of whom prefer non-pharmacological treatments. The purpose of this study was to compare the effectiveness of BWL versus dim red light therapy (DRL) on depressive symptoms within individual cancer survivors using personalized (N-of-1) trials. <i>Methods</i>: Cancer survivors with at least mild depressive symptoms were randomized to one of two treatment sequences consisting of counterbalanced crossover comparisons of three-weeks of lightbox-delivered BWL (intervention) or DRL (sham) for 30 min each morning across 12 weeks. A smartphone application guided cancer survivors through the treatment sequence and facilitated data collection. Cancer survivors tracked end-of-day depressive symptoms (primary outcome) and fatigue using visual analog scales. Within-patient effects of BWL were assessed using an autoregressive model with adjustment for linear time trends. <i>Results</i>: Eight of nine cancer survivors completed the 12-week protocol. Two survivors reported significantly (i.e., <i>p</i> &lt; 0.05) lower depressive symptoms (&#8722;1.3 &#177; 0.5 and &#8722;1.30 &#177; 0.9 points on a 10-point scale), five reported no difference in depressive symptoms, and one reported higher depressive symptoms (+1.7 &#177; 0.6 points) with BWL versus DRL. Eight of nine cancer survivors recommended personalized trials of BWL to others. <i>Conclusions</i>: There were heterogeneous effects of three-week BWL on self-reported depressive symptoms among cancer survivors, with some finding a benefit but others finding no benefit or even harm. <i>Implications for Cancer Survivors:</i> Personalized trials can help cancer survivors learn if BWL is helpful for improving their depressive symptoms.