This study compares the effect of two N-of-1 trials on study compliance with an N-of-1 protocol and on satisfaction with participation in an N-of-1 trial. Using within-person analyses, the study also compares the effect of different types of light therapy on mood, fatigue, sleep, physical activity, and side effects within a mild to moderately depressed cancer survivor population. Ten participants will be randomized to the bright white versus dim red light therapy N-of-1 trial, while the remaining 5 participants will be randomized to a dim white versus dim red light comparator N-of-1 trial.

Fatigue or low energy levels, trouble sleeping and feeling down are symptoms that represent some of the most important concerns in cancer survivors, across a range of cancer types. Despite the impact of these symptoms on quality of life, previous studies have shown that few cancer survivors are receiving adequate treatment for these symptoms.

Light therapy involves the use of a light box (a box that lights up) in close proximity for a specified amount of time each day. There can be big differences in the way light therapy affects individual patients. Patients can learn whether this therapy is helpful to them by engaging in an N-of-1 trial. An N-of-1 trial is an experiment conducted with one individual (N refers to "number of individuals in the trial"). In an N-of-1 trial of light therapy, a patient can try light therapy to learn whether it is beneficial to them. All participants will receive two light boxes. The boxes will be labeled "A" and "B." Each light box will emit a different intensity of light. An app will send reminder notifications to participants' smartphones each morning to remind them which light box they should be using, depending on the week. They will be asked to use Box A or Box B each morning for 30 minutes per day for 12 weeks

The purpose of this study is to empower cancer survivors with symptoms of fatigue, trouble sleeping or who are feeling down to learn whether light therapy is helpful for them.

Inclusion Criteria:

• History of cancer (not including basal cell or squamous cell carcinoma, or carcinoma in situ)
• Current mild to moderate severity depressive symptoms (PHQ-8 score 5 to 19)
• iPhone user

Exclusion Criteria:

• Has not completed primary cancer treatment including initial chemotherapy, surgical resection, or radiation therapy
• Non-English speaking
• Severe depression (PHQ-8 score >=20) or active suicidal ideations
• Other severe mental illness that would preclude participation in a study that requires extensive self-monitoring, including depression with psychotic features, other psychotic disorder, bipolar disorder, severe personality disorder
• <6 months life expectancy due to cancer or other severe medical illness
• Other severe medical illness that would preclude ability to do daily self-tracking
• Unavailable for follow-up over the course of the 3 month trial