Cancer related fatigue (CRF) is a stressful and constant tiredness related to cancer and/or its treatment. CRF is the most intense during treatment and can severely interfere with activities of daily living, such as tasks that require physical strength or thinking clearly. Prevalence of CRF has been reported to be as high as 94% during chemotherapy and as high as 34% five years after completion of treatment (Rotonda et al. 2013; Minton & Stone 2008). There is currently no generally-accepted treatment for CRF. However, there is evidence to suggest that light therapy can help with CRF. Non-pharmacological interventions for CRF have also been studied but are costly to implement and involve significant patient burden, particularly among those in active treatment. Given the clinical impact of CRF, the goal of this project is to investigate a novel, low-cost and low-burden intervention for Breast Cancer patients using a particular kind of light treatment called systematic light exposure (sLE) to treat CRF. Two hundred forty-eight breast cancer (BC) patients undergoing adjuvant or neoadjuvant chemotherapy will be recruited from Memorial Sloan Kettering Cancer Center, and City of Hope. The light will be administered by light glasses daily throughout entire duration of chemotherapy. Outcomes will be assessed at eight timepoints during chemo, and a series of follow up assessments at 1 week, 1-month, 3-months and 6-months post-chemotherapy. This study will have major public health relevance as it will determine if an easy-to-deliver, inexpensive, and low patient burden intervention effectively reduces CRF or prevents it from worsening during chemotherapy. Specific Aims: Aim 1: Determine if sLE prevents CRF from worsening in BC patients undergoing chemotherapy Aim 2: Determine whether sLE affects sleep, depression and circadian activity rhythms. Exploratory Aim 3: Investigate sLE normalizes circadian cortisol rhythms. Exploratory Aim 4: Examine whether the effects of sLE on fatigue are moderated/mediated by sleep quality, depression, and/or circadian rhythms.

Inclusion Criteria:

• Newly diagnosed patients with stage 1 through 3a Breast Cancer scheduled to receive a 12-week, 16-week, 18-week, 20-week, or 24-week chemotherapy regimen, adjuvant, neoadjuvant, or already receiving chemotherapy.
• MSH, COH and MSK can recruit participants schedule to go on aromatase inhibitors after treatment.
• Currently over the age of 18.
• English language proficient.
• Able to provide informed consent.

Exclusion Criteria:

• Under age 18
• Breast cancer patients scheduled to undergo chemo regimen other than the 12-week, 18-week, 20-week, or 24-week regimen
• Stage 3B breast cancer inflammatory or Stage 4 breast cancer
• Pregnancy
• Currently employed in night shift work
• Confounding underlying medical illnesses which may cause fatigue (e.g., severe Anemia not controlled by medication, per self-report corroborated by medical chart review (e.g., Hb<10gm/dl))
• Eye Diseases which limit the ability of light to be processed (e.g., untreated cataracts, severe glaucoma, macular degeneration, blindness, pupil dilation problems or retina damage)
• Secondary cancer diagnosis (prior or current) within the past 5 years
• Severe sleep disorders (e.g., Narcolepsy)
• Self- reported history of bipolar disorder or manic episodes (which is a contra-indication for light treatment)
• Severe psychological impairment (e.g., hospitalization for depressive episode in the past 12 months
• Previous use of light therapy to alleviate fatigue or depressive symptoms
• Lives outside of the United States throughout the duration of study

The participant does not know his or her study condition.