The proposed multi-site randomized controlled trial (RCT) will investigate a novel intervention, systematic light exposure (sLE), to treat cancer-related fatigue (CRF) among Multiple Myeloma (MM) and Diffuse Large B-Cell Lymphoma (DLBCL) following autologous stem cell transplantation (ASCT). Cancer related fatigue (CRF) is persistent exhaustion related to cancer and/or its treatment. CRF is the most common cancer side effect and can severely interfere with activities of daily living long after completion of all medical treatment. Pharmacologic agents to treat CRF have been studied but there is insufficient evidence to recommend their use. Non-pharmacological interventions for CRF (including yoga, cognitive behavior therapy, hypnosis, and exercise) have also been studied; however, such interventions are costly to implement and involve significant patient burden. sLE is a low-cost, low- burden intervention that we have found to have beneficial effects for patients post-ASCT. The investigators initial randomized trial for CRF found that certain light exposure was associated with clinically significant reductions in fatigue (effect size d=0.98) More relevant to the proposed research is the preliminary investigation with sLE to treat CRF in MM and DLBCL which found that patients receiving certain sLE reported significantly less fatigue ( p=0.052). The proposed RCT will test the efficacy of sLE on CRF. It will also assess the effect of sLE on sleep, depressive symptoms, and both activity and cortisol circadian rhythms as these related processes have been hypothesized as possible mechanisms of