Cognitive ability varies across the lifespan, with optimal functioning in healthy adults. Stable neural circuit functioning in the hippocampus, the brain area responsible for memory encoding and cognition, is essential to maintenance of an individual’s ability to meet changing environmental demands. Conditions of physiological desynchrony, such as circadian disruption, can negatively and permanently impact cognition, even when experienced during adulthood, a time of minimal circuit restructuring. Circadian-rhythm-associated disorders present neurocognitive changes dependent on cause and age of disease onset. The present series of studies explored the extent to which timing and type of light exposure can instigate circuit dysfunction or treat circadian rhythm-associated neurodegeneration. This dissertation sought to elucidate the underpinnings of light-mediated cognitive health during the time windows leading into and out of adulthood, two time points vulnerable to cognitive dysfunction. In the first study, the impact of chronic jet lag on adolescent and adult hippocampal and prefrontal cortex neurocircuitry, and associated cognitive behaviors, was examined. In the second study, the efficacy of an imperceptible gamma-wave flickering light on cognitive decline in a mouse model of Alzheimer’s disease, a disease comorbid with disrupted sleep-wake cycles, was explored. In the third study, the specific neuroimmune-mediated mechanisms accounting for the neuroprotective ability of gamma-wave lighting were examined. These experiments shed light on the connection between circadian and cognitive circuit functioning throughout an organism’s life, and provide a novel perspective on light as a mediator of physiological dysfunction in vulnerable developmental windows, and a source of neuroprotection in the face of neurodegeneration.