Bright light therapy and the broader realm of chronotherapy remain underappreciated and underutilized, despite their empirical support. Efficacy extends beyond seasonal affective disorder and includes nonseasonal depression and sleep disorders, with emerging evidence for a role in treating attention-deficit/hyperactivity disorder, delirium, and dementia. A practical overview is offered, including key aspects of underlying biology, indications for treatment, parameters of treatment, adverse effects, and transformation of our relationship to light and darkness in contemporary life.