Ambient lighting has emerged as a key atmospheric factor influencing how consumers process environmental cues and their behaviors. However, surprisingly little research has examined how people think and feel in the dark (lower than 15 lux). This is particularly relevant given that consumers routinely work, pay bills, relax, consume and make purchases in settings with little or no light. My dissertation addresses this gap by examining how consumers regulate their goals and process information when the light is off, and how that impacts their decision making in three substantive domains: risk-taking behavior, decision quality, and persuasion. In Essay 1, I propose darkness enables risk-taking behavior, and this effect happens through the calmness and relaxation induced in the dark. One caveat is that the decisions have to be made in a familiar setting. The effect was reflected in participants' decisions to invest in riskier yet lucrative stocks, to gamble with the riskier choice, to eat at a foreign restaurant, and to choose a supplement that has potential side effects in a field experiment and three lab experiments (pre-registered). In Essay 2, I propose that when the light is off, consumers are indeed induced to adopt an effortful processing mode. Across four experiments (one field experiment, two lab experiments, and one online experiment), darkness promotes higher quality decisions across consumption contexts (financial, food, and product choices) compared to higher luminous levels. Together, this dissertation explores the intriguing phenomenon of ambient darkness and extends current understandings on ambient lighting and consumer behavior. The essays also offer robust findings through field and lab experiments with tendency and incentive-compatible outcomes.