||Light is an important entraining agent for endogenous circadian rhythms. Artificial light at night (ALAN) negatively influences the circadian system, inducing acute effects on sleep and cognition, as well as chronic endocrine-disrupting effects resulting in obesity, cardiovascular disease, diabetes, and cancer. Although shift workers may be exposed to extreme ALAN, its impact on their health is obscured by factors such as daylight exposure, meal and sleep scheduling, and physical and social behavior. Studies have revealed a significant increase in breast cancer in high ALAN-polluted areas, although the correlation with outdoor or indoor lighting conditions is controversial. Increasing use of electronic devices makes it difficult to assess ALAN exposure in the general population. The development of surrogate markers and critical parameters is crucial for health study by ALAN exposure, and such markers should include risk factors related to ALAN exposure. The present review considers articles investigating the risk of ALAN for shift workers, the general population, and users of electronic devices, and addresses susceptibility factors, including age, sex, and chronotype. Shift workers may be regarded as an extreme ALAN-exposure group, but the growing use of electronic devices and lifestyle changes in the general population make difficult to differentiate ALAN risks to health.