Light exposure from at least one light source is received with a light detector of a light monitor that includes at least one of (a) an output device and (b) a communication device transported by a user. The light detector converts the light exposure into an electrical signal, and the current time of day at which the light exposure is received is recorded. An instantaneous light exposure value is generated from the electrical signal, and a weighting function is applied to the instantaneous light exposure value as a function of the recorded time of day associated with the light exposure to produce a weighted instantaneous light exposure value. The weighted instantaneous light exposure value is integrated to produce a weighted cumulative luminous exposure value; and the weighted cumulative luminous exposure value is compared with an established luminous-exposure target.