Abstract: a light-monitoring apparatus includes a power source, a light detector, a computer processor coupled with the power source and in communication with the light detector and configured to receive and record light exposure detected by the light detector, an output device coupled with the computer processor, and a computer-readable medium coupled with the computer processor and storing instruction code for summing the recorded light exposure from the computer processor over time and communicating a signal to the output device to generate and communicate a signal indicating that a cumulative threshold light exposure for achieving a health benefit has been reached. The apparatus can accordingly be used by an individual to monitor cumulative light exposure from both natural and artificial sources, e.g., in the treatment of seasonal or non-seasonal depression.