A method of managing power in a wearable computing device, the wearable computing device having an electronic display with a configurable brightness level setting, a light source, and a light detector, the light source positioned on a wrist-side of the wearable computing device to direct light into tissue of a user when the user is wearing the wearable computing device on a wrist of the user, the light detector positioned on the wrist-side of the wearable computing device adjacent to the light source to detect light from the light source that reflects back from the user, the method comprising:
- placing the wearable computing device on a wrist of a user;
- turning the light source on and off,
- collecting data via the light detector at least while the light source is off to provide information for evaluation relative to an ambient light level;
- and
- modifying the configurable brightness level setting of the electronic display based at least in part on the ambient light level.