Ray has a built-in solar cell that charges using outdoor sunlight only.
What kind of light works best?
Use direct sunlight outdoors. About one minute per day can sustain operation. Weather, shade, clothing, orientation and usage affect the energy balance. Indoor lighting does not charge Ray.
What if I don't get any light at all?
Ray can last up to about 2 months on battery when sampling about every 5 minutes. Battery life is shorter if the app or firmware samples more often, if step counting is enabled, or if Ray is spending extra energy reconnecting over Bluetooth.
Do I ever need to plug it in?
No. There's no charging port on the Ray. It's completely self-sustaining.