Abstract: A biofeedback device and the light sensor used thereby are described herein that can be mounted on or integrated with eyewear such as swimming goggles. The biofeedback device may include a heart rate measurement apparatus comprising a reflected green light sensor, and first, second, and third green light emission elements. The biofeedback device may include a housing having a first portion and a second portion, which each of the first and second portions having a first side and a second side. At least a portion of the heart rate measurement apparatus may be disposed within the housing first portion and may be exposed through an opening in the second side of the housing first portion. The biofeedback device may also include an opening that allows the device to be removably engageable with at least a portion of the swimming goggles.