A wearable device includes a measurement device having light emitting diodes (LEDs) measuring a physiological parameter. The measurement device modulates the LEDs to generate an optical beam having a near-infrared wavelength between 700-2500 nanometers. Lenses receive and deliver the optical beam to tissue, which reflects the optical beam to a receiver having spatially separated detectors coupled to analog-to-digital converters configured to generate receiver outputs. The receiver captures light while the LEDs are off, and reflected light from the tissue while the LEDs are on, to generate first and second signals, respectively. Signal-to-noise ratio is improved by differencing the first and second signals and by differencing the receiver outputs. The measurement device further improves signal-to-noise ratio of the reflected optical beam by increasing light intensity of the LEDs relative to an initial light intensity. The measurement device generates an output signal representing a non-invasive measurement on blood contained within the tissue.