An improved sensor (102) for rate monitoring in mobile devices, wearables, security, illumination, photography, and other devices and systems uses an optional phosphor-coated broadband white LED (103) to produce broadband light (114), which is then transmitted along with any ambient light to target (125) such as the ear, face, or wrist of a living subject. Some of the scattered light returning from the target to detector (141) is passed through spectral filter set (155) to produce multiple detector regions, each sensitive to a different waveband wavelength range, and the detected light is analyzed to determine an interval between repetitive events such as heartbeat or respirations, in part based on a noninvasive measure of components of the bloodstream. In one example, variations in oxyhemoglobin of the arterial bloodstream of the subject over time such as hemoglobin and water are determined based on the detected light, and the interval between cycles is then determined based on the in components of the bloodstream over time, with venous compartment changes as a result of body movement and body position changes, and skin surface compartment changes as a result of sensor movement, substantially removed. In the absence of the LED light, ambient light may be sufficient illumination for analysis. The same sensor can provide identifying features of type or status of a tissue target, such as heart rate or heart rate variability, respiratory rate or respiratory rate variability, respiratory depth, or even confirmation that the tissue is alive. Rate monitoring systems incorporating the sensor, as well as methods, are also disclosed.
