A method includes emitting optical energy, detecting a feature, emitting optical energy, and determining a physiological parameter. The method includes emitting optical energy having spectral content in a first range. The first range includes green light or infrared light. The optical energy is directed at tissue using a wearable module. The method includes detecting a feature in a photoplethysmogram signal. The feature has spectral content corresponding to optical energy in the first range. In response to detecting the feature, the method includes emitting optical energy having spectral content in a second range. The second range is different from the first range. The method includes determining a physiological parameter using the optical energy in the second range.
