A wearable apparatus including a plurality of waveguides each configured to act as a conduit for light emitted from an illumination source to a photodetector via an interaction portion of the respective waveguide, the interaction portion of each waveguide configured to channel the light out of the respective waveguide to enable interaction of the light with the wearer's body and back into the respective waveguide to enable detection of the interacted light by the photodetector.
