A damper assembly has a longitudinal axis and includes a damper housing with a side wall portion and an end wall portion defining a damping chamber containing a quantity of damping fluid. A photon source and a photon receptor are operatively disposed in optical communication with the non-gaseous damping fluid in the damping chamber. The photon source is operable to direct a photon through the non-gaseous damping fluid toward an associated target surface. The photon receptor is operable to receive the photon reflected off the associated target surface through the non-gaseous damping fluid. A sensor suitable for such use as well as spring and damper assemblies and suspension systems are also included.