Abstract: A light activated acoustic pinger that is useful for underwater three dimional homing. The pinger includes a spherical lens system, a tone burst generator electronics system and a high pressure water tight encasement. When a light source used by an underwater diver, submersible, underwater television system or navigator is panned on the pinger lens system in either the X or Y planes the ping rate will vary depending upon the incident angle of the light received by the spherical lens. In addition, moving the light toward the pinger in the Z direction will increase the ping rate. From the ping rate and the movement of the light source in the X, Y and Z directions an underwater navigator can determine the direction of the pinger and target. There is no battery drain until the pinger is activated by light and therefore targets that have been lost for several years may still be found based on battery shelf life.