Methods and apparatus to detect an operating state of a display are disclosed. An example device to detect an operating state of a display includes an optical fiber, an optical-to-electrical converter, and a logic circuit. The optical fiber is optically coupled to a light source of the display. The light energy source is configured to emit light. The optical-to-electrical converter is coupled to the light source via the optical fiber and configured to convert light from the light source into an electrical signal. The logic circuit is coupled to the optical-to-electrical converter and configured to generate an output signal indicative of the operating state of the display based on the electrical signal.