A curvature or bending and displacement sensor is composed of a fiber optic or light wave guide, for attachment to a member or members being curved or displaced. Light is injected at one end and detected at the other end. Curvature of the fiber results in light loss through an emission surface or surfaces, sometimes in conjunction with a superimposed curvature in a plane other than that of the curvature to be measured, this loss being detected. The loss of light detection is used to produce indication of curvature or displacement. The light emission surfaces extend in various forms, such as a surface strip or band. Particularly, in an example, the emission surfaces extend in a substantially peripheral direction, or in a substantially curved axial direction when in a curved portion of a curved guide. The placement, shape and configuration of the emission surfaces allows adjustment of the linear range of measurement, the overall throughput of light, and the length over which curvature is measured. Two or more light guides can be oriented to given indication of direction of curvature or displacement.