1. The effect where certain transparent dielectrics become doubly refracting when placed in an electric field.
2. The change in the index of refraction of a material when subjected to an electric field.

The effect can b used to modulate a light beam in a material since many properties; such as, light-conduction velocities, reflection, and transmission coefficients at interfaces, acceptance angles, critical angles, and transmission modes, are dependent on the refractive indexes of the media in which the light travels.

The effect wherein certain transparent dielectrics (materials which are poor conductors of electric current) become doubly refracting (bending of electromagnetic waves as they pass between materials with different refractive indices or magnitude of some physical effect) when placed in an electric field.