A planar light source of this invention is formed with chamfered portions at an upper end of the light receiving side surface where the light receiving side surface and the light emitting surface of the light guide plate intersect and at a lower end of the light receiving side surface where the light receiving side surface and the reflection surface of the light guide plate intersect. A semiconductive polymer capable of luminescence in an optical device is provided. In the omni-directional scan mode, symbol character data is communicated to the host device irrespective of the activation signal. According to one method, data signals are transmitted over the first data link and the transmitted data signals are captured. The developed imageable elements are useful as lithographic printing plates.