to the present invention referring to fig3 the driving circuit according to the present invention includes a light emitter 1 a power supply 2 for supplying a power to the light emitter 1 a controller 3 for controlling the power supply 2 and the number of used bits of respective color components and a detective sensor 4 for sensing a grade of an external light the light emitter 1 emits lights of the three primary colors for instance an organic el has a structure wherein organic compounds that emit respective lights of red green and blue are formed on a thin glass substrate and a protective layer is formed on the organic compounds especially the light emitter 1 according to the present invention uses the different numbers of bits and luminance in the outdoor or indoor with respect to the respective colors the light emitter 1 has electrodes provided on luminous materials for emitting the respective colors the power supply 2 supplies the power to the respective luminous materials especially the power supply 2 applies a constant voltage to the respective electrodes at this time the controller 3 controls the power supply 2 to keep a constant output voltage and controls the numbers of used bits of the respective color components that is the controller 3 adjusts the numbers of used bits of the respective color components of the light emitter 1 with reference to information sensed by the.