Patent ID: 8521047

Claim:
An image forming apparatus comprising: a toner carrier comprising a substrate and a transparent film on a surface of the substrate; a toner image forming unit configured to form a toner image onto the toner carrier; and at least one toner concentration sensor configured to sense a concentration of toner carried on the toner carrier, the toner concentration sensor comprising: a first light emitting element and a second light emitting element different from the first light emitting element, the first light emitting element and the second light emitting element each being configured to radiate light directly or indirectly to the toner carrier; and at least one light receiving element configured to receive reflecting light originating from at least one of the first light emitting element and the second light emitting element, a reflection intensity of the reflecting light originating from the at least one of the first light emitting element and the second light emitting element and received by the at least one light receiving element being used to sense the concentration of the toner, wherein the first light emitting element is configured to radiate light having a wavelength that causes equal to or higher than a predetermined reflectance that is sensed by the at least one light receiving element when the light is radiated directly to the toner carrier, and wherein the second light emitting element is configured to radiate light having a wavelength that is different from the wavelength of the light radiated from the first light emitting element and that causes a lower reflectance resulting when the light is radiated directly to the toner carrier than a reflectance resulting when the light is radiated to the toner.