Abstract: A sheet type discrimination device includes: a first light source unit that irradiates a sheet with light having a first wavelength and light having a second wavelength; a detection unit that detects light from the sheet and acquires a detection value based on the light; and a control unit that derives a determination result of a type of the sheet, wherein the first light source unit and the detection unit are located on a same side with respect to the sheet, the detection value includes: a first detection value; and a second detection value, and the control unit discriminates first-type recycled paper by first processing using the first detection value, and discriminates second-type recycled paper different from the first-type recycled paper by second processing using the second detection value.

Abstract: A recording medium determination device includes a light emitter, a light detector, and a hardware processor. The light emitter emits inspection light to a recording medium. The light detector detects incident light including at least one of diffuse reflected light of the inspection light emitted to the recording medium and fluorescent light excited by the inspection light in the recording medium. The hardware processor makes a determination depending on a property of the recording medium based on a detection result of first incident light of the incident light in accordance with first inspection light of the inspection light and second incident light of the incident light in accordance with second inspection light of the inspection light obtained by the light detector. The second inspection light has an intensity whose peak wavelength is shorter than the peak wavelength of the first inspection light.

Abstract: A technology aimed at improvement of paper discriminating accuracy is provided. In an image forming apparatus, a control unit derives a discriminating result for types of paper. To be specific, the control unit derives the discriminating result for types of paper using a first detection value based on absorption by the paper of the light having the first wavelength and a second detection value based on absorption by the paper of the light having the second wavelength. The first wavelength ranges from 750 nm to 1100 nm.

Abstract: A recording medium determination device includes a light emitter, a light detector, and a hardware processor. The light emitter emits inspection light to a recording medium. The light detector detects incident light including at least one of diffuse reflected light of the inspection light emitted to the recording medium and fluorescent light excited by the inspection light in the recording medium. The hardware processor makes a determination depending on a property of the recording medium based on a detection result of first incident light of the incident light in accordance with first inspection light of the inspection light and second incident light of the incident light in accordance with second inspection light of the inspection light obtained by the light detector. The second inspection light has an intensity whose peak wavelength is shorter than the peak wavelength of the first inspection light.