Light detection device and sheet processing apparatus including the same

A sheet processing apparatus comprising:

• a conveyor path which conveys a sheet;
• a first sensor which detects fluorescence from a first detection position on the conveyor path along which the sheet is conveyed;
• a second sensor which detects afterglow from a second detection position on the conveyor path along which the sheet is conveyed;
• a lighting device which applies excitation light over a range including the first detection position and not including the second detection position;
• a first reference plate which emits reference light toward the first sensor, the first reference plate including fluorescent material which emits fluorescence by being excited by the lighting device;
• a second reference plate which emits reference light toward the second sensor when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second sensor;
• and
• a correction controller which corrects a result of detection by the first sensor based on the reference light emitted by the first reference plate and detected by the first sensor and to correct a result of detection by the second sensor based on the reference light emitted by the second reference plate and detected by the second sensor;
• a determination controller which determines whether or not the sheet contains each of fluorescent printed information and phosphorescent printed information, based on a fluorescent image detected by the first sensor and an afterglow image detected by the second sensor;
• and
• a classification processor which determines a type of the sheet based on a result of the determination by the determination portion and classifies the sheet by type.