Light detection system and discharge probability calculating method

A discharge probability calculating method of a light detection system comprising:

• a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off;
• a second step of detecting a discharge current of the optical sensor in the first state;
• a third step of detecting a discharge of the optical sensor based on the discharge current in the first state;
• a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage;
• a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is different from that of the first state and a pulse width of the drive pulse voltage is the same as that of the first state;
• a sixth step of detecting a discharge current of the optical sensor in the second state;
• a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state;
• an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage;
• and
• a ninth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and a received light quantity received by the optical sensor is the reference received light quantity, and a difference in received light quantity received by the optical sensor between the first state and the second state, and calculating a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth and eighth steps, and the pulse width of the drive pulse voltage in the first and second states.