Patent ID: 8797522

Claim:
A light quantity detection device, comprising: a light detector which detects light; an amplifier which amplifies a detection signal from the light detector; an A/D converter which A/D converts the detection signal amplified by the amplifier; a threshold value processing circuit unit which carries out threshold processing to the detection signal A/D converted by the A/D converter by substituting a signal at a level which is equal to or less than a threshold value among the A/D converted detection signals into a preset reference value; and a number-of-photons calculation circuit unit which calculates the intensity of light or the number of photons incident on the light detector from the detection signal which is threshold processed by the threshold value processing circuit unit, wherein the number-of-photons calculation circuit unit calculates the intensity of light or the number of photons incident on the light detector based on a dimension of a signal waveform of the detection signal threshold processed by the threshold value processing circuit unit.