Patent ID: 8046188

Claim:
A temperature sensor for measuring temperature in accordance with the time-of-life of a fluorescent light that is produced by a phosphor, comprising: a light source emitting an excitation light; a phosphor producing a fluorescent light through the excitation light; a photodetector device detecting the fluorescent light and outputting a fluorescent light signal in accordance with the intensity of the fluorescent light; and a processing portion calculating the temperature based on the fluorescent light signal from the photodetector device, wherein: the processing portion is configured to: calculates an integral value for the fluorescent light signal in each of at least three time periods set in advance during the decay of the fluorescent light signal; calculates a first difference value from the integral values for a first and a second time period having a first time duration; calculate a second difference value from the integral values for a third and a fourth time period having a second time duration; calculates, from a ratio of the first and second difference values, a variable that varies depending on the measurement temperature; and references a relationship between the temperature and the ratio of difference values, stored in advance, to convert the calculated variable into a temperature.