Patent ID: 7286215

Claim:
A light measuring apparatus for measuring an illuminance level of light, the apparatus comprising: one or more correction light emitters which illuminate an optical sensor at predetermined illuminance levels, the illuminance levels having known illuminance ratios; a calculation controller configured to calculate correction values at the respective illuminance levels based on expected and actual sensor output levels at the respective illuminance levels; the calculation controller configured to successively turn-on the correction light emitter at the respective illuminance levels, and correct the sensor output level by the corresponding correction value to obtain a measurement output; and a variable gain amplifier configured to amplify the output of the optical sensor in accordance with a plurality of different gains, wherein the calculation controller measures the sensor output levels at the respective illuminance levels in accordance with the plurality of different gains, and calculates the correction value for the sensor output level based on a ratio of measurement results at the respective illuminance levels in accordance with the respective gains.