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Standard lamps defined in lighting optics

All values of light are related to the original standard of light. The original standard is a perfect radiator with a temperature of 2045K, the freezing point of platinum, and a brightness of 60 candlelight/square centimeter. This photometric standard is generally kept by the National Metrology Bureau, and the agency prepares some lamps that have been calibrated with high precision as secondary standards for luminous flux or light intensity in photometric measurement. The accuracy of photometry depends on the type of standard lamp and the accuracy of the calibration bulb. This secondary standard must be used to calibrate a number of working standard lamps, and they must be inspected regularly, so that the secondary standard lamps do not need to be used frequently and their calibration can be maintained for a considerable period of time. Where standard lamps are often used, such as routine photometry, it is best to calibrate a group of lamps according to the working standard lamps, and use this group of lamps to calibrate the photometer on a daily basis. When high-precision measurements are required, two secondary standard lamps should be used, one at the beginning and the other at the end. The results measured by each standard lamp are calculated and the average is taken. The results of the two standard lamps should be quite consistent within the allowable range, otherwise it is necessary to use another sub-standard lamp to test the problematic lamp.