Some suggestions on the measurement of optical parameters of LED light source

[Source "High-tech LED - Technology and Applications" March issue]

LED light source metering and testing has its own characteristics. It is not appropriate to simply use traditional methods to measure the light color parameters of LED light sources. It is understood that there are large differences in measurement results between local testing organizations. The author believes that there are three main reasons: the first is that the value is not traceable; the second is that the measurement method is not uniform; the third is that the performance of the measuring instrument is not uniform.

Detection is inseparable from reliable measurement standards. Only when the magnitude can be traced back to the superior metering mechanism can the measurement have a reliable basis. At present, traditional standard lamp methods are widely used in China for volume transmission. BDT, BDP type standard lamps are regular standard lamps that comply with the total light quantity standard lamp verification procedures. These lamps are stable in repeatability and are used to store and transmit total luminous flux. At present, due to the discontinuation of standard lamps of BDT and BDP type, there are some alternative halogen lamps and incandescent lamps. These lamps can be used as instruments for measuring the value after aging assessment and selection (although the stability of some lamps) Poor reliability). When the calibration or testing laboratory uses the above-mentioned instruments, it is necessary to confirm the calibration/calibration certificate of these instruments during the calibration period. The certificate is issued by a legal metrological verification agency or testing laboratory and has traceability information, verification procedures or Calibration technical specifications, calibration data, and measurement uncertainty.

In the case that the certificate is legally valid, accurate calibration and use of the instrument with the highest performance measurement can obtain accurate results. Incorrect use of the standard lamp and measuring device will only measure the error value, and the error is often not easily detected. This is the most overlooked problem for manufacturers and inspection organizations, that is, measurement standards and methodological issues.

In the following, the author will discuss the problems that should be paid attention to in measuring the color parameters of the light photometer and the spherical photometer commonly used in China.

The process of measuring the total luminous flux by the distribution photometer is to measure the spatial light intensity distribution curve of the light source and calculate the total luminous flux of the light source by numerical integration. There are two ways to calibrate it. The first is to use a standard light intensity lamp, or a distance calibration from the standard illuminometer and the center of rotation to the detection surface. This method is an absolute measurement. The second is to use a total luminous flux standard lamp. This method is a relative measurement method in which the total luminous flux of the lamp under test is obtained by comparing the readings of the standard lamp and the lamp under test. At this time, the spatial light intensity value is calculated using the relative light intensity distribution curve and the total light flux value. For the measurement of chromaticity parameters, a spectrometer that is calibrated with a distributed temperature standard lamp is used.

For more information, please refer to the March issue of "High-tech LED-Technology and Applications" magazine