It is well known that testing LED luminous flux in CIE121:1966 Clause 6.1, CIE127-2007 Clause 6.2 and IES-LM-79-08 Clause 9.0 have mentioned two test methods: one is to test with an integrating sphere plus spectrometer or spectroradiometer Integral method, this is the relative measure of total luminous flux (CIE121: 1966 Clause 6.1.1, CIE127-2007 Clause 6.2.2 and IES-LM-79-08 Clause 9.0); the other is the photometric method using a distributed photometer This is the absolute measure of total luminous flux. If we use the integral method and the photometric method to test the same lamp, we will find that the total luminous flux data of the two tests are quite different. This article focuses on the differences in lumen testing of LED luminaires in integrating spheres and distributed photometers.
The principle of the integral method for testing total luminous flux is calibrated by the luminous flux standard. Since the standard lamp is used for calibration, it is not necessary to know the spectral output of the sphere. The luminous flux φTEST(λ) of the LED lamp product under test is calculated in comparison with the standard lamp. In general, the integration method is suitable for small integrated LED luminaires and relatively small LED light sources to test the total luminous flux and chromaticity parameters. This is the relative test method for total luminous flux. The integration method has the advantages of fast measurement speed and no darkroom, usually The smaller the volume, the closer the luminaire test results to the point source are.
However, when the larger size LED lamp is tested by the integral method, its limitation is greater than that of the photometric method. The first is to use the integral method to test the luminaire, there will be many forms of LED lights, LED bare light source, spherical LED bulb, LED lamps, etc., and the type of LED luminaire has a great impact on the final luminous flux test. At the same time, the integral method also needs to do the calibration of the integrating sphere. Usually, if you are testing LED luminaires, the standard lamp needs to have similar illuminating characteristics as the lamp under test. It is best to use a stable white LED. Of course, other types of lamps can be used as calibration sources, but this will affect the accuracy of calibration. Sexuality; secondly, the difference caused by the test method: Generally speaking, if the lamp under test is to illuminate around, it is necessary to use 4Ï€ test mode to install the lamp under the center of the integrating sphere (IESLM-79-08 Clause 9.2.5) Such test results are the best, if the luminaire is directional, such as LED panel lights, LED street lights, etc. need to be installed on the side of the integrating sphere to do 2Ï€ test (IESLM-79-08 Clause 9.2.5). For the integrating sphere 4Ï€ test method, if the measured lamp power is large or the lamp housing occupies a large size of the entire lamp, there will be more or less self-absorption effect during the test. In this case, an auxiliary lamp is needed to compensate for this error. (IESLM-79-08 Clause 9.1.5). In general, the integration method is suitable for small integrated LED lamps and relatively small LED light sources. Testing the LED lamps with integral method can ensure the accuracy and stability of the total luminous flux results; for example, when testing large-size LED lamps The limitation of the integral method is relatively large. For the reason mentioned above, the final total luminous flux test has certain uncertainty.
The use of photometric method to test total luminous flux is to use distributed photometric timing, and its total luminous flux test has few limitations. The principle of photometric testing of total luminous flux is that the distributed photometer measures the light intensity of the light source (or the illuminance of the light source at a given distance) in many different directions of the light source, and derives the light intensity data from each direction. Total luminous flux. Compared with the integral method, the photometric method is theoretically free of errors due to the difference in the intensity distribution of the test source. Therefore, it is an absolute test method for the total luminous flux of the LED. It does not require the total luminous flux standard, but it requires a long time for each sample. Measurement time. The use of photometric methods, ie, distributed photometer testing, involves Type C Goniophotometer (IES-LM-79-08 Clause 9.3.1, CIE121: 1996 Clause 3.2), darkroom, test distance (IES-LM-79-08 Clause 9.3, CIE121: 1996 Clause 6.2.1.4) and so on. The difference in the total luminous flux output of the distribution photometer is mainly determined by the type of the distribution photometer, the test method (CIE121: 1996 Clause 3.4.2, Clause 3.4.1 and Clause 3.4.3), the test distance, the photometric probe lamps, etc., according to To test different types of LED products , we can adjust the relevant test methods or equipment; if you encounter LED beam products with narrow beam angle, we can choose a small size distribution photometer, select Type C Goniophotometer, adjust the test distance, select a higher level Class L's photometric probes enable high-accuracy testing of total luminous flux. In the test of the total luminous flux of the LED, the photometric method can achieve the highest precision measurement. Due to some limitations inherent in the integration method, it is difficult to eliminate the error by adjusting the device, and only to minimize this error; and the photometric test The required equipment itself is not too limited, so the error can be compensated by the modulation and operation of the equipment.
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