In optical testing, the measurement of luminous flux and color temperature are essential. There are two test equipment for the measurement: Integrating Sphere Testing System and Goniophotometer. Here we give you a brief introduction to the difference of these two test system:
The Integrating Sphere Test System make measurement using integral method. Firstly, calibrated the system with a standard lighting source and then measure the sample lamp. The test result of luminous flux or color temperature is the relative value of the data of the standard lighting source. The measurement is made through the diffuse reflection spread the light into the optical fiber, and then measure it, the test time is very short, only need several seconds.
In the process of diffuse emission, the light will be affected by the self-absorption performance of the lamp housing, so there may be a certain error in the test results. In addition, if the illumination angle of the lamp is too small, there will be light loss in the integrating sphere due to diffuse reflection, which will result in the light finally transmitted to the spectrometer will be a little different from the original light source, so the test result may would have a certain error. Ans these errors can be reduced in the following ways:
For the error caused by the casing, we can use the auxiliary lamp to correct the test result. The method is as follows: (1) Put the standard lighting source into the integrating sphere and not light it, put the auxiliary lamp into the ball and light it, then test (2) Take out the standard lighting source, put the sample light into the integrating sphere and do not light up, also light up the auxiliary and then test it. (3) By comparing the difference in luminous flux measured in the above two states, the software will form a correction factor (the self-absorption coefficient of the casing). This factor can be used to calculate the test results when testing the sample lamps of the same type of casing.
The error caused by the illuminating angle can be reduced through 2π test method. If the illumination angle is small, the 4π test method will result in uneven illumination in the ball, which will lead to the test error, and the 2π test method can reduce the unevenness of the light source inside the ball. Thereby reducing the test error of the luminous flux.
The goniophotoometer make measurement using photometric method. During the test, During the test, the sample lamp or probe under test can be automatically rotated under the control of software to obtain the parameter values at different angles. The test result is a spatial luminous intensity table and a spatial color table, showing the values of in different directions, not just the average value. The initial test data can be referred to the following data sheet:
And the distributed photometer test is basically not affected by the casing of the lamp, the angle of lamps. And of course, the average value of the luminous flux and color temperature can also be displayed in the test report.
In general, if test the parameters related to space, angle, and distance (such as luminous intensity distribution, UGR, etc.), it needs to be tested with goniophotometer. According to the formal requirements, the integrating sphere system is used to test the lighting source, and the goniophotometer is used to test the luminaires. In addition, you can also confirm the requirements by referring to the following methods:
1. For general quality inspection, use the integrating sphere test system; when it is required to have a higher laboratory, it is recommended to use goniophotometer.
2. Test duration: The integration sphere test system can make the measurement in just a few seconds after the calibration, and the goniophotometer needs at least 15 minutes to make the measurement.
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