How to Use an Integrating Sphere for LED Testing

A integrating sphere is an enclosed hollow sphere lined with a white diffusing material. There is one or several openings on the sphere wall used as an entrance opening and a receiving opening for a receiving element. The inner wall of the integrating sphere should be well spherical and usually requires that its deviation from an ideal sphere should not exceed 0.2% of its inside diameter. An ideal diffusing material, i.e. a material with a diffusion coefficient close to 1, is coated on the inner wall. Magnesium oxide or barium sulfate are commonly used materials and are sprayed evenly after mixing with a glue.

The spectral reflectance of the magnesium oxide coating is above 99% in the visible spectrum. In this way, the light entering the integrating sphere is repeatedly reflected on the inner surface to form an even illumination on the inner wall. In order to achieve higher measurement accuracy, the opening ratio of the integrating sphere should be as small as possible. The opening ratio is defined as the ratio of the spherical area at the opening of the integrating sphere to the entire surface area of the inner wall.

The basic working principle of Integrating Sphere:
Light enters through the input port and then is uniformly reflected and scattered inside the sphere, so the light obtained from the output port is a quite uniform diffuse beam. The incident angle, spatial distribution and polarization of the incident light will not affect the intensity and uniformity of the output beam. Also, the output light has gone through integration within the integrating sphere, so it can also be used as a light intensity attenuator. The ratio between the output strength and the input strength is approximately the area of the output port/the surface area of the inside of the integrating sphere.

As light source technology advances, LED bulbs are increasingly favoured by the public due to their higher energy efficiency and lower operational costs than traditional bulbs. However, LED bulbs also face technical challenges in extending their service life. Therefore, it is particularly important to conduct efficient tests and verification for the quality and service life of LED bulbs.

Though the technology of LED bulbs has developed rapidly, the test and verification methods have not changed much, which makes it difficult for us to effectively identify and compare the quality differences between different bulbs, as well as properly evaluate the service life parameters that they are advertising.

In this case, it is particularly important to use photosphere method for LED testing. Photosphere method is used to measure the brightness distribution in global illumination tolerance and help researchers and developers of Swiss LED lighting to optimize the design and quality of the bulbs. First, in order to test LED bulbs, we will cast lights onto a photosphere and then use a probe to measure the light distribution, and transfer the data to a computer in order to obtain parameters such as color temperature, brightness, spectrum, etc. Secondly, we use light attenuation to simulate the future impairment of the bulbs, usually adopting certain power attenuation or colour change degree to keep the power and color temperature as close as possible to the actual usage. Finally, by testing samples of bulbs with different manufacturing time, parameter settings and usage, researchers usually draw conclusions to help improve the design of bulbs, optimize its quality and other parameters.

Therefore, the photosphere method is an effective way to conduct comprehensive tests and verification of LED bulbs. It helps researchers to adjust and optimize the design of bulbs in a timely manner, and also effectively control the parameters and service life to meet customer needs, develop high-quality LED bulbs. Compared with traditional testing methods, photosphere method has higher accuracy and efficiency, as well as environmental friendliness. In terms of convenience, economy and quality, it can meet the customer’s requirements, ensure the production of high-quality bulbs and promote the development of the LED industry.

In LED bulb testing, photosphere method is a commonly used technique for testing LED bulb luminous traits. It can detect the illumination directionality of LED bulbs and can deeply judge the lighting performance of LED bulbs by inspecting the dispersion of the light emitted from the bulb.

Compared to traditional luxmeters or probes, photosphere method greatly reduces the testing time and can accurately measure the lighting performance of LED bulbs. So, how to complete photosphere testing for LED bulbs?

Firstly, the tester needs to prepare a three-centimetre-diameter photosphere specifically designed for testing LED bulbs. Secondly, due to the difference in structure between LED bulbs and conventional bulbs, LED bulbs cannot be placed directly on photosphere, so the tester needs to build a special bracket. Then, the LED bulbs are installed on the bracket and the photosphere is placed in the middle of the direction of emission of the LED bulbs in order to ensure the accuracy of the test results. Finally, the tester needs to measure the LED bulbs placed indoors, the angle and illuminance of the measured results can be recorded. If an outdoor measure environment is needed, the tester can use a special radiometer to detect the light dispersion conditions of the LED bulbs emitted.

By the above testing method, we can get accurate and reliable results for LED bulbs’ lighting performance, so as to help us evaluate different types of LED bulbs. With these types of results, technical personnel have sufficient time to study the factors that cause abnormal lighting to enable further improvement of LED bulbs’ performance.

In general, LED bulb photosphere testing can help us understand LED bulb lighting performance more accurately, so that more accurate evaluations can be made for different types of LED bulbs, and LED bulbs’ lighting quality can be better mastered, in order to reduce the rate of abnormal alarms occurred in actual use of LED bulbs.

Now LED lights have become the alternative of home, factory and shopping mall lighting, and the product quality is also one of the main criteria for judging whether it has sustainable lighting, and it is precisely the LED lamp luminaire test that can help us accurately evaluate and test the luminous performance of LED lights, thereby helping us to choose LED lights with better performance, helping us use LED lights more efficiently and thus save our brightness cost.

LPCE-2 Integrating Sphere Spectroradiometer LED Testing System is for single LEDs and LED lighting products light measurement. LED’s quality should be tested by checking its photometric, colorimetric and electrical parameters. According to CIE 177, CIE84,  CIE-13.3, IES LM-79-19, Optical-Engineering-49-3-033602, COMMISSION DELEGATED REGULATION (EU) 2019/2015, IESNA LM-63-2, IES-LM-80 and ANSI-C78.377, it recommends to using an array spectroradiometer with an integrating sphere to test SSL products. The LPCE-2 system is applied with LMS-9000C High Precision CCD Spectroradiometer or LMS-9500C Scientific Grade CCD Spectroradiometer, and a-molding integrating sphere with holder base. This sphere is more round and the test result is more accruate than the traditional integrating sphere.

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

Our main products are Goniophotometer, Integrating Sphere, Spectroradiometer, Surge Generator, ESD Simulator Guns, EMI Receiver, EMC Test Equipment, Electrical Safety Tester, Environmental Chamber, Temperature Chamber, Climate Chamber, Thermal Chamber, Salt Spray Test, Dust Test Chamber, Waterproof Test, RoHS Test (EDXRF), Glow Wire Test and Needle Flame Test.

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Tags：LPCE-2 (LMS-9000)