The Spectroradiometer Integrating Sphere System, there are two important parts: one is measuring and analysis; another is assistant part which providing testing environmental. Here we will discuss the assistant part, we knew that the integrating sphere spherical aggregates, the inner wall of integrating sphere is coated with a highly reflective coating material to the effect of light refraction. Here to two points: First, according to the lamp size, how choose suitable integrating sphere; Second, according to the types of lamp, how to choose right test method. More details refer below.
First, according to the lamp size, how choose suitable integrating sphere. Normally, the diameter of integrating sphere from several centimeters to several meters. In the lighting industry, the size of integrating sphere from 0.3 meter to 4 meters. The 0.3 meter integrating sphere mainly focus on special test, like laser. There can divide several parts: 0.3M/0.5M mainly test single LED, due to the light source of single LED is very week, it may can’t detective the light source if use big size integrating sphere, the 0.3M or 0.5M is most suitable for this kind of lamp; the second is 1 meter integrating sphere, this integrating sphere suitable for test LED bulb, CFL lamp, spotlight and flashlight; the third is 1.5M to 4M which suitable test all kind of lamps, the 4M or 3M integrating sphere depend on user’s budget and what’s purpose of it. Normally, like the national lab or third party test lab would choose them for LED deeply study and research. In the theory, as long as the size of measured lamp smaller than integrating sphere size are can be tested, but in the practice, if there have big proportion between measured lamp and integrating sphere, the test tolerance is huge. The same, if we use 1M or 1.5M integrating sphere measuring HID lamp(output power more than 500W), the test tolerance is huge too or it can’t be test. On the one hand, the signal of HID lamp is too strong for spectrometer; on the other hand, there will happened self-absorption effect if HID lamp have big output power, the test tolerance will be big if don’t use anxuliary lamp device. For the self-absorption effect, the IES-LM-79 Clause 9.2.5 mentioned it. As we know that the light source is fire in luminous at all direction, the surroundings will absorb part of the light source more or less. When we use integrating sphere measuring total luminous flux, there must be have self-absorption effect if measured lamp have big output power. The CIE standard have mentioned the type of integrating sphere, the standard suggest use 2 meters integrating sphere or bigger size integrating sphere to testing HID lamp. At the same time, we need use anxuliary lamp device to reduce this test tolerance when testing HID lamp, normally, the anxuliary lamp is application with halogen, incandescent or white LED light source.
The second is how to choose test way of integrating sphere according to different type of lamps. Normally, the integrating sphere have two test methods: one is center test(4π test); another is side opening test(2π test). The IES-LM-79 standard have mentioned 4π test method. The 4π test method suitable test SSL product which light source fire all the direction; the side opening 2π test suitable test SSL which light source fire fixed direction, we can learn more details at IES-LM-79 claim 9.2.3. In practice, the LED bulb, CFL, HID and so on are suitable use 4π test method; and LED street lamp and LED panel are suitable use 2π test method.
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