Text / Cai Yi (Hangzhou Quality and Technical Supervision and Inspection Institute)
Semiconductor lighting has been supported by the national â€œEleventh Five-Year Planâ€. New words such as green lighting and energy-saving lighting have been seen everywhere. In the semiconductor lighting industry, high-power LEDs should be in an absolute guiding position. At present, the manufacturers of high-power LED packages in China are flourishing and blooming everywhere. But in fact, most LED application manufacturers still use imported or Taiwan or a few well-known enterprises in China, and generally lack trust in domestic high-power LEDs. Especially in the LED heat dissipation process, luminosity attenuation, chromaticity change, light color consistency and so on. This article will focus on how to find out the quality hazards of LEDs through effective testing methods, and how to perform fast and effective spectral separation of LEDs for light color control.
Second, the aging test
Everyone knows that LEDs, especially high-power LEDs, will have a certain attenuation in the initial lighting stage. In order to provide stable products or application manufacturers, the packaging companies usually do some sophisticated tests in order to obtain stable LED source materials. Of course, LED sophisticated testing can be done in a variety of ways, such as routine aging, overcurrent shock destructive testing, and the like.
1. Multiple tubes are aging in series (Figure 1, Figure 2)
1) Constant voltage aging circuit 2) Constant current aging circuit
2. Multiple tubes are aging in parallel (Figure 3)
3. Multiple tubes are connected in series and aging (Figure 4, Figure 5)
4. Single tube constant current aging (Figure 6)
Compare the above four aging methods: 1. As long as one LED has a quality fault, such as LED short circuit or open circuit will affect the working current parameters of other LEDs. The second method is better than 1, 3 kinds. Any change in LED characteristics will not affect other LED aging parameters, but in fact, the method of resistor current limiting is unreliable, the resistance of the resistor itself drifts and the voltage of the LED itself. Changes in characteristics can seriously affect the LED parameters. Obviously, the fourth single-tube constant current aging captures the LED current operating characteristics and is the most scientific LED aging method. Aging should be a very important process in the test process, but in many enterprises, it is often neglected and cannot be properly and effectively aged. The analysis of all parameters including brightness, wavelength, etc. performed by the LED itself will be uncertain. .
Over-current impact aging is also an aging method often used by manufacturers. It is usually used for constant temperature sources with adjustable frequency, adjustable current and adjustable duty cycle. It is expected to judge the quality and expectations of LEDs in a short time. life.
Third, light failure test
The luminosity attenuation of high-power LEDs (including luminous flux attenuation, color change, etc.) is an important criterion for measuring LED quality. It is a problem that many LED manufacturers and LED users are extremely concerned about. Therefore, the LED photometric attenuation test appears in the LED quality test. It is very important.
At present, there are three methods generally tested by manufacturers: 1. Visual inspection, that is, continuously lighting the LED, and observing the change of brightness and color with eyes. 2. Light color test instrument analysis, that is, in the process of continuously lighting the LED, continuously remove the LED into the light color test instrument for testing, record the test result, and finally draw the test result report through tools such as EXCEL. 3. Using professional light decay test instrument measurement, the LED is placed in the test system to illuminate continuously, the system tracks and monitors LED brightness and color change in real time, and automatically generates data report, which provides more objective and more objective for LED light attenuation analysis. For scientific data.
Fourth, effective spectroscopic color separation
In recent years, LED application products, especially semiconductor lighting products, are increasingly demanding for high-power LEDs, and at the same time, the quality requirements for LEDs are getting higher and higher, which are mainly manifested in the following aspects:
1. Forward voltage test:
The range of forward voltage needs to be within the permissible range of circuit design. Many customers design to drive the LED to illuminate in a voltage mode. The forward voltage will directly affect the change of the overall parameters of the circuit, which will bring product quality. Hidden dangers. In addition, for some products that require power consumption of the circuit, it is desirable to ensure that the forward voltage is as low as possible under the same luminous efficiency.
2. Reverse leakage current test:
The reverse leakage current is lower than the required value when loading a certain voltage. In the production process, the LED reverse leakage current is too high due to static electricity, chip quality and other factors, which will cause great hidden dangers for LED application products. After a period of use, it is easy to cause LED dead lights.
3. Luminous flux binning:
The luminous flux value is an indicator that LED users are very concerned about. LED application customers must know the range of LED luminous flux they use to ensure the uniformity and consistency of their brightness.
4. Main wavelength binning:
For monochromatic LEDs, the dominant wavelength is an important indicator for measuring its color parameters. The dominant wavelength directly reflects the human eye's visual perception of LED light.
5. The chromaticity coordinates x, y are:
For white light or monochromatic light, the color parameter can be used to express the color region of the LED. Generally, four points x, y are required to determine a chromaticity area. It is necessary to ensure that the LED is at the required four points by certain testing means. Within the x,y chromaticity area.
6. Relative color temperature binning:
For white LED color temperature is a parameter used in the color industry to characterize it, this parameter can directly characterize whether the LED color is warmer or colder or more white.
7. Color rendering index binning:
The color rendering index is directly related to the degree of discoloration of light on the object, which is very important for LED lighting products. At present, many domestic manufacturers carry out automatic binning through a professional high-power LED splitting and separating machine.
With the continuous advancement of technology, new light sources continue to emerge, providing very favorable conditions for architectural lighting design. High-power LEDs as a new type of lighting technology, with low operating voltage, low power consumption, high luminous efficiency A series of advantages such as extremely short response time, pure light color, firm structure, impact resistance, vibration resistance, small size and low cost have begun to be accepted by many people. However, it is undeniable that at present, due to the development of the domestic high-power LED industry, it is still in the stage of performance improvement and the initial stage of limited application. Its optical characteristics have problems such as uneven color of light, and it has its luminous efficiency, color temperature and color rendering index. limitation. Therefore, we must ensure the smooth development of technology research and development and improve the quality of our products through perfect testing methods. We also hope that our country can develop a standard system for semiconductor lighting as soon as possible, so as to effectively regulate the semiconductor lighting market.
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