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LED test technology and equipment development research

Standard and test technology is an important lever to lead the development of LED semiconductor lighting industry. In recent years, with the development of LED industry, LED from device, module to lighting and display etc application product’s standards have a faster development. The international relative standardization organization has released some standards. China is also from tracking to participating and leading the international standards actively, especially the photobiological safety measurement international standard for lamps and lamps system.


International organization for standardization IEC is a class A technical advisory body in United States, IEC standards is the most important trade technical document for WTO. China gets the international recognition in lighting optical detection technology and starts to lead IEC optical measurement standards, which will promote China’s semiconductor lighting LED detection equipment development.


In the LED detection technology, because LED products and traditional light source have big characteristics difference. LED luminescence has a close relationship with LED junction temperature, in the optical and photoelectric parameters test for LED products, the change of environmental temperature, the radiator or body temperature all can change the junction temperature of LED, thus affect the light output. In the LED photometry test, light emitting devices and lamps shell often can not be separated; they need one test, usually we adopts absolute photometry measurement method. Some high brightness LED blue light can cause eye retinal photochemical damage. According to IEC62471 Photobiological Safety of Lamps and Lamp System series standards, the photochemical damage test for LED products is one of the industry concerns currently. In addition, LED products has long life characteristics, we can not make it like ordinary lighting products for long burning point test, we must adopt the accelerated test method to predict the effective life of LED products, such as American “Energy Star” adopts LM-80 standard, China is working out the LED life accelerated test method standard.


Therefore, LED products performance measurement technology and test equipment has fast development in international in recent years. In China, with the fast development of LED industry, test technology and innovation capacity of equipment have significantly increased, China launched a series of advanced test equipment to meet the urgent need of current industry; especially in the LED product photometry and energy efficiency test, luminaries space light distribution measurement, life accelerated test, optical radiation safety test etc, China develops advanced test equipment with international competitiveness.


1. LED product photometry and energy efficiency test

In the performance test for LED product, temperature control is very important. According to the relative standards at home and abroad, LED devices generally control junction temperature or shell hot spot temperature; for LED module, it controls the hot spot temperature for the heat sink on modules. However, LED application products are based on ambient temperature. Therefore, in photometry and energy efficiency test for LED products, aimed at LED devices, modules and application products, the temperature control method is very important for test equipment.

The beam directivity of some LED products is very strong, in integrating sphere measurement, beam projection area and screen position is very sensitive. According to IESNA LM79 standard and CIE 127 technical report, it recommends to adopt high spectral reflectance sphere inner coating material. USA NIST promotes the international LED standard test method standard, walking in the forefront of the world; it also puts forward high requirements to the test equipment.


2. LED lamp and luminaries space light distribution test

Goniophotometer is the photometry measurement device to measure light source and luminaries space light intensity distribution. Picture 2- It is the principle structure of rotating mirror Goniophotometer recommended in CIE 70 technical report, rotating mirror keeps rotate around the central axis. It can set a series of elimination of stray light aperture accurately between rotating mirror and photometric detector; it can eliminate stray light very effectively. This Goniophotometer is suitable for the space light distribution measurement for all kinds complex beam; it is adopted by more than a hundred of labs in the world, the amount is the first now. Several national laboratory in China also uses this Rotating Mirror Goniophotometer.


In recent years, with the development of LED technology, more and more domestic and international pay attention to the space light distribution measurement for LED products. Compared with traditional light source and luminaries, LED light products often have complex beam distribution and may have a certain space color difference, therefore, it put forward new requirements for LED products spatial light distribution measurement, it not only measures LED spatial light intensity distribution, it also need to measure the spatial non-uniformity of chromaticity. In addition, for many laboratories, space restricts the application of high performance equipment.


3. LED products Photobiological Radiation Safety Test and Assessment

With the development of Photobiological research, people pay more and more attention to light radiation safety problems. Especially, the fast development of LED in recently, the power of chip and external quantum efficiency is greatly improved; high power blue light LED chips are widely applied in the general lighting field; with the development of high power multi-chips integration and second optical technology, it make LED light radiation  harmfulness more attention. Eye retina light radiation safety assessment needs to measure the radiation brightness of 300nm~700nm blue light photochemical damage and 380nm~1400nm retinal thermal hazard.


4. LED Life Accelerated Test


LED products life can be ten of thousands hours, how to assess the product life, the LED industry all pay attention in the world. Feasible method is based on the accelerated thermal test of LED junction work temperature. USA LM-80 standard provides three kinds of test temperature: 85℃, 55℃ and custom(25℃) , to get LED light decay curve under these temperatures, test time is 6000 hours. China is drafting LED life accelerated test method without the detail requirement for the test temperature; generally choose the accelerated test thermal load according to LED structure material characteristics.

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