Osram is testing its LED products at its own environmental simulation laboratory in Baden-Wuerttemberg. Influences, such as temperature deviations, humidity or sunlight are being tested.
Since LEDs have become established in almost every sector, quality, in particular, is an important criterion as well as the price. For example, every year Osram, the lighting specialist, carries out over 1,000 tests on more than 100 test systems in a 1,000 m² environmental simulation laboratory in Herbrechtingen (Baden-Wuerttemberg). The different environmental influences are the focus of the tests. The reason for the complex tests is simple: LEDs are often exposed to extreme environmental conditions.
One LED consists of various plastics and metals with differing thermal expansion coefficients. Fast changes in temperature, which occur for example when using a car wash on a sunny day, can lead to damage and stress cracks. In order to test these effects, the test laboratory must perform special temperature shock tests. In doing so, the test samples are placed in a temperature shock test chamber and are alternately exposed to extreme heat and cold in a short space of time.
For example, a usual test would run 1,000 cycles, each consisting of 30 minutes at 125 °C and 30 minutes at a temperature of -40 °C. In the test chamber there is a very homogeneous temperature distribution.
Simulating air humidity in an accelerated manner
Especially in the Asian region, headlamps on vehicles are exposed to strong heat and high air humidity. In order to simulate these environmental influences on headlamps in a realistic manner, the LEDs are tested in special temperature humidity test chambers. In these chambers, they are e.g. exposed for 500 or 1,000 hours to a relative humidity of 85 percent and a temperature of 85°C, which is the equivalent of the climatic conditions in the engine compartment. The test quickly provides reliable information, in particular regarding the corrosion resistance of the test samples.
Separate vibration tests for headlamps and LEDs
Headlamps and LEDs are exposed to constant vibration due to the movement of the engine and the vehicle. In cases, where separate vibration tests had previously been performed, combined vibration and temperature tests are being used today. The tests are carried out in special temperature vibration furnaces. In general, they give more precise results on the real operating conditions. This is confirmed by laboratory head, Dr Sascha Zelt, “In order to simulate this load, we use special thermal chambers from Weiss Umwelttechnik that we fit with a vibration module. In this way, we can precisely detect possible weak points in the LEDs and deduce important information for development and production.”
It is, however, not just temperature deviations and vibrations that affect LEDs. Saline conditions, as occur on roads gritted in winter, also attack the LEDs. In order to simulate these specific conditions, reproducible, accelerated salt spray tests are called upon. For this purpose, the test samples are placed in the climate alternating test unit with a salt spray function and are sprayed for a period between 96 and 240 hours with a five percent saline solution that has a pH value of 6.5 to 7.2 and a water temperature of 35 °C. Afterwards, the LED products are inspected for possible corrosion damage, which can occur in particular in the zone between the metal and plastic components.
Product tests with international standards
The environmental simulation laboratory, which opened in 2011, is accredited by the German Accreditation Body (DAkkS) in accordance with DIN EN ISO/IEC 17025. This standard guarantees that the globally applicable quality standards for the test methods have been observed. Alongside the aforementioned test systems, Weiss Umwelttechnik equipped the laboratory with more than 70 climate test chambers, a sun simulation chamber, a test chamber for pollutants as well as a special dust test device for IP protection tests. Furthermore, the laboratory also conducts mechanical tests, shock and tumble tests as well as vibration measurements.
Proven standard devices for long-term partnership
Weiss Technik systems are tried-and-tested standard models that can be equipped with special options – energizing specimen under precisely controlled climatic environments to simulate real operating conditions is just one of them. Maximal reliability and accuracy are essential when choosing the right equipment. The high variety of different test equipment available caused the need for a simple, uniform and clear operation. The laboratory also offers mechanical tests, impact and falling tests as well as vibration measurements. They offer a high reproducibility and precise test results. That is important for a long life of the LED.
Sammr Nasrallah-Goldberg, Global Head of SP AM-AFTM ATS & QM Services, explains, “For us, customer service is a top priority. We also demand this from our suppliers. In our opinion, Weiss Umwelttechnik fulfils this requirement in a special way. And thanks to the full maintenance, any problems are fixed extremely quickly and without any extra costs. Furthermore, it is important to me that the devices are calibrated by the manufacturer. I get everything from a single source and save time and effort."
* Jana Yatsuk is Market Manager Electronics & Energy at Weiss Umwelttechnik in Herbrechtingen.