LED Street Light has been widely used in industrial area, commercial area and residential area. Lacking of an identical standard in LED testing methods is always the biggest problem for LED industry. Once promoting a new product, manufacturers can only set the parameters though some theoretic values. The most common example is the working time. Most of product specifications will set this parameter as 50000 hours. As a matter of fact, this is a theoretic value rather than testing result, calculated though another parameter (light attenuation) in ideal conditions. In practices, it is impossible for any LED products to constantly work for nearly 6 years without any defects. LED manufacturers and research institutions have a lot of disagreements in setting parameters. Customers often complained that their LED products cannot work in the described conditions (insufficient light intensity, higher temperature). This situation, to a large extent, restricted the development of domestic LED industry. In following sections, we are going to discuss some international standards for LED testing methods: electrical property, optical property, switching feature, color property, thermal property and reliability.
Electrical Property: LED is a kind of uni-polar PN junction diode. The voltage-current characteristic can be divided into two parts: forward bias and backward bias. Thus electrical properties of LED high bay include maximum forward current, maximum forward voltage, backward current, backward voltage. LEDs must work under a normal current (theoretically 20mA). We can also obtained maximum working power tough these electrical properties. LED electrical properties should be measured under constant voltage and constant current, by using multimeter.
Optical property: similar to other lighting sources, LED optical properties include luminous flux, lighting efficiency, radiation flux, radiation efficiency, light intensity, light distribution and spectral parameters, etc. We will introduce the testing methods of these parameters in detail.
Luminous Flux and Lighting Efficiency: there are two different ways in measuring luminous flux: integrating sphere method and variable angle photometric method. The later is the most accurate measuring method, but costs much more time. Thus, in normal conditions, scientists and technicians tend to use integrating sphere method to measure luminous flux of LEDs. Integrating sphere method also has two different measuring structures: 1. LED is settled in the middle of the sphere; 2. LED is settled on the edge of the sphere.