Design of multichip LED module for lighting application

Abstract

White LED is well known as a promising device for solid state lighting. It has the advantages of long life, good endurance of heavy impact, no mercury containing and potentially high efficiency. However, light output from a commercial LED lamp is usually less than 0.1W, which is very small if compared with traditional light sources. In order to get enough light output from LED devices, a big-lamp or cluster, which is packed from dozens or hundreds of LED lamps, is necessary not only for outdoor display but also for lighting applications. Some problems were encountered during high-density assembly in a big-lamp. Because of the bad heat conductivity of the epoxy, the more LED lamps are used in the big-lamp, the poorer heat dissipation will be. On the other hand, it is difficulty to manufacture a big-lamp in good alignment of every LEDi¦s during the package. One of the ways to solve this problem is to use a big LED chip instead of many small lamps. Nevertheless, to use those big chips always companions 10-25% loss in the external quantum efficiency. And, the bigger the chip is, the larger the loss will be. Highly concentrated heat will be another issue for the big chip package. In this article, we will present a new design for the package of multi-chips LED module, which could assemble dozens of LED chips with the normal size for lighting purpose. Optical devices, including reflector and focusing lens, and heat considerations are considered in the design of the new module. The prototypes of the new modules have been made. The current of maximum light output (Cmax) is about 2 to 3 times superior to conventional lamps. Under the condition of normal driving current, a 4.5 W LED module have an output intensity of 164 cd. Combining 4 LED modules will be comparable with a conventional 20 W Halogen lamp.