Thermal Management
Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The
introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards
general illumination. The increased electrical currents used to drive the LEDs have focused more attention
on the thermal paths in the developments of LED power packaging. Thermal management for the solid-state lighting applications is a key design parameter for both
package and system level. The thermal challenges of these products in many applications will open new research
areas for engineers from chip level to system level thermal management.
The cornerstone of enabling LEDs to replace traditional light sources, such as incandescent and fluorescent bulbs, is to control the heat generated by LED chips, semiconductor devices. To gain high illumination, high electricity power input is needed and considerable heat energy will also be created by LEDs when emitting light under high power input. If the heat generated by LEDs can not be dissipated properly, if not completely, will cause the temperature of LED chips to highten. LEDs are made by semiconductor material and are sensitive to temperature. When the heat inside LEDs increases and temperature rises, LED chips and the doping element within will be altered and the performance of the fixture on which the LEDs are mounted will be compromised.
To ensure the reliability and durability of ultra-high-power LED lamps, keeping the junction temperature (Tj) low is always the key to achieve this goal. By maintaining the temperature of P-N junction low, the illumination degradation and the decaying of the LED emitters can therefore be extended.
The trend in the electronics industry of packing more power into smaller packages has created increasing thermal management challenges. Many of today's electronic devices require cooling beyond the capability of standard cast or extruded metal heat sinks. In many applications, heat pipes have enhanced heat sink performance and have become a mainstream thermal management tool.
To dissipate the heat, a copper heat pipe is attached to the bottom surface of the ceramic substrate on which the LED chips are laid on the other end. The ceramic substrate installed on every NeoPac emitter itself is also a technological achievement and ingenious design. Availing NeoPac patented technologies, the heat generated from the P-N junction of LED chips are directed through the copper heat pipe to the heat dissipation fins or heat sink on the outside of the fixture. Once the heat is transferred to the outside of the fixture, air convection takes over and carries the heat away.
A practical LED lighting device can strike a fine balance between performance and reliability. In lighting, the performance means the luminous flux output and reliability is the effective longevity of the device. The luminous efficiency of LEDs is soon expected to reach over 100 lumens/watt; this is approximately more than 6 times the efficiency of a conventional incandescent tungsten bulb. Since the reliability of LED lamps is also further assured by adopting NeoPac's thermal management techonolgy, the dream of popularizing LED as the light source for general lighting can be realized sooner than expected.