FAQ #2: If LEDs are so efficient, why is thermal management important?

Figure 2. Downlight with light engine & holder (top) (Luminaire Courtesy of Pathway the Lighting Source). Light Engine (above) (Phillips) & Holder (Ideal)
It does seem contradictory that a high efficiency product needs its heat output well managed. Actually, LED products produce much less heat than traditional light sources. The difference is that the heat produced in an LED product is highly concentrated at the LED itself and thus creates a very small area of high temperature. The LEDs have a critical temperature at which their life will be greatly affected. Good luminaire design requires a product that reliably stays below this temperature and yet maximizes light output. Traditional lamps with Edison bases, or CFL pin-bases, etc. were not designed to help conduct heat away from an LED inside a lamp. Consequently, LED light sources that use these traditional interfaces have to sacrifice either lamp life or lumen output.

So, LED product development for general illumination initially followed two different paths: 1) using traditional lamp bases for easy replacement and 2) using integrated luminaires for great performance. Then came LED modules. Modules allowed easy replacement and also were designed to provide a good thermal conduction path away from the LEDs. These seemed to bridge the missing gap, but then market acceptance was slowed since each was a proprietary system, with a unique size and mounting.

The Creation of Zhaga

Figure 3. Prototype LED spotlight module with separate control gear.
This brings us to March of 2010, when a group of lighting-related manufacturers from around the world first met to form the Zhaga Consortium. Zhaga is an industry-wide cooperation aimed at the development of standard specifications for the interfaces of LED light engines. The goal of the group is to enable interchangeability between products made by different manufacturers. As the Zhaga website states:

“Interchangeability is achieved by defining interfaces for a variety of application-specific light engines. Zhaga standards will cover the physical dimensions, as well as the photometric, electrical and thermal behavior of LED light engines. Zhaga is established for the benefit of the consumers and professional buyers of light engines and luminaires, in the expectation that standardization will prevent market fragmentation into incompatible products. Zhaga standards will increase the confidence to specify and purchase LED products that will be easily replaceable and commercially available, while continuously enjoying the performance upgrades that LED technology enables. In addition, this will foster innovation and competition in the application of LED lighting in general.”

Zhaga companies have already made great progress in several applications, including down lighting, spot lighting, street lighting, and ambient lighting (such as linear fluorescent). For each of these, Zhaga is defining four interfaces between the light engine and the luminaire: mechanical, electrical, thermal, and optical. The Zhaga specifications only define the outside of LED light engines. Zhaga treats light engines as a “black box”, with defined interfaces that do not depend on the technology used inside the light engine. This enables maximum innovation within products, while assuring a mating interface on which users can rely.

In order to create standardized LED options that can be specified in the near future, the Zhaga Consortium is working at an incredible rate. In less than two years, the Zhaga companies have already met 13 times and have planned 6 more meetings in 2012.