After Nick Holonyak invented the practical visible LED in 1962, the first commercial products were limited in brightness and only to applications such as red indicator lights and seven segment displays. In the 1970’s, yellow and green LEDs joined the family and were designed into products such as calculators, but still were not able to produce ambient light.

In the late 80’s to early 90’s, LEDs took large leaps forward, with the first blue LEDs, the advent of high brightness capability, and the use of phosphor coating to create white light. Technological improvements enabled even brighter LEDs, which enabled the move into progressively higher lumen applications: flashlights, signage, brake lights, traffic lights, and finally ambient lighting applications.

Today, LED lighting products offering more than100 lumens per Watt (LPW) are not uncommon and provide very efficient energy use compared to traditional light sources. These LED products are showing up in all types of form factors with some fitting into traditional sockets and some using custom interfaces. The challenge is to optimize LED Lighting performance in a product that is convenient for the building occupant.

FAQ #1: If LEDs last forever, why do we even care about end-user replacement?

The answer is that most of them last a very long time, but not all of them, so they must be replaceable. Many early LED luminaires were designed with the LEDs permanently affixed to the luminaire to maximize light output and thermal efficiency. This was considered acceptable because LEDs can last 50,000 hours and longer. LEDs are indeed capable of long service lives, but like all electronic products, they still have mortality rates and are susceptible to damage from broom handles, forklifts, and water leaks. They need to be replaceable by the building occupant if we want efficient LED technology to succeed in broad applications.

Also, when more efficient light engines become available, does it make sense to swap “lamps” or replace entire luminaires? The DoE’s Designer Roundtable on the subject cited replacement parts and lack of modularity as major drawbacks to LED adoption. NEMA recognized this in its 2009 white paper, LSD 44 “Solid State Lighting—The Need for a New Generation of Sockets & Interconnects”:

“Currently, in many LED fixtures, the LEDs are considered "permanent" and cannot readily be replaced in the field by end users or field service personnel. Some LED fixtures treat the LEDs as parts of sub-modules that could be replaced, but are not necessarily constructed in a manner for a “simple” swap without major disassembly of the fixture…. Growing experience with LEDs shows that failures do occur…”

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

Figure 1. Zhaga’s specification formulation process.

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 2. Downlight with light engine & holder (top) (Luminaire Courtesy of Pathway the Lighting Source). Light Engine (above) (Phillips) & Holder (Ideal)

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.

The Zhaga Process

Figure 3. Prototype LED spotlight module with separate control gear.

The Zhaga process uses a multi-phase approach to assure all ideas are shared openly so that specifications provide reliable interfaces while still maximizing the design freedom of LED technology. In the first phase, member companies present proposals for a product type for which they envision the need for standardization. There may be several proposals from different companies all for the same use applications. Then the members form a Task Force of volunteers who review each proposal and work to develop a specification framework that takes the best elements from each. The Task Force then asks the consortium members to vote whether they can form a Work Group to develop a specification.

Upon approval by the members, the specification begins to take concrete form. Once the specification seems set, the Work Group requests that manufacturers build prototypes to meet the draft specification. The prototypes are then reviewed for inter-operability and any issues found will be addressed with updates to the draft. Once the work group has a draft that is robust, they will submit it to the consortium members for a vote on whether to publish as a specification (Figure 1).

During the early period after the specification is approved, members may find improvement opportunities and will submit them to the work group for review prior to vote by the members. It is essential that any changes be compatible with earlier versions of the specification in order to reliably mate with products already available in the market. This provides assurance to the specifier community that the interfaces that come from Zhaga can be relied on in the future.

Approved Zhaga Specifications

Figure 4. Schematic view of a socketable LED module with separate control gear.

Zhaga members have already approved several specifications. The first specification was approved in February 2011 for a socketable light engine with an integrated control gear (Figure 2) for down lighting applications. It is based on the Philips Fortimo Twistable, but has been adapted to meet regional requirements such as versions that can support universal input voltage (120/277V and 347V in Canada). Several companies provided prototypes and input to the development of the light engine and mating holder. The design creates a large thermal interface between the light engine and heat sink to enable the long-life and performance expected of LEDs, with replacement as easy as a quick twist.

The second specification that was approved is for an LED spotlight module with the control gear located in a separate housing. As can be seen from the prototypes in Figure 3, the physical size, and mounting of the modules is consistent, so that replacement in the field is simplified.

The third specification that Zhaga members approved is for a socketable spot light. The control gear of this spotlight engine is again located in a separate housing. Where the previously approved spotlight engine was meant for direct screw mounting, this new specification allows for simple twist replacement of the module into the holder.

Current Status

As of the last meeting in November 2011, there were proposals for linear modules for both street lighting and indoor applications near completion.

Zhaga established a task force earlier in 2011 to study how the dimming behavior of LED Light Engines can be specified such that the light engines become interchangeable in their dimming behavior. The task force's first priority is phase cut dimming. Zhaga does not plan to create a Zhaga specification for dimming, but will cooperate with NEMA to establish a dimming interface standard that is suitable for LED light engines.

What Will Make Zhaga Successful?

Besides robust standards, Zhaga is putting into place both a mechanism to inform the user-public about these standards and also provide assurance through third-party testing that the products meet the requirements. In 2012, the Zhaga logo will begin to appear on numerous products to communicate compliance to Zhaga requirements.

About 80 participants from 40 companies from Europe, Asia, and North America continue to attend each Zhaga session. The Zhaga companies will continue their attention and sense of urgency throughout 2012 with the goal of creating peace of mind in the architectural and facility management communities that reliable LED products can be specified soon and will be available from many manufacturers well into the future.

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Lighting Technology Magazine

This article first appeared in the May, 2012 issue of Lighting Technology Magazine.

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