Light-emitting diode (LED) illumination continues to make headway in the indoor luminaire industry, where this solid-state lighting technology has obvious advantages over incumbent lighting methods. However, there are obstacles preventing more broad adoption of LEDs into the lighting market. These include complex technology; difficulty of replacement by end users, thermal management issues, and cost.
Enter the Zhaga Consortium. It formed for the purpose of developing standard interfaces to help address such issues.
To understand the role Zhaga plays, it is helpful to review how LEDs have evolved at the luminaire level. LED lighting utilizes several components different from those in traditional luminaires: the LED module, the control gear, and the heat sink. The LED module is the light source (like a lamp) and usually holds LEDs packaged on a circuit board with an electrical means for input power and signal. Usually, the input power to the module is low-voltage dc. The module typically gets its power from the control gear (or driver). The control gear is made up of electronics that convert line voltage to low-voltage dc with either constant current or voltage output. The control gear also protects LEDs from spikes and fluctuations on the input power lines. These two items, when discussed, together make up the “light engine” and can sit together in one housing or reside separately with a cable joining them. The heat sink, present in some lighting technologies, is much more common in LED applications, including spot and down lighting.
LED product development for general illumination initially followed two main paths: using traditional lamp bases for easy replacement, or integrating the LED module permanently to the heat sink of the luminaire. The first approach addresses the replacement market well, as the entire light engine is supplied in a “lamp” with an Edison base. But these products mostly rely on convection cooling and can’t conduct heat away from the LEDs. The second option of permanent integration provides the best performance, but makes field replacement more challenging.
LED products produce much less heat than traditional light sources, but the heat that is produced is highly concentrated at the LED itself. Therefore, it creates a small area of high temperature. LEDs have critical temperatures at which their life and color greatly degrade. Good luminaire design requires keeping reliably below this temperature while maximizing light output.
Traditional lamps with Edison bases, CFL pin-bases, GU-24, and so forth were not designed to help conduct heat away from an LED inside a lamp. Consequently, LED light sources that use these traditional interfaces must sacrifice either lamp life or lumen output. NEMA recognized this in its 2009 white paper, LSD 44 “Solid State Lighting—The Need for a New Generation of Sockets & Interconnects:”
“The use of existing sockets compromises the capability of solid state lighting. Existing sockets are sub-optimal mechanical and optical configurations. Existing sockets do not provide adequate thermal paths.”
Regarding the need for replacement, most, but not all, LED modules and light engines will last a long time. Luminaires designed with their LEDs permanently affixed have been considered acceptable because LEDs can last 50,000 hours and longer. But like all electronic products, they still have infant mortality rates and are susceptible to damage from broom handles, forklifts, and water leaks. Building occupants must be able to replace them if LED technology is to broadly succeed.
Additionally, specifiers are reluctant to install integrated light sources when they know building tenants may want to upgrade to higher efficiency, a different light output, or a different color temperature. 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 the same white paper (NEMA, LSD 44-2009):
“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…”
Edison-based LED products will be necessary in residential applications where there are billions of such sockets. The high-end integrated products are also important when performance is everything. In the middle are large commercial markets that need both replaceability and great performance. As people began to realize that thermal management and serviceability are important to the commercial markets, manufacturers introduced replaceable modules and retrofit kits with good thermal conduction paths. Many of these proprietary systems perform well, but each has a unique format from a different manufacturer. This approach brought the fear of obsolescence, as well as concerns about costs and lead time. Fortunately, the industry recognized that these factors could deter broad acceptance of LED lighting, and formed the Zhaga Consortium.
The creation of Zhaga
In 2010 a group of leading lighting companies met to form the Zhaga Consortium, an industry-wide cooperation aimed at developing standard specifications for the interfaces of LED light engines. The goal of the group is to enable interchangeability among 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 progress in several applications, including down lighting, spot lighting, street lighting, and ambient lighting (such as linear fluorescent). In each of these areas, Zhaga is defining four interfaces between the Light Engine and the luminaire: mechanical, electrical, thermal, and optical.
The Zhaga specifications only define the interfaces. This allows each manufacturer complete freedom to choose a technology to go inside its products. Formatting interfaces this way maximizes innovation in the industry, while assuring mating standards on which users can rely.
The modularity of Zhaga-compliant products will also lessen the challenge of incorporating LED technology into luminaires. Zhaga-based systems won’t need to be designed from scratch and components will be available from several manufacturers.
The Zhaga community defines interfaces and selects form factors via a multi-phased approach to assure all ideas are shared openly. The process starts by accepting proposals from members for a certain lighting application. Then the various proposals are evaluated by member companies that merge them into one standardized proposal that takes the best from each.
The specification then is documented so manufacturers can build prototypes to it for validation. This process helps assure a robust interface system that becomes a formal specification if the Zhaga membership approves it.Once the specification is approved, all changes must be compatible with earlier versions of the specification to maintain compatibility with future products. This requirement assures both luminaire manufacturers and end users that the interfaces from Zhaga can be relied on in the future.
Zhaga members have shown a sense of urgency and already have approved several specifications. Currently only members can review these specifications, but member companies are developing products to meet these specifications. Specifiers can be assured that these products will be compatible with replacement products developed in the future. The specifications will be made available for public download soon. Until then, the following describes the significant activity.
The first specification was approved in February 2011, for a socketable Light Engine with an integrated Control Gear. It is based on the Philips Fortimo Twistable, but has been adapted to meet such regional requirements as a universal input voltage (120/277 V). 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 promote the long-life and performance expected of LEDs, with the replacement as easy as a quick twist.
The second specification was approved at the June 2011 meeting. It covers the interfaces of an LED spotlight with the control gear located in a separate housing. The physical size and mounting of the modules is consistent, simplifying the task of replacement in the field.
At the September 2011 meeting, Zhaga members approved the third Zhaga specification. It describes the interface of a socketable spot light. The control gear of this spotlight engine again sits in a separate housing. Where the previously approved spot light engine was meant for direct screw mounting, this new specification is allows for a simple twist replacement of the module into the holder.
Currently in development are specifications for a light engine with a non-socketed linear module having separate control gear for indoor applications. Also in the works are specs for a non-socketed, street lighting engine with separate control gear.
Zhaga also established a task force early in 2011 to study how the dimming behavior of LED Light Engines can be specified such that they can exhibit interchangeable dimming behavior. The task force’s first priority is phase-cut dimming (i.e., cutting out a portion of the ac waveform as with triac dimmers). Zhaga does not plan to create a Zhaga specification for dimming, but will cooperate with NEMA to establish a dimming interface standard suitable for LED Light Engines.
Zhaga’s membership includes companies that traditionally manufacture lamps, ballasts, other system components, and luminaires. Agencies that test these products are members as well. Also on the membership rolls are electronics companies new to lighting, but with a long history in LEDs.
The output from this diverse group is expected to be robust standards that will be implemented in the market after thorough third-party testing. To maximize acceptance, Zhaga is putting into place a mechanism to inform other interested parties about these standards. In 2012, the Zhaga logo will begin to appear on numerous products to communicate compliance with Zhaga requirements. It will then be up to the marketplace to decide to what extent it desires high-performing, standardized products.