Zhaga Evolves: Focus on Component Standardization Drives New Book Development

In the five years since its inception, the international Zhaga Consortium has made rapid progress towards its central goal of standardizing a broad range of LED modules, LED light engines and related components.

The Zhaga specifications, known as Books, remove arbitrary and unnecessary variations in various properties, such as physical dimensions, making it easier for luminaire makers to base their designs on interchangeable components that are available from multiple different suppliers.

Products based on several of the Zhaga Books are already in common use in the global lighting market. Form-factors standardized by Zhaga, such as linear Book 7 modules or circular Book 3 modules, can be found in the portfolios of many leading lighting-component suppliers around the world. Meanwhile, Zhaga continues to develop new specifications that reflect the needs of luminaire makers and other stakeholders.

Meeting the Needs of the Market

Zhaga is currently going through a period of evolution, reflecting the changing demands of the global lighting marketplace. One major change for Zhaga is the creation of separate specifications for LED modules and LED drivers (also referred to as electronic control gear). This approach will enable luminaire makers to use different combinations of LED modules and drivers, according to their own unique requirements. Of course, this also requires that the electrical interface between modules and drivers is defined correctly. One consequence of this work is the creation of a new specification, entitled Book 13, which focuses entirely on LED drivers.

Zhaga has also made rapid progress in defining a new specification that covers chip-on-board (COB) LED arrays, in response to requests from many key stakeholders in the industry. As discussed below, the forthcoming Zhaga Book 12 will include a family of different COB module sizes.

Other new Books are also being developed by Zhaga to meet the requirements of the lighting industry, including both circular and linear light sources. One new specification, Book 14, will describe linear modules with cap-holder systems that enable end-user replacement. Other proposals include both driver-integrated LED light engines, as well as LED modules with separate drivers.

Zhaga has also undergone an exercise to ensure that its specifications only cover the properties necessary to enable interchangeability, while at the same time, allowing unrestricted possibilities for other aspects of component design.

Separate Books for Modules and Drivers

As stated above, Zhaga is now writing separate Books for LED modules and LED drivers. Previously, all Zhaga Books defined a complete LED light engine (LLE). Zhaga defines an LLE as a combination of one or more LED modules and a suitable driver, where the driver can be either separate from the LED module(s), or integrated inside the LLE. For LLEs with an integrated driver, Zhaga Books will continue to define the complete LLE.

However, for all LLEs where the driver and module(s) are separate, individual Books will be written that cover each different LED module type or family (Figure 1). The corresponding drivers will be described in a single new specification, Book 13. This change will be applied retrospectively to existing Books with separate modules and drivers.

Figure 1: For LED modules that are powered by a separate LED driver, Zhaga is writing individual Books for different LED module types. Meanwhile, a broad range of LED driver types are described in Book 13, some of which can be used in multiple applications to supply power to different LED module types

Interfaces 
The Zhaga Books are interface specifications, and each defines an LLE and/or associated components (including LED modules and drivers) by means of the mechanical, photometric, electrical, thermal, and control interfaces of the product to its environment. In many cases, the “environment” is an LED luminaire.

By specifying interfaces, this makes such LLEs or components interchangeable in the sense that it is easy to replace one LLE or component with another, even if they have been made by different manufacturers.

Figure 2: This schematic diagram gives an example of some of the interfaces defined by Zhaga for an LED module with separate driver. The dashed boundary lines show which interfaces are included in the module and driver Books, respectively. In this example, the LED module Book defines the thermal and mechanical interfaces with the luminaire’s heat sink, the photometric interface of the module with the luminaire’s optics, and also the mechanical and electrical interfaces with the driver

Previously, when Zhaga Books defined complete LLEs, all the specified interfaces were between the LLE and the luminaire. Now that separate Books are being written for LED modules and drivers, this changes the specific interfaces that are included in each Book. Figure 2 shows a schematic image of an LED luminaire containing a separate LED module and driver. The dashed boundary lines show which interfaces are included in either the module Book or the driver Book. Note that the scenario shown in figure 2 can vary from Book to Book.

Book 13 Defines LED Drivers

A typical LED driver can be used in multiple applications to supply power to different LED module types. The purpose of the Book 13 specification is to help luminaire makers and other stakeholders to compare the properties of different LED drivers. For example, a luminaire maker may wish to determine which drivers are compatible with different LED modules, and whether a driver will fit inside a given luminaire.

Two crucial aspects that determine if different drivers are interchangeable are the mechanical and electrical interfaces between the driver and module. The electrical interface is discussed in the next section of this article.

To enable the physical interchangeability of drivers in a luminaire, the mechanical dimensions must be clearly specified. To serve all applications, Zhaga Book 13 defines a range of driver form-factors. In addition to the maximum outer dimensions (demarcation) of the driver, each form-factor is characterized by both the position and number of mounting holes, and the position of the electrical wiring to the LED module and to the mains power source.

In total, across all form-factors, Book 13 includes 78 drivers with different dimensions. Two categories, designated Types A and B, have been developed by Zhaga. With a total of 27 different driver dimensions, Types A and B can serve nearly all applications, both for compact luminaires (Type A - 13 different size categories) and for areal lighting (Type B - 14 different sizes) over a very wide range of output powers. Zhaga recommends that the new form-factors in Types A and B should be adopted for new luminaire and driver designs.

However, the consortium also acknowledges that there are many existing driver products in the market, and these will require a long, gradual phase-out period. For this reason, a broad range of additional driver designations (types 1-8) are also included in Book 13.

Component Interchangeability and DMI

The new Book 13 is part of Zhaga’s efforts to enable LED luminaire manufacturers to use different LED modules in their luminaires without having to use a different LED driver for each module, or vice versa. Zhaga refers to this as “independent (or component) interchangeability” of LED drivers and modules.

With separate specifications for LED modules and LED drivers, this also requires that the electrical interface between modules and drivers is defined correctly.

To avoid duplicated efforts in the industry, Zhaga decided not to write a new specification for this driver-module interface (DMI). Instead, Book 13 references a specification written by MD-SIG. This is an external industry association which is not part of Zhaga, but in which several Zhaga members participate.

The DMI comprises two separate parts; the information interface and the power interface. Further information on the DMI and MD-SIG can be found in the article beginning on page 106.

Zhaga Standardizes COB Arrays

COB arrays are already in widespread use throughout the LED lighting industry, but different manufacturers offer a wide range of alternative sizes. For luminaire makers and other stakeholders such as suppliers of optics and COB holders, this creates problems and limits their options to use alternative products from different suppliers without changing their luminaire or holder designs.

In consultation with many interested parties, Zhaga was asked to standardize properties such as the mechanical dimensions of the module, the position of electrodes, and the diameter of the light-emitting surface (LES). The results of Zhaga’s work can be found in the first edition of Book 12, its specification describing LED modules that typically use COB technology.

The specification defines a family of six rectangular or square modules with a circular LES. The modules have the following dimensions: 12 x 15 mm, 16 x 19 mm, 19 x 19 mm, 20 x 24 mm, 24 x 24 mm, and 28 x 28 mm. Further details about Zhaga’s efforts to standardize COB LED arrays are documented in the article beginning on page 96.

Choosing the Right Parameters

Another recent activity by Zhaga members was to undertake a comprehensive review of the parameters included in each of its specifications. The goal was to ensure that the full parameter set of each Book includes all the characteristics necessary to enable interchangeability of LLEs, drivers, modules and other components.

The starting point was to create an exhaustive list of properties associated with the components described in each Zhaga Book. A number of luminaire makers and other stakeholders were asked to explain their requirements and preferences for each of the properties, in order to determine which properties should be included in each Book.

The characteristic properties of the LED light sources were assigned to one of three groups (Table 1). The first group includes properties that are not relevant to interchangeability, or are readily available elsewhere, and are therefore not included in the Zhaga specifications.

Table 1: Comparison of parameter types for LED modules and their relationship with Zhaga specifications. Zhaga only restricts a small number of parameters, enabling maximum design freedom. The parameters that are required on datasheets allow meaningful comparison of products

The second group of properties includes those that are considered essential to interchangeability, and are restricted by the Zhaga specifications, such that little or no variation is allowed. Many properties in this group relate to the mechanical fit.

The third group contains parameters where the value must be known in order for a customer to determine if one light source is interchangeable with another. However, Zhaga does not restrict the actual values of these properties. One example is luminous flux. Typically, for each Book, Zhaga will define a set of categories based on luminous flux ranges. A product can have any value of luminous flux, but the flux range must be stated on the datasheet. This enables a customer looking for closely-matched interchangeable products to select from alternatives that are in the same flux category.

Because Zhaga requires LLE manufacturers to provide a detailed set of parameters for each product, this allows luminaire makers to make meaningful comparisons and informed choices based on dependable data. However, it is important to note that many properties are not restricted by Zhaga. This promotes design freedom by only restricting those parameters that are essential to ensure interchangeability.

Certified Products

Products that have been tested by an independent testing lab, and are fully compliant with all the requirements of one of the Zhaga Books, are allowed to carry the Zhaga logo. This symbol conveys the assurance of interchangeability, but also means that the product is traceable through Zhaga’s online Certified Products Database [1].

The database has been updated recently, and now has a very comprehensive search functionality. This allows potential purchasers to compare products, based not only on which Book the product belongs to, but also by looking at various key properties. For example, when selecting a Book 3 LED module, the user can not only choose the desired LES category, but can also compare luminous flux, color-rendering index, correlated color temperature and other properties.

New Books and Extended Families

Book 9
Zhaga extended its library of specifications in June 2015 with the publication of Book 9. Compared with earlier Books, which are aimed at professional lighting applications, Book 9 represents a shift towards the consumer sector. Book 9 LLEs comprise a non-socketable LED module with a ring-shaped light-emitting surface (LES) and a separate LED driver (Figure 3). The LED modules are small in size - the LES diameters are 12 mm or 25 mm - with simple construction and a low profile (4 mm height). The light output is typically in the order of several hundred to around one thousand lumens. These features mean that Book 9 LED light engines are highly suited for use in LED luminaires for consumer lighting applications, such as small spotlights, track lighting and other compact luminaires. However, Zhaga does not restrict the applications that can be addressed.

Books 3, 10 and 11
Zhaga is building on the success of Book 3, which defines 50-mm-diameter modules for spotlighting and related applications. The range of spotlight modules is being extended to both larger (75 mm diameter) and smaller (35 mm diameter) sizes, which are designated Book 10 and Book 11, respectively. Book 11 was published by Zhaga in July 2015. In fact, due to the similarities in these modules, Zhaga has already decided to merge these Books into a single specification.

Figure 3: There are two categories of Book 9 modules (left). These have a ring-shaped light-emitting surface with a diameter of either 12 mm or 25 mm. Book 11 modules (right) have an overall diameter of 35 mm, compared with 50 mm for Book 3 modules

Book 7
LED modules using the form-factors in Zhaga Book 7 are now a common sight in the market. Included in Book 7 is a scaled family of linear modules, with lengths of 280 or 560 mm and widths of 20, 40 or 60 mm. Recently, two additional square modules with sides of 380 and 560 mm have been added to Book 7. Such modules are suited for indoor lighting applications such as office lighting.

Book 14
The latest proposal to reach the Book-writing phase is Book 14, which will define specifications for linear, socketable (tool-less replaceable) light engines and modules with a cap-holder fit system.

The Book will include versions with integrated drivers and versions with separate drivers. Three length designations (lengths of approx. 1400 mm, 1120 mm and 560 mm) are likely to be included.

New Proposals

Zhaga is now reviewing a series of new proposals from its member companies:

• Planar, large-diameter, circular LLEs (with integrated driver) for potential use in flat, circular luminaires with a homogeneous, low-glare surface

• Rectangular LED modules (with separate driver) for use in combination with lens plates, in outdoor lighting applications

• Circular, small-diameter, spotlight-type LLEs (with integrated driver) for use in applications such as compact spot-type indoor luminaires (e.g. track lights)

These proposals were made after Zhaga identified opportunities and set priorities for new specifications that will provide most benefit to the LED lighting industry.

Conclusions

By listening to feedback from stakeholders, and responding in a timely and efficient manner, the Zhaga Consortium is continuing to provide an important contribution to the ongoing growth and development of the LED lighting industry. Changes have been put in place that will enable component interchangeability of LED modules and drivers, as requested by the market. Zhaga is also expanding its portfolio of specifications for LLEs, modules and drivers, and is building scaled families of interchangeable products that provide choice for luminaire makers alongside the benefits of standardization.