Connected Lighting | Standardization | LpR Article | Smart Lighting + IoT | Resources | Zhaga | Dec 12, 2018

Zhaga Enables Mechanical IoT-Upgradability for Outdoor LED Lighting Fixtures

LpR 69 Article, page 42: The Zhaga Consortium is a global association of lighting companies that is standardizing LED luminaire components interfaces. The latest specification from Book 18 defines a standardized interface between outdoor LED luminaires and modules for sensing and communication. Dee Denteneer, Zhaga Secretary General, explains how the New Book 18 helps bring the Internet of Things to the outdoor lighting market via smart, upgradeable, future-proof fixtures.

Zhaga’s first concrete contribution to IoT is the recently completed Book 18 Ed. 1.0 that specifies the mechanical interface between outdoor LED luminaires and extension modules (Figure 1). This specification makes it easy to upgrade conforming outdoor LED fixtures by adding or changing 24 V modules that provide sensing and communication capabilities. This adds flexibility and value to these luminaires and gives assurance to our end-customers that the luminaires are future proof.

In this article, we first introduce connectivity interfaces, their use in smart city scenarios: stressing the value of standardization, interoperability, and certification. Next, we zoom in on the technical features of Book 18 Ed. 1.0, which defines the mechanical aspects of the interface; including topics like vendor differentiation and a benchmark against NEMA C136.10. Lastly, we sketch the path towards Book 18 Ed. 2.0, which will additionally specify the electrical and control aspects of the interface, covering our collaboration with the Digital Illumination Interface Alliance (DiiA) and how to move from a mechanical interface to a plug-and-play interoperable proposition, driving growth for the lighting industry.

Smart City Scenarios

The lighting industry is keen to play a central role in the business that comes along with emerging smart-city propositions, and definitely has a right to this role because of the access to the power grid offered by outdoor luminaires and their high density in cities.

Yet lighting is also confronted with a smart-city dilemma. There is still huge uncertainty concerning the preferred business propositions that will transition the smart city from promise to reality, and the connectivity and sensing technologies that are to be included in outdoor luminaires. Moreover, these propositions may very well depend on local conditions and preferences and may change over time, as may technology preferences. And yet we are installing outdoor LED luminaires right now.

Failure to resolve the dilemma hampers the installation of smart luminaires, and, consequently, prevents the lighting industry from assuming a central role in the smart city. Our right to play a role may then be superseded by faster movers in other industries.

IoT Upgradeable Fixtures

This smart-city dilemma is resolved by means of an interface that sits between the luminaire and an external “intelligent” or “connected” extension module (Figure 2).

Figure 2: A well designed interface between the luminaire and an external intelligent or connected extension module makes the luminaire upgradeableFigure 2: A well designed interface between the luminaire and an external intelligent or connected extension module makes the luminaire upgradeable

Such an interface, if well-designed and meeting smart-city requirements, future-proofs the luminaire as it enables upgrades achieving conformity of the luminaire to new needs and insights. It thus breaks the impasse and allows for the installation of smart-ready and upgradeable luminaires right now.

Several deployments are possible with this interface. For instance, a luminaire may be installed without any sensing or communication technology present. As needs arise, new communication or sensing functions can be added by mounting an appropriate external module onto the luminaire (Figure 3). Alternatively, the modules may be included at installation time based on a communication technology, A. As time passes by, communication technology A will be superseded by a faster revision or by a competitor technology B. The module can then be unmounted and replaced by a new module that implements this improved technology.

Figure 3: IoT upgradeable luminaires future proof the luminaire by enabling deployment scenarios in which the sensor or communication functions are added, or replaced, during the luminaire lifetimeFigure 3: IoT upgradeable luminaires future proof the luminaire by enabling deployment scenarios in which the sensor or communication functions are added, or replaced, during the luminaire lifetime

To enable smart city scenarios and IoT upgradeable luminaires, it is mandatory that the interface is developed as a standard that supports interoperability between luminaire and extension module.

The interface should enable interoperability to ensure that the external module will work with the luminaire, whenever it fits. This feature is essential for scenarios in which a luminaire is upgraded in the field in minimal time by a non-lighting expert. The interface should be a standard to drive the acceptance and installed base of IoT upgradeable luminaires. A large installed base of IoT upgradeable luminaires will drive the development of smart modules that match the luminaires, which will add value to the luminaires and drive the installed base. It seems impossible to get these reinforcing dynamics and scale without a standard.

Most importantly, without a standard, customers will not be convinced that the luminaire can indeed be upgraded for its lifetime at reasonable costs in a multivendor eco-system.

This idea is so natural that it seems hardly likely that it has not already been picked up elsewhere. In fact, it has and there is a successful predecessor in the existing ANSI/NEMA standard C136.41-2013. However, Zhaga has modernized the concept and redeveloped the concept for the LED era.

The Value of Standards, Interoperability, Certification

The value of standards for the high-volume lighting businesses has been the initial driving force behind Zhaga [1]. In its more recent evolution, the organization has widened its scope to better address interfaces for smart components, such as sensors and connectivity modules, its support of emerging business propositions from IoT and service economy, as well as its commitment to interoperability [2].

Zhaga has always promoted a restrained approach to standardization specifying only those aspects of an interface needed to support interoperability: Remove arbitrary variation in interface parameters that do not add value for the customer but leave ample room for vendor differentiation.

Furthermore, testing has also always been an integral part of the standardization. This has been included in so called “round robins” during specification development as well as in testing and product certification. The availability of testing and a logo program is a key asset to demonstrate interoperability, which is essential for specifications targeting non-lighting specialists as well as product companies from different industries.

Phase 1: The Mechanical Interface and Vendor Differentiation

Street lighting is a large part of the outdoor lighting market and a focus point for smart cities, yet has largely been ignored by standardization, with only North America having a published standard for a connection between a luminaire and a control node. The Book 18 Ed. 1.0 provides an alternative interface. While defining the mechanical fit and designation of the four electrical contacts, many of the non-critical aspects are not restricted by the specification. Design freedom is therefore still provided for a manufacturer to design for unique application complexities and thereby the specification allows for vendor differentiation.

Figure 4: Positions of the reference point, the reference plane and reference axes of the Receptacle and ModuleFigure 4: Positions of the reference point, the reference plane and reference axes of the Receptacle and Module

By 2019, 91% of all newly installed streetlights will be LED. Book 18 Ed. 1.0 is an updated solution specifically for the new world of LED lighting. It defines the mechanical interface between a module (control node) or cap and receptacle. As stated the connector is a four-pin interface. A DALI 2.0 inter luminaire communication bus has been selected as the protocol to provide 2-way control between modules and an ECG (Electronic Control Gear). Therefore, using two of four the pins. The system doesn’t take advantage of DALI’s ability to be polarization free, but instead sees a greater benefit to have a 24 V auxiliary power supply share its 0 V line with DALI, reducing the pin count and reducing the cost of the connector. Although the DALI bus is a powered bus, being able to power a device with a load up to 250 mA, the 24 V pin will allow devices with greater power demands to be connected. The fourth pin is a digital I/O and the detailed specification in phase 2 will define its use.

Mechanically the book has been carefully written to define only the interface features. Though the Book 18 Ed. 1.0 product does speak to the ANSI C136.10 design, having curved flag shaped contacts and a rotary locking mechanism. That is where the similarity ends: It is not designed for a power switching architecture, but instead allows designers to focus on compact elegant control nodes. After all, the locking interface and also the overall diameter of the connector is approximately only 30 mm in diameter. This small diameter, just by the area it takes up, makes it much easier to seal to the luminaire. The book doesn’t restrictively define the seal, instead defines it by a mating surface and a keep out zone. It does allow for designs where a single seal can provide ingress protection between the receptacle, luminaire and module. Rather than a solution that needs a seal between receptacle and luminaire and a second seal between receptacle and module. The seal is not restrictively defined, as to allow for seals that are designed to work with heavily contoured luminaires, not just flat surfaces. This does not compromise the quality of the product, which the book delivers, as the certification process tests for product compliance.

The locking features also act as a key, making sure that a module only fits to a receptacle in one orientation. Not only does this mean that contacts cannot be misaligned, but where a module needs to have a specific orientation to the streetlight and hence the roadway, this is also realized. This is a necessity for such applications like motion sensing. Contained in Book 18 Ed. 1.0 is a detailed description of how a manufacturer must align a receptacle with respect to the luminaire. Ensuring that whatever functionality the module has, it can be realized on multiple designs and multiple manufacturer’s streetlight.

The seal example is just one way that differentiation can be achieved. For the module and sealing cap, again the interface is defined, but outside a keep out zone for the diameter, there is design freedom. So, if you are adding rigidity to survive an IK09 impact test or features to blend a module into the luminaire, the Book 18 allows for it. For the receptacle the design freedom is around how it is electrically connected to the internals of a luminaire. Whether flying leads or a “connectorized” solution is needed, again Book 18 allows for it.

Despite of the strong specification it also allows the industry to have product differentiations, which is often achieved through innovation. Book 18 Ed. 1.0 doesn’t limit this innovation. Instead identifies only the aspects of the interface that guarantees the fit system, meaning that any Book 18 compliant module will fit with any luminaire that has the Book 18 receptacle. Fit systems are the corner stone of any ecosystem allowing upgradability and serviceability through interoperability.

Phase 2: The Power and Control Interface

Phase 2 of Book 18 will be Zhaga’s first specification offering a fully interoperable solution. To ensure true interoperability between modules and drivers of various manufacturers, the mechanical interface and electrical pin assignment needs to be complemented with the power and control interface specification. As indicated before, the 4 pins of the connectivity interface are the 24 V DC power supply, the DALI control lines and a so-called general digital I/O pin which will be reserved for future use are not part of Book 18 Ed. 1.0.

The 24 V DC power is an auxiliary supply for demanding connectivity or sensor applications requiring average power levels up to 3 W, allowing pulsed mode operation up to 6 W. The power supply specification also describes the start-up sequence including maximum start-up time and supply current capabilities during start-up.

For the interface specification of the two DALI pins, Zhaga has set up a liaison with the Digital Illumination Interface Alliance (DiiA) to align specification in Book 18 Phase 2. From a specification organization point of view, the DiiA has split the related interface protocol into 4 different parts, describing the following aspects: integrated DALI power supply, asset management of the luminaire, energy reporting and diagnostics.

Benchmarking: NEMA ANSI C136.41-2013

Book 18 Ed. 1.0 offers a number of advantages compared with the existing ANSI/NEMA standard C136.41-2013. These advantages are directly related to the underlying system architecture, which is based on a low voltage driver - module interface. This non-mains interface enables a more compact form factor of the connector, leading to a significant size and cost reduction of the corresponding receptacle (i.e. diameter reduces from 66 to 30 mm). The receptacle also allows for more flexible mounting options such as bottom and side mounting of the modules (Figure 5). This will initiate many more new connectivity but also sensor applications, such as e.g. movement detection under the pole.

Figure 5: The Book 18 interface design well supports external modules that are mounted underneath the luminaireFigure 5: The Book 18 interface design well supports external modules that are mounted underneath the luminaire

This architecture also removes redundancies at system level, removing the need for double surge protection and multiple power conversions from mains to low voltage DC in both driver and controllers. In the preferred architecture functions like energy metering (1% accuracy), asset management and diagnostics are covered by the driver. As a result, the luminaire integration is simplified as less wiring and components are required.

Next to above-mentioned benefits, guaranteed interoperability of modules and drivers is one of the most important promises. The specified DALI-based interface ensures that driver and controllers speak the same controller language. On the contrary, the C136.41 specification leaves room for different dimming standards (i.e. DALI and 0-10 V) leading to interoperability issues when exchanging or upgrading luminaires in the field.

In short, the Book 18 interface specification offers luminaire OEMs and smart cities companies a compact, cost sensitive and easy-to design in solution. In addition, the single gasket receptacle design offers a robust and waterproof solution for a wide range of outdoor luminaire applications. True interoperability is thereby the most important promise.

A Growing Eco-System

Although the Zhaga vision on IoT upgradeable outdoor luminaires is still unfolding, early signs of success are already visible. Products are available that conform to the mechanical interface, and that support the development of IoT upgradeable luminaires as well as external modules. Products in scope are receptacles along with caps to be integrated with the luminaire. A second set of products support the development of external modules and comprises base plates on which to integrate the sensing and connectivity boards, along with domes (Figure 6).

Figure 6: Products are becoming available that support the development of both luminaires: receptacles and seals, as well as the development of external modules: base plates and domes functions are added, or replaced, during the luminaire lifetime (Credits: TE Connectivity)Figure 6: Products are becoming available that support the development of both luminaires: receptacles and seals, as well as the development of external modules: base plates and domes functions are added, or replaced, during the luminaire lifetime (Credits: TE Connectivity)

The certification program for these products is now open and first products have been certified. As another early sign, there is reference to the Zhaga interface specification in specifier documents [3], and a lot of interest has been expressed by other specifier organizations. Meanwhile, a number of luminaires are already available that support this interface. Also on the market are several external modules supporting a variety of sensing modalities, such as motion sensing and light measurement, or light management via a number of connectivity technologies, such as 3G and LORA.


Zhaga is in the process of implementing its vision for the outdoor connectivity interface, as described in this article. There is a strong belief that this connectivity interface will enable growth for the lighting industry, secure a central role for lighting in the smart city, and add value for all players along the lighting value chain. The early signs of adoption provide concrete proof points for the success of this vision. Following a similar vision for indoor lighting, a white paper on this topic is available [4], and a working group has recently been established. Specifications are in the making to implement the New Zhaga’s vision for other components in the luminaire as well.

[1] Dee Denteneer; Zhaga Gets Smart: Addressing the Industry Need
     for Smart Lighting and Standardized LED Components;
     LED Professional Symposium 2016, Bregenz
[2] Dee Denteneer: Introducing the NEW Zhaga: Smart standards.
     Smarter lighting, LED Professional Review, Issue 68, July/Aug 2018
[3] IPWEA, Model Public Lighting Controls Specification: Street lighting
     and smart controls programme version 1.0, Institute of Public
     Work Engineering Australia, 2018
[4] Jan de Graaf et al. The NEW Zhaga develops connectivity
     interface standards for indoor luminaires; Zhaga white paper, 2018