Intra-luminaire interfaces pave a path to a smart LED luminaire future (MAGAZINE)

While external or inter-luminaire networks and protocols are often top of mind for solid-state lighting (SSL) industry professionals contemplating connected lighting and the potential of SSL as an Internet of Things (IoT) backbone, it might be the intra-luminaire interfaces that enable an economical and logistically-simple approach to smart luminaire architectures. Indeed, standardization of internal communication buses and protocols could enable the industry to deliver more smart, LED-based lighting products or at least luminaires that could easily have such smarts added in the field. Moreover, a standards-based approach could enable entry-level functionality such as dimming and more advanced applications such as real estate space optimization or indoor wayfinding.

Indeed, we at LEDs Magazine have covered smart and connected lighting a lot going back to 2010 or so with articles ranging from application scenarios to choices of networks and protocols. The most common themes have in fact been applications and network choices, and we have regularly maligned the possibility that the lack of a ubiquitous inter-luminaire network — one that connects luminaires, external sensors, control panels, central management systems (CMSs), and more — is stymieing the adoption of connected lighting. Manufacturers and lighting designers/specifiers struggle with a bewildering set of choices such as Bluetooth Mesh, Zigbee, and more on the wireless side; and Power over Ethernet (PoE), DALI (digital addressable lighting interface), power line communications, and proprietary systems on the wired side.

And ultimately, the industry does need some clarity on inter-luminaire networks. Still, it’s unlikely that the sector will settle on a single selection. PoE mighty be perfect for a new construction project such as The Edge building to which Signify supplied PoE technology in Amsterdam (Fig. 1), while retrofits have far different needs. So luminaire developers and manufacturers need a way to support some amount of flexibility in terms of internal luminaire architecture while minimizing the technology and logistics challenges. And it’s increasingly clear that the path forward is standardization of communications between subsystems inside the luminaire — standardized intra-luminaire networks or buses and protocols.

Engineering simplicity

Now explain the need of adding connectivity to an LED-based luminaire to an electronics engineer and give that engineer a blank sheet of paper, and we can speculate on what a proposed architecture might entail. LED luminaires already have LED drivers integrated within. Many of those drivers already have some sort of microcontroller (MCU) or microprocessor inside. So it does logically follow that the simplest path forward might be enhancing the driver design with a more powerful MCU. That MCU would probably have internal support for Zigbee or Bluetooth Mesh. And the engineer could easily add interfaces to sensors for occupancy, ambient light, temperature, and more. Such thinking would surely provide the lowest-cost luminaire architecture — so long as everyone wanted to buy the same feature set in their lighting products.

But consider the logistics nightmares. We recently held a webcast presented by Karl Jónsson, who is currently working as an SSL industry consultant and previously led the technology development for the Tridonic net4more smart lighting platform. That webcast will be available on demand until sometime in October 2019. Moreover, Jónsson was involved in some of the earliest connected lighting installations around the globe.

Geography and markets

Jónsson broke down both the market for intelligent controls in the US and Europe, and the luminaire architectures that could meet those demands. Ironically, the markets and demands aren’t necessarily as they would first seem. Conventional wisdom holds that the North American market has adopted relatively simple dimming using 0–10V controls while Europe has been more aggressive in adopting a fully-digital, bidirectional interconnect in DALI.

According to Jónsson, however, the majority of the LED luminaires sold in Europe have no dimming features today. DALI is widely used as the inter-luminaire interface in the minority population of dimming-capable products. In the US, the vast majority of LED luminaires being sold support dimming, but most all today are based on the 0–10V technology. That simpler interface is unidirectional and does not support some of the applications that we will address later.

There are further differences in requirements based on geography, according to Jónsson. Some are regulatory in nature, such as whether it’s allowed in a region for a service technician to open an installed luminaire and add a retrofit sensor or communication module. And safety standards vary around the globe.

Fractured demand

What you should take from this discussion is that the market for smart luminaires is destined to remain a highly-fractured market. In part, the plethora of inter-luminaire connectivity options will drive that reality. But other factors will contribute as well, ranging from regulatory policy to what facility managers and building owners will pay for in-luminaire features.

Already today, luminaire manufacturers deal with the logistics headache of a fractured market that only starts with the requisite differences for models destined for different places around the globe. But customers have different requirements in dimming support and other controls and support for operation in harsh environments. The manufacturers — and the supply chain including distributors, retailers, large end users such as municipalities, and more — have to deal with far too many models or SKUs (stock keeping units).

FIG. 2. The Signify Xitanium SR (Sensor Ready) driver family uses an extended version of the DALI bus to power and bidirectionally communicate with sensors. (Photo credit: Image courtesy of Signify.)

Jónsson pointed out that integrating connectivity and sensor-specific features into drivers would only exacerbate the situation with more driver models leading to yet more SKUs. And even discrete sensors and other functionality further adds to the problem.

Consolidating connectivity and sensors

The SSL industry has moved to simplify the situation through integration of sensors and connectivity and essentially control at the luminaire level into one modular device with that module connecting to the driver — whether the driver be the simplest 0–10V dimming driver or a more intelligent programmable unit with bidirectional communications. For example, Signify (formerly Philips Lighting) has offered its Sensor-Ready (SR) Xitanium driver family for several years (Fig. 2). We covered that program after the company featured it at an industry IoT event back in 2017. Signify offers a small (read manageable) number of sensor/connectivity SKUs that can be combined with the Xitanium drivers in a luminaire development. Those options were very well described in a recent webcast that will only be available on demand through June. The sensor models vary based on the connectivity and sensor capabilities integrated.

Osram has taken a similar path in supporting connected luminaire designs with its Optotronic drivers enhanced with the DEXAL (data exchange for advance lighting) interface that we wrote about after LightFair International last year. We also did a video interview from LightFair covering the SensiLUM modular connectivity/sensor product announced last year. SensiLUM (Fig. 3) uses the DALI-based DEXAL interface to connect with the Optotronic drivers.

At first the concept of integrating intelligence, connectivity, and sensing — separate from the driver — seemed like a backwards concept. But once you consider the logistics involved, you begin to understand why the architectural decision makes sense.

Intra-luminaire options

So let’s consider more about the benefits of an integrated module and options for intra-luminaire connectivity. We published a contributed feature last year by TE Connectivity that discussed the benefits. That article focused foremost on having a variety of different sensors all tied to one MCU that in turn would connect to a driver circuit. The article made the point that the integrated module made it such that the format of data from every sensor could be consistent, and the design would be simpler from a hardware perspective relative to a system with disparate analog and digital interfaces connected to the various sensors.

In the above case, TE Connectivity advocated for using the I²C interface for connecting the sensor module and driver circuity. But I²C is an industry-standard interface used to connect ICs in complex electronic designs. It is typically used on a printed circuit board (PCB) to connect ICs and not routed over cables. I²C could potentially be used across cables but with a very limited cable run between the driver and a sensor module. I²C is probably not ideal with separate driver and sensor modules.

FIG. 3. The Osram SensiLUM sensor is based on an intra-luminaire interface that the company calls DEXAL, but that proprietary implementation has a DALI basis. (Photo credit: Image courtesy of Osram Digital Systems.)

Meanwhile, European driver and light engine manufacturer Tridonic entered the US market at the beginning of 2017 and also announced its net4more connectivity platform at the same time. The focus of the company’s marketing efforts at that time was an Internet Protocol (IP)-based inter-luminaire network with every node having its own IP address. But the company also developed an intra-luminaire, bidirectional bus that it calls un:c. That net4more architecture separated the driver from sensors and connectivity and Tridonic developed modules for those functions that connected with a driver via un:c. That architecture also supported sensor modules integrated in the luminaire or modules mounted near a luminaire — say, an occupancy or ambient light sensor mounted directly in the ceiling.

Standards-focused design

Also in the first half of 2017, connected lighting specialist Enlighted launched the IoTReady Alliance with Tridonic as a partner. At Strategies in Light earlier that year, Enlighted CEO Joe Costello had warned the industry that manufacturers shipping luminaires with no upgrade path to connectivity and intelligence could retard the smart building revolution by a decade. Costello reasoned that connected LED lighting was the backbone needed for smart lighting. Yet once energy-efficient LED lighting with no connectivity was installed in a building, no subsequent retrofit would be contemplated for a decade. The IoT-Ready Alliance was focused on getting a standardized connector and interface in luminaires, whether lighting would be installed with intelligence up front or retrofitted later with a connectivity/sensor module.

It turns out that quite a few industry organizations and commercial manufacturers were moving in the same direction. And the central focus for intra-luminaire connectivity was again at first a seemingly unlikely candidate — DALI. As mentioned earlier, DALI had been primarily an inter-luminaire network. But it included some capabilities that could be enhanced for use inside the luminaire. The protocol defined for DALI had standardized commands for dimming andmore that could easily be extended for the communication needed inside a luminaire.

Indeed, both the Signify SR and Osram DEXAL schemes were based on DALI, with the companies adding to the protocol to support, for instance, the ability to retrieve operational data from a driver — for example, power used, hours of operation, or operating temperature. Moreover, the companies devised a way to use the two-wire interface to simultaneously supply the low levels of power a sensor module might need to operate and to carry bidirectional data.

Standards bodies and industry organizations

Fast-forward to the present, and several standards bodies and industry organizations have become involved in enhancing and extending DALI for intra-luminaire usage. The Digital Illumination Interface Alliance (DiiA) took over promulgation of the DALI technology and standard in 2017. The organization first ratified DALI-2 that added the commands and data structures allowing connectivity of control devices or sensors that could be read as opposed to what had been primarily a one-way flow of commands to control a luminaire. The ability to read data would also allow a CMS to access diagnostic data from a luminaire or discern actual energy usage.

Subsequently, the DiiA developed an interoperable scheme for powering sensor and communication devices from the bus that was key to intra-luminaire applications. That work is defined in the DALI Part 250 – Integrated Bus Power Supply specification — and was completed in collaboration with NEMA (National Electrical Manufacturers Association) in North America, bringing standardization of the DALI physical layer into ANSI as C137.4. DiiA will also turn its work over to the IEC for standardization in Europe.

FIG. 4. Enlighted was perhaps the first company to integrate multiple sensors and connectivity in a module and was the driving force behind the IoT-Ready Alliance that has now joined forces with Zhaga. (Photo credit: Image courtesy of Enlighted.)

The new standard designator for the intra-luminaire version of DALI is D4i. The organization has a new logo that will be carried by compliant products. And the organization will begin compliance and interoperability testing later this year. We’d expect companies such as Signify, Osram, and Tridonic to transition to the industry standard in their connected lighting platforms. Enlighted has also been an innovator in combining multiple sensors and connectivity into one compact module, albeit using proprietary connectivity (Fig. 4). But given its support of the IoT-Ready Alliance, we’d expect that company to support D4i going forward.

Mechanical and electrical

Still, the DiiA has not defined a mechanical or electrical standard for how a D4i module might connect to a luminaire. But such definitions have been the focus of the Zhaga Consortium, albeit for much different purposes — originally for interfaces to LED light engines. Zhaga, however, relaunched itself last year as the New Zhaga with a stated intent of developing IoT-centric standards.

Now Zhaga and the DiiA are working together. While the DiiA will control the actual signaling and protocol, Zhaga will specify the electrical connector and mechanical mounting of a D4i-compatible module on a luminaire. Zhaga has already published Book 18 that defines a connector and module footprint for outdoor luminaires such as street lights. The definition is smaller and more compact than the NEMA module used on top of street lights — originally developed for photocells. Zhaga modules will typically mount on the underside of a luminaire and potentially sense pedestrian or vehicular traffic. The organization is now working on Book 20 for indoor luminaires.

The Zhaga work, however, overlapped with the efforts of the IoT-Ready Alliance. Rather than work on competing standards, those two organizations decided to cooperate. More accurately, the IoT-Ready Alliance disbanded and suggested that its members join Zhaga to support that work.

Paths for all apps

It appears that the Zhaga and D4i standards will provide a path forward for luminaire manufacturers to support architectures with widely varying capabilities. It’s likely that Zhaga Book 20 will include the option of a sensor/communication module that connects to a driver via a 0–10V interface. Signify executive Robert Lee, who presented the aforementioned webcast, referred to such a configuration as “good” relative to the needs of commercial or industrial real estate. Such a luminaire design could meet regulatory requirements and qualify for rebates through market-transformation programs such as the DesignLights Consortium (DLC) in the US.

Moving to a design with a DALI-equipped driver that communicates with a sensor/connectivity module via D4i would qualify a luminaire for “better” or “best” descriptions, according to Lee. Those higher levels of praise equate to both subtle and substantial benefits. On the subtle side, Lee points out that luminaires will foreshadow their own failure through preventive maintenance routines that monitor operating temperature and hours of operation.

Somewhere in the middle you will find energy monitoring. Lee said it will become common for outdoor luminaires to integrate utility-grade meters that deliver accuracy to within ±2% of actual power usage and allow municipalities to pay exactly for the power they use. We’ve covered this concept in the past regarding IEEE Street and Area Lighting Conference presentations and the Georgia Power project that has long required its suppliers to equip street lights with a DALI-compatible driver.

The “best” designation will apply to the IoT applications that you have already heard about. The list would include office space utilization, indoor wayfinding, and more. Jónsson added more applications to the list in our recent webcast. For example, he said 3-D mapping of a space using lidar sensors could deliver better occupancy details and possibly detect concealed threats in a security application.

The key, however, is the ability for the SSL industry to move forward without paying the full price for the IoT upfront. And projects might need basic-level connectivity in some areas and bidirectional communications in others. It appears the industry has that path forward to support such flexibility.