By Paul Drosihn, General Manager, DALI Alliance
We’ve grown accustomed to the technology around us being wireless. It’s convenient to use and easy to install, requiring no cables. For many applications, wireless standards provide fast, reliable connectivity.
Wireless lighting control is an area that would benefit from further standardisation. Until recently, there has been lack of industry-standard protocols dedicated to wireless lighting control. The most widely used wireless protocols were not developed with lighting as the main focus, and lack the full range of specific capabilities that are needed for this application.
If lighting control features are needed, the best option to date has been to choose a wired protocol, such as the Digital Addressable Lighting Interface, or DALI. Developed specifically for lighting, DALI is based on the open global standard IEC 62386. It offers a comprehensive set of lighting-specific features, including dimming and colour control; sensing; emergency lighting; and the availability of luminaire, energy and diagnostics data.
Figure 1: DALI+ enables lighting control over wireless and IP-based networks
The DALI Alliance, which manages the DALI protocol, recently defined the new DALI+ specification. DALI+ enables existing DALI commands to be carried over wireless and IP-based networks instead of the dedicated pair of wires that are typically used to connect DALI devices. This enables the richness of DALI functionality to become available on wireless and IP-based networks. DALI+ is supported by a new specification called “Part 104 Changes and Additions”, which provides updates to the published Part 104 of the IEC 62386 standard.
As well as DALI+, a second approach has also been developed by the DALI Alliance. Here, standardised wireless-to-DALI gateways enable DALI lighting products to be integrated into non-DALI wireless ecosystems based on Bluetooth Mesh or Zigbee. With these two different approaches available, product developers and lighting designers can choose the best option for their application.
DALI+ uses the existing DALI language, with DALI commands packaged into IEC 62386 frames that are transported across wireless and IP-based carriers. Initially, DALI+ supports Thread as the carrier, which is an IP-based, low-power, wireless mesh networking protocol; see Figure 1. The DALI Alliance will consider adding DALI+ support for other carriers too in the future, such as Bluetooth Mesh, Ethernet (including Power over Ethernet, PoE) and Wi-Fi.
All DALI control gear and control devices can be implemented in DALI+, including LED drivers, colour-controllable drivers, emergency drivers, application controllers, push buttons and sensors. DALI+ systems retain the connectivity features of DALI wired systems; for instance, they can connect to a building management system (BMS) through a BACnet interface.
By supporting IP-based technology, DALI+ makes it easier for lighting control systems to communicate using existing IT systems and building automation services. For example, analytical data from lighting systems can be carried over a building’s existing network to a central computer or the cloud for analysis or archiving.
DALI+ with Thread
Thread uses the User Datagram Protocol (UDP) over 6LoWPAN, a low-power wireless protocol that enables IPv6 packets to be transmitted over networks based on IEEE 802.15.4 wireless technology. Thread is aimed at applications that only require low data rates, making it ideal as a carrier for DALI+ lighting control. Thread’s self-healing mesh network can scale up, and can become more resilient the larger it grows, providing dependable connectivity for lighting control. Reliable delivery can be achieved by using message acknowledgement to confirm delivery.
Security for DALI+ includes authentication and encryption methods that are already part of the carrier. All Thread communication is encrypted and authenticated using IEEE 802.15.4 security mechanisms, using AES with a 128-bit key. Only devices commissioned with the network key can exchange data, and a device-specific authentication secret is used to securely deliver the key to a device joining the network.
Connecting DALI+ and wired systems
In many systems, it may be desirable to use both DALI+ networks and existing wired DALI systems, enabled by bridges. The DALI commands and features are the same in both cases, and the application controllers in the DALI+ network communicate via a DALI+ bridge, which enables them to talk to all types of DALI wired control systems and devices; see Figure 2.
Figure 2: Bridges link wired and wireless DALI networks
A separate approach is to use a DALI+ application controller that can support multiple subnets; this could be any combination of DALI+ and wired DALI subnets. For example, Figure 3 shows a system with two DALI+ input devices (a sensor and a push button) connected wirelessly to a single application controller with a DALI+ interface. The application controller also has two interfaces for wired DALI systems, which contain luminaires and may optionally also include input devices.
The application controller receives event messages or polls the sensors and push buttons in both the wireless and wired systems. It then makes decisions and sends commands to the bus units in the wired DALI subnets, controlling the lighting.
Figure 3: Application controller with wireless and wired interfaces
For more complex systems, a backbone such as Ethernet can be used to connect multiple wireless DALI+ systems together. Figure 4 shows an example of such a complex system. In this example, there are two wireless Thread networks connected with an Ethernet cable via Thread border routers. A DALI+ bridge provides connectivity to two DALI wired buses (one of which is a D4i luminaire), and a multi-subnet application controller provides interfaces to two further wired subnets.
There are also non-DALI+ devices in the system in Figure 4, such as the door lock in the second Thread network. This example shows that the Thread network can also support other devices that are not controlled by DALI commands. The system in Figure 4 could be connected to a larger building-wide IP network, for example containing computers and other devices.
Figure 4: DALI+ system, with multiple Thread networks and wired devices
Putting it all into practice
DALI is a well-established, proven technology backed by a rigorous program for testing and certifying products, all managed by the DALI Alliance. This includes a centralised, online database of certified and registered products that is openly available to the industry and the public.
The newly-announced DALI+ specification (and DALI’s support for wireless gateways) builds on the proven capabilities and benefits of DALI, whilst maintaining the existing focus on certification and interoperability. The DALI Alliance is developing tests for DALI+ with Thread, which will be the first certification program for interoperable DALI+ devices; certified products and solutions are expected to be available soon.
With its support for wireless connectivity and IP-based networking, DALI+ creates new opportunities for lighting control systems, with more flexibility and simpler interfacing with IT and building management systems.
By enabling the development of wired, wireless and IP-based systems, in any combination, DALI+ increases choice, flexibility and creative freedom for lighting designers and specifiers. Whether it’s simple control of a few light fixtures or complicated, sensor-rich building-wide lighting networks, the new capabilities added to DALI provide a proven, reliable solution.