Even the most basic lighting controls can amplify the advantages of solid-state lighting by reducing energy consumption and enhancing the user experience. Smart, digital lighting control systems add a layer of sophistication, making full use of sensors as well as the data that can be retrieved from LED drivers. DALI—the Digital Addressable Lighting Interface—is a standardized lighting control technology that is built to enable smart, data-rich networks of connected lighting devices such as luminaires and sensors, each with its own address.
What is DALI?
Created more than two decades ago, DALI is a protocol or language that enables two-way digital communication and data exchange between lighting control devices. It provides a more sophisticated alternative to other control technologies such as 0-10V and Digital Signal Interface (DSI). Typically, DALI devices are connected by a dedicated pair of wires known as the DALI bus (wireless DALI is currently in an advanced stage of development). The DALI bus carries DALI power and data on the same pair of wires, often standard two-core cable; the polarity of the wires does not have to be observed. Each DALI network requires a bus power supply for the DALI communication signals. Some low-power devices, such as sensors, can be powered directly by the DALI bus in lieu of a dedicated power source.
Sensors detecting occupancy and light levels are an important source of information for the DALI system, as are other input devices such as switches, push buttons, and sliders. DALI sensors coupled with occupancy-based data analytics can provide a useful tool for facility managers tasked with reducing electricity consumption.
Photosensors also help save energy through daylight harvesting—telling the system how much natural light is available in a particular location and controlling the electric lighting in response. This technique also considers factors such as the time of day and the sun’s position in the sky. Some DALI systems can control both the lighting network and the window shades.
Sensor-based lighting control can optimize both the brightness and color temperature of electric lighting, creating a more comfortable environment for building occupants. Color control is one of many optional features enabled by DALI, which supports several standardized approaches, including tunable white.
Evolution and standardization
The DALI protocol has been deployed successfully in thousands of high-profile lighting projects worldwide, such as Beijing Daxing Airport, St. Peter’s Basilica in Vatican City, the Metro transit system in Doha, UAE, and a network of hundreds of thousands of outdoor lights operated by the utility Georgia Power in the U.S. DALI is based on the open international standard IEC 62386, published by the International Electrotechnical Commission. Early iterations of the standard covered only control gear. No procedure was in place to ensure that manufacturers were conforming to the device specifications.
This issue was addressed in two ways. First, the standard was restructured and expanded to cover specifications for all critical device types, including application controllers and sensors. Second, leading industry players in 2016 formed the DALI Alliance to create a certification program for interoperable DALI-based devices. Known as DALI‑2, this certification program is built on the latest version of the DALI protocol and is continually maintained and extended by the DALI Alliance.
Certification requires rigorous and comprehensive device testing, and the DALI Alliance verifies the test results before certification is granted. This strengthens market confidence in the interoperability of DALI-2 devices from different manufacturers. DALI-2 also includes backward compatibility with older-generation devices.
Intraluminaire networks and D4i
Lighting projects use DALI to connect multiple luminaires in wired networks that contain sensors and other devices. But DALI can also be used for small intraluminaire networks. Here, one or more LED drivers inside the luminaire are connected via a wired DALI bus to a DALI application controller and possibly to a separate sensor mounted outside the fixture.
In 2019, D4i certification was introduced for devices that have a feature set aligned with the requirements of intraluminaire networks. Along with supplying power to controllers or sensors in the intraluminaire network, D4i has a mandatory requirement for data. D4i LED drivers—and some DALI-2 drivers—are able to collect, store, and report a range of data relating to energy and power usage, maintenance and diagnostics, and luminaire information, such as its light output, CCT, and light distribution.
For example, in the Georgia Power project, luminaire information is programmed into a D4i LED driver in the factory. Once the D4i luminaire is installed and connected to the citywide network, the data it collects can be extracted into a user-supplied dashboard. This enables automated commissioning, saving thousands of person-hours; and remote asset management, allowing the utility to know the capabilities and status of all luminaires in its network.
Monitoring and reporting real-time power data are capabilities that can help optimize energy usage and supply the required performance information for code compliance or energy rebates. Meanwhile, the availability of operational and diagnostics data—run hours, temperature, and abnormal events such as under- or over-voltage conditions—can alert managers of faults through the system and allow facilities staff to deploy a predictive-maintenance strategy.
Network compatibility
DALI systems can be built to exchange information with external networks that use other communication protocols via interface devices, such as gateways, hubs, and routers. For example, DALI lighting networks are often incorporated into building management systems (BMS), which use protocols such as BACnet and KNX. These BMS networks control other building functions, such as HVAC.
Recently, the DALI Alliance standardized the interfaces between DALI systems and two wireless ecosystems: Bluetooth mesh and Zigbee. The two distinct specifications for these “wireless-to-DALI gateways” enable the use of existing wired DALI lighting products in non-DALI wireless network. Now a Bluetooth mesh network can control DALI luminaires that each have a gateway device; or the wireless network can control a subnet of DALI luminaires and sensors via a single gateway.
Flexibility and wireless connectivity
DALI is inherently flexible and lends itself to future-proof designs that also extend the useful life of a lighting control system. Changes to the design and operation of a DALI system can often be dealt with by software reprogramming, rather than by rewiring or replacing luminaires and other equipment. A building operator, for example, could change the utilization of space for new tenants by grouping devices and luminaires differently.
While wired systems provide network stability and reliable connectivity, interest is growing in wireless lighting control. Depending on the specific location, positioning wireless control devices without the restrictions of having to run network cables is possible (though they would still require a power supply). Going wireless can increase not only flexibility, but also the ability to scale up systems and add new devices. With no new cabling, labor and material costs are reduced, and the risk of damage to the building drops.
However, a wired solution can be preferred in certain scenarios; for example, where architectural features cause attenuation of the wireless signal. In other circumstances, hybrid solutions may be desirable. The DALI Alliance is providing choice and future flexibility by developing solutions that combine DALI with wireless connectivity. Separate from the standardized wireless-to-DALI gateways described earlier, the DALI Alliance is also developing true wireless DALI, which will reach the market as DALI+ later this year. DALI continues to evolve, addressing the connectivity and data requirements of the SSL market.
This article appeared in the Spring/Summer 2023 issue of Architectural SSL.
