SPECIAL FEATURE
SMART LIGHTING & LIGHTING CONTROL
SPOTLIGHT ON DALI With the market for smart lighting and connected controls projected to continue to grow for the foreseeable future, Mike Collins, Sales Director at Ovia – part of the Scolmore Group of companies – answers some questions on the DALI protocol, described as the largest wired digital open protocol in the world for lighting.
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ccording to Pål Karlsen, a research analyst for building technology with consultancy firm, Omdia, the market for smart lighting and connected controls is growing at a good speed and will continue to do so in the foreseeable future. Looking ahead, he forecasts that open protocols such as DALI, Zigbee and Bluetooth will be the growth winners over the next few years in smart lighting and connected controls. He believes that future-proofing and a clear business case will help reduce the risk of investment in smart lighting technologies. One of the approaches to future-proofing is to choose popular, open protocols with an ecosystem surrounding the technology, as a way of assuring the availability of substitute suppliers. Compared with analogue controls, ‘smart’ requirements like colour-temperature tuning, individual fixture control and integration with various sensors has made digital controls, such as DALI-2, a necessity.
The origins of DALI Originating in the late 1990’s, DALI (Digital Addressable Lighting Interface) is a bi-directional communications protocol that is used to provide control over, and communication between, the components in a lighting system.
DALI is a bi-directional communications protocol
Key features of DALI • It is an open protocol – any manufacturer can use it. • With DALI-2, interoperability between manufacturers is guaranteed by mandatory certification procedures. • Installation is simple. Power and control lines can be laid together and no shielding is required. • The wiring topology can be in the form of a star (hub and spoke), a tree or a line, or any combination of these. • Communication is digital, not analogue, so the exact same dimming values can be received by multiple devices, resulting in very stable and precise dimming performance.
• All devices have their own unique address in the system, opening a very wide range of possibilities for flexible control. This also allows all devices to be individually monitored and maintained.
How does DALI compare with 1-10V? DALI, like 1-10V, was designed for and by the lighting industry. Lighting control components, such as LED drivers and sensors, are available from a range of manufacturers that have DALI and 1-10V interfaces. However, that’s where the similarity ends. The main differences between DALI and 1-10V are: • DALI is addressable. This opens the way for many valuable features such as grouping, scene-setting and dynamic control, such as changing which sensors and switches control which light fittings in response to office layout changes. • DALI is digital, not analogue. This means that DALI can offer much more precise light level control and more consistent dimming. • DALI is a standard, so, for example, the dimming curve is standardised, meaning that equipment is interoperable between manufacturers. The 1-10V dimming curve has never been standardised, so using different brands of drivers on the same dimming channel could produce some very inconsistent results. • 1-10V can only control switching on/off and simple dimming. DALI can manage colour control, colour changing, emergency lighting testing and feedback, complex scene-setting and many other lightingspecific functions.
How does DALI work? The core of DALI is a bus – a pair of wires that carries digital control signals from input devices (such as sensors) to an application controller. The application controller applies the rules with which it has been programmed to generate outgoing signals to devices such as LED drivers.
• Bus power supply unit (PSU). This component is always required. It maintains the bus voltage at the required level. • Led fittings. All light fittings in a DALI installation require a DALI driver. A DALI driver can accept DALI commands directly from the DALI bus and respond accordingly. The drivers can be DALI or DALI-2 devices, but if they are not DALI-2 they will not have any of the new features introduced with this latest version, such as querying control gear failure, resending failed commands, or identifying devices. • Input devices – sensors, switches etc. These communicate with the application controller using 24-bit data frames. They do not communicate directly with the control devices (DALI 2 only). • I nstances. Often, a device such as a sensor will contain a number of separate devices within it. For example, sensors often include a movement detector (PIR), a light-level detector and an infra-red receiver. These are called instances – the single device has three instances. With DALI-2, each instance can belong to a different control group and each can be addressed to control different lighting groups. • Control devices – application controller. The application controller is the ‘brains’ of the system. It receives 24-bit messages from the sensors (etc.) and issues 16-bit commands to the control gear. The application controller also manages the data traffic on the DALI bus, checking for collisions and re-issuing commands as necessary. As a business, Ovia is continually developing products that incorporate the latest technology and its list of fittings that are compatible with the DALI protocol continues to be expanded. The company recently introduced a DALI signal converter which will transform 0-10V/ PWM dimmable light fittings, such as Ovia’s Hion and Grus highbays, to DALI dimmable light fittings. Ovia, oviauk.com
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