DALI, an acronym for Digital Addressable Lighting Interface, is a communication protocol developed specifically for digital lighting control and enables the creation of robust, scalable and flexible systems. The main functions include switching luminaires on/off (individually or in groups), dimming and recalling lighting scenes.

Origins and evolution

DALI was originally developed by a group of leading lighting manufacturers as a standard interface to enable the digital control, configuration and interrogation of electronic ballasts for fluorescent tubes, replacing the traditional analogue 0-10 V or 1-10 V control.

First made public at the end of the 1990s, DALI has evolved and established itself as a standard protocol in the lighting industry in just a few years and was included in the international standard IEC 62386.

In this way, long-term compatibility between manufacturers was ensured and the standard became a guarantee for future developments. DALI-2 is the latest version of the protocol, which is geared towards greater functionality and interoperability of devices; to take this into account, IEC updated the standard in 2014.

System philosophy

Like KNX, it is a distributed intelligence system: each DALI device can exchange coded information via a standardised digital interface, a common communication protocol and a shared transmission medium (bus).

DALI is, however, a master/slave system, unlike KNX whose communication is typically peer-to-peer. In other words, in DALI the initiative for communication is assigned exclusively to the master device, while the slaves merely respond to the query received from the master.

Connectivity, topology and power supply

A two-wire cable (recommended 1.5 mm2, 15 AWG) is sufficient to power the electronics and data transmission; it is not necessary to respect the polarity of the wires (+/-), unlike systems with 0-10 V or 1-10 V control.

The maximum distance between two DALI devices is 300 m, and the system topology is free: linear and star connections can be combined, but looping must be avoided.

Each DALI system requires bus power that can be supplied by a dedicated device or by another device connected to the bus; when DALI is interfaced to KNX the power supply is provided by the KNX / DALI Gateway EK-BG1-TP that typically supplies 16 V (range: 9.5 V ... 22.5 V).

Addressing and Grouping

A single DALI bus system provides 64 addresses for ballasts and 64 addresses for controllers.

Like KNX, DALI devices can also be programmed to operate in groups. This offers great flexibility, as the lighting system can be reconfigured by simple software reprogramming, without the need for physical changes to the wiring.

The grouping of devices includes:

• 16 groups for ballasts; each device can be a member of any combination of the 16 groups;
• 32 groups for controllers; each device can be a member of any combination of the 32 groups;
• 32 groups for input device instances; each instance can be a member of up to 3 of these groups.

Commands and Scenarios

The different types of DALI commands allow control, configuration and interrogation of the various devices:

• Control commands: Turn lighting on or off, initiate fading at a certain brightness level or call up light scenes;
• Configuration commands: change the fade time or change the brightness level stored in a scene;
• Query commands: query the current brightness level or the presence of a lamp fault.

Commands can be addressed to individual devices, groups of devices or broadcast to all devices, making communication efficient.

Scenarios generally contain a brightness level; alternatively, they can be set to 'ignore'.

When a scene is recalled, the output is either set to the stored brightness level or has no effect if 'ignore' has been set.

Each ballast has 16 scenes. A single GO TO SCENE command instructs all luminaires or any combination of luminaires to go to the predefined brightness levels. References CEI EN 62386 Addressable digital lighting interface

Interfacing KNX and DALI Systems

The DALI system can be easily interfaced via a gateway to the KNX system - which performs the many complex building automation functions in a coordinated manner - becoming a sub-system specifically dedicated to the lighting function.

The digital nature of DALI allows two-way communication between devices, so that any DALI device can indicate a fault or respond to a query about its status: status feedback, for example, can signal a faulty lamp and be transmitted to KNX supervision via the KNX/DALI gateway.

Gateway DALI: