What is DALI ?
DALI stands for Digital Addressable Lighting Interface. It is a 2-way communications protocol that is used to provide control over, and communication between, the components in a lighting system.
DALI originated in the late 1990s and was defined in IEC60929. Since then it has been substantially modified. The current (2020) version of DALI is called DALI-2 and this is defined in IEC62386.
The original DALI (version 1) logo and the newer DALI-2 logo.
Both logos are the property of DiiA. This is the Digital Illumination Interface Alliance, an open, global consortium of lighting companies that aims to grow the market for lighting-control solutions based on digital addressable lighting interface technology.
There is a very wide range of DALI enabled lighting control products available from all the leading manufacturers and it is now widely recognised to be the global standard for lighting control.
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 & 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.
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 lighting-specific functions.
ARE ALL DALI PRODUCTS COMPATIBLE WITH EACH OTHER?
With the original version of DALI there were some compatibility problems because the specification was quite limited in scope. Each DALI data frame was just 16-bits (8-bits for the address and 8-bits for the command), so the number of commands available was very limited and there was no collision detection. In consequence, several manufacturers tried to expand its capabilities by making their own additions, resulting in some incompatibilities.
With the advent of DALI-2 this has been overcome.
- DALI-2 is much more ambitious in its scope and contains many features that were not in the original version. The result of this is that the additions that individual manufacturers made to DALI are no longer relevant. For a more detailed description of the DALI-2 architecture, please go to “How does DALI work”, below.
- The DALI-2 logo is owned by DiiA (the Digital Illumination Interface Alliance) and they have attached strict conditions to its use. Chief amongst these is that no product can carry the DALI-2 logo unless it has undergone an independent certification process to check for full compliance with IEC62386.
DALI-2 allows for the use of both DALI-2 and DALI components in a single installation, subject to some restrictions. In practice, this means that DALI LED drivers (as the main example) can be used in a DALI-2 installation.
HOW DOES DALI COMPARE WITH KNX, LON and BACnet?
KNX, LON and BACnet are building control protocols, designed for integrating and controlling multiple devices and systems throughout a building. There are virtually no LED drivers available in the market that can support a direct connection to these protocols (though a very small number of LED drivers is available with a KNX interface) so they cannot be implemented as lighting control protocols.
In contrast, DALI and DALI-2 were designed specifically for lighting control and the DALI-2 command set contains many lighting-specific commands. These include commands and features for dimming, colour changing, scene-setting, emergency test and feedback and circadian lighting. There is a very wide range of lighting control components, especially LED drivers, that support a direct DALI connection.
In many implementations KNX, LON, BACnet and similar protocols would be used by a building management system (BMS) for overall building control (integrating HVAC, security, access control, lifts etc), while DALI would be used to control just the lighting. Where necessary, a gateway would provide intercommunication between the BMS and the lighting system so that, for example, all the corridor lighting could be switched on via DALI if an intruder was detected by the security system.
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.
- 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.
- Instances.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 3 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.
HOW IS DALI WIRED?
- What topology is used for DALI? DALI will work with bus, star (hub and spoke), tree or line topologies, or any combination of these.
- It will not work with any sort of ring or mesh wiring topology
- What is the DALI voltage? DALI operates at c16V. However, a DALI bus is not SELV. Therefore, it must always be wired in mains-rated cable or flex.
- Is DALI polarity sensitive? No, it is not. The pair of wires that form the DALI bus are not polarity sensitive. Terminals on DALI devices, such as LED drivers, are typically marked DA, DA.
- Does DALI wiring need to be shielded? No, it does not need to be shielded. The data rate is relatively slow (1,200 baud), the bus voltage is relatively high (16V) and there is a large tolerance of voltage fluctuation. Together, these factors make the bus very robust in the presence of electrical interference, so shielding is not required.
- What cable or flex is suitable for DALI? DALI is most commonly wired with a multi-core cable that also carries mains power. Typical cables would be either 5-core (live, earth, neutral, DA, DA) or 6-core (live, emergency live, earth, neutral, DA, DA).
6-core mains rated flex suitable for a DALI installation.
- What is a DALI driver? A DALI driver is an LED driver that will accept a DALI or DALI-2 input. In addition to its live & neutral terminals it will have two additional terminals marked DA, DA for attaching the DALI bus. The most modern DALI drivers carry the DALI-2 logo, indicating that they have been subjected to the certification process required by the current IEC standard.
- What is DALI control? DALI control refers to the technology used to control lighting. Other technologies exist, notably 0-10V and 1-10V, but DALI (and its latest version, DALI-2) is the globally accepted standard for commercial lighting control.
- How do you programme a DALI device? This varies from one manufacturer to another and will usually involve several steps. One of the first steps will always be to assign an address to each of the devices in the installation. Programming can be accomplished wirelessly with some manufacturers but other will require a wired connection to the DALI bus.