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.
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 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).