A modern building expects far more from its lighting installation than switching circuits on and off. The DALI-2 protocol answers that need: it turns individual luminaires into addressable network devices that accept dimming commands and, at the same time, report energy consumption, temperature and faults. For an IoT integrator it is the shortest path from a luminaire to telemetry in the cloud.
In short: DALI-2 is the second edition of the IEC 62386 standard — a digital two-wire bus running at 1200 bit/s that supports up to 64 addressable luminaires and 64 control devices per line, with certified support for sensors and multi-master operation, which the original DALI lacked.
What is the DALI-2 protocol?
DALI-2 is a digital lighting control interface described in the second edition of IEC 62386 and maintained and certified by DiiA, the Digital Illumination Interface Alliance. The acronym DALI stands for Digital Addressable Lighting Interface.
The key difference from the first version lies in the scope of certification. DALI-1 covered only the drivers powering luminaires (control gear, parts 2xx). DALI-2 also covers control devices (parts 3xx): occupancy sensors, light level sensors and push-button panels.
- Multi-master operation — several application controllers coexist on one line instead of a single master controller.
- Extended addressing — 64 luminaire addresses plus 64 control device addresses per segment.
- Formal conformance testing — products pass the DiiA programme and enter a public database of certified devices.
- Real interoperability — the interpretation gaps that made equipment from different vendors incompatible under DALI-1 have been closed.
How does the DALI-2 bus work?
The DALI-2 bus is a pair of wires with no defined polarity, and it may be routed in the same cable as mains power, for example in a 5 x 1.5 mm² cable. The nominal line voltage is 16 V DC and the bus power supply delivers a maximum of 250 mA.
Transmission runs at 1200 bit/s using Manchester encoding. A frame addressed to a luminaire is 19 bits long (address and command), the reply 9 bits. Maximum line length is around 300 m for a 1.5 mm² cross-section, with an allowed voltage drop of 2 V.
Dimming works in 254 steps along a logarithmic curve matched to the response of the human eye, covering 0.1% to 100% of luminous flux. The standard also defines 16 groups and 16 scenes per line, so an entire zone can be changed with a single broadcast command.
What do D4i and DALI+ add in IoT installations?
D4i is a certification that extends the DALI-2 protocol with standardised data collected inside the luminaire. Part 252 of the standard describes energy reporting, part 253 diagnostics and maintenance. In practice the controller reads energy consumption in watt-hours, active power, operating hours, the number of switching cycles and temperature directly from the driver.
DALI+ (part 104) moves the same application layer onto wireless media and IP networks, most often onto Thread. The luminaire logically remains a DALI device but physically communicates in a mesh network — which removes the need to pull a bus through refurbished buildings. We described the context of this family of standards in the article on Matter and Thread interoperability.
When should you use DALI-2 instead of KNX, BACnet or 0-10 V?
DALI-2 is a luminaire-layer protocol, not a whole-building protocol — that is the most important selection rule. The choice is not about replacing one standard with another, but about placing them correctly in layers.
- 0-10 V and 1-10 V — analogue control, no addressing and no feedback. Cheap, but completely blind in diagnostic terms.
- KNX — a building automation bus covering blinds, HVAC and scenes; lighting is usually attached to it through a KNX/DALI gateway.
- BACnet — the management layer (BMS) that aggregates data from subsystems, including DALI lines.
- DALI-2 — precise control and diagnostics of an individual luminaire, plus emergency lighting with self-testing according to part 202.
In a well-designed installation the layers complement each other: DALI-2 operates at floor level, while BACnet or MQTT operates across the whole facility.
How do you build a DALI-2 to MQTT gateway?
A DALI-2 gateway is an application controller that translates bus frames into network messages and back. A proven architecture for such a device splits into four layers.
- Physical layer — a galvanically isolated DALI transceiver and a microcontroller (ESP32-S3 or STM32) handling Manchester encoding, collision detection and line voltage measurement.
- Logic layer — commissioning, address map, groups, scenes and schedules stored in non-volatile memory so the lighting keeps working even when the uplink is down.
- Communication layer — MQTT with QoS 1, topics structured as building/floor/line/address, and a Last Will message for immediate detection of a lost gateway.
- Cloud layer — energy telemetry, fault alarms and test reports; we collected the design principles for this layer in our text on IoT gateway architecture.
Powering the controller and its peripherals is best solved with Power over Ethernet, which cuts the number of separate power supplies in the floor cabinet and simplifies backup power.
Which mistakes most often ruin DALI-2 deployments?
Most problems in DALI-2 installations come not from the protocol but from the electrical design and the commissioning process. Four causes recur most often.
- Exceeded current budget — the total device draw goes beyond the 250 mA of the bus power supply, which shows up as random transmission errors.
- An overly long line — a voltage drop above 2 V means the most distant luminaires stop responding at full load.
- No address documentation — years later nobody knows which address belongs to which luminaire, and re-commissioning wipes the scenes.
- Equipment without DiiA certification — a claim of DALI compatibility is not the same as certification and is a frequent source of subtle incompatibilities.
Frequently asked questions (FAQ)
Will DALI-1 devices work on a DALI-2 bus?
Yes, in most cases. A DALI-2 controller can drive older control gear compliant with the first edition of IEC 62386, because the physical layer and the basic command set have not changed. It does not work the other way round, however: DALI-2 sensors and push-buttons require a controller that supports part 103 of the standard.
How many luminaires can a single DALI-2 line handle?
One line addresses a maximum of 64 control gear units plus another 64 control devices. The practical limit, however, is the current budget: the bus power supply delivers up to 250 mA and each device typically draws 2–10 mA. Larger installations are split into several lines tied together by an application controller.
Is the DALI-2 protocol suitable for emergency lighting?
Yes — part 202 of IEC 62386 defines emergency luminaires with a self-test function. The controller triggers a functional test and a duration test, then reads the result and the battery status. Reports can be archived automatically, which considerably simplifies the documentation required by fire safety regulations.
Summary — key takeaways
The DALI-2 protocol delivers what no analogue control can offer: an address, feedback and data. D4i certification adds standardised energy telemetry and diagnostics, while DALI+ opens the way to wireless installations. Combined with an MQTT gateway, lighting becomes a fully fledged data source for maintenance systems and energy reporting.
At FSS Technology we design such systems from the hardware, firmware and cloud side alike — from the gateway PCB, through the communication stack, to analytics dashboards. If you are planning to integrate lighting with a supervisory system, see our connected device services and the scope of the system integrations we deliver.