Digital Addressable Lighting Interface

Protocol

International standard	IEC 62386, previously IEC 60929
Developed by	Digital Illumination Interface Alliance (Activity Group DALI before 2017)
Introduced	1990s
Industry	lighting

Connector

Type	lighting control
Superseded	[1-10 V/[0-10 V lighting control
General specifications
Hot pluggable	Yes
External	Yes
Cable	mains-rated, separate or part of power cable: check with local wiring regulations
Pins	2
Connector	1
Electrical
Signal	16 V DC (typical)
Max. voltage	22.5 V DC
Max. current	250 mA
Data
Width	16, 24 or 32 bits (forward), 8 bits (backward)
Bitrate	1200 bit/s
Protocol	asynchronous, half-duplex, serial protocol over a two-wire bus
Pinout
Pin 1	DA (or DA+)
Pin 2	DA (or DA-)

Digital Addressable Lighting Interface (DALI) is a trademark for network-based systems that control lighting in building automation. The underlying technology was established by a consortium of lighting equipment manufacturers as a successor for 1-10 V/0–10 V lighting control systems, and as an open standard alternative to several proprietary protocols.

DALI is specified by a series of technical standards in IEC 62386. Standards conformance ensures that equipment from different manufacturers will interoperate. The DALI trademark is allowed on devices that comply with the DiiA testing and certification requirements, and are listed as either registered (DALI version-1) or certified (DALI-2) on the DiiA website. D4i certification - an extension of DALI-2 - was added by DiiA in November 2019.

Members of the AG DALI were allowed to use the DALI trademark until the DALI working party was dissolved on 30 March 2017. Since 9 June 2017, Digital Illumination Interface Alliance (DiiA) certifies DALI products. DiiA is a Partner Program of IEEE-ISTO.

Technical overview

A DALI network consists of at least one application controller, input devices (e.g. sensors and push-buttons), bus power supplies (which may be built into any of the products), control gear (e.g., electrical ballasts, LED drivers and dimmers) that have DALI interfaces. Application controllers can control, configure or query each device by means of a bi-directional data exchange. The DALI protocol permits devices to be individually addressed and it also allows multiple devices to be addressed simultaneously via group and broadcast messages.DiiA - Introducing DALI

Each device is assigned a unique short address in the numeric range 0 to 63, making possible up to 64 control gear plus 64 control devices in a basic system. Address assignment is performed over the bus using a "commissioning" protocol, usually after all hardware is installed. Data is transferred between devices by means of an asynchronous, half-duplex, serial protocol over a two-wire bus, with a fixed data transfer rate of 1200 bit/s.

A single pair of wires comprise the bus used for communication to all devices on a DALI network. The network can be arranged in a bus or star topology, or a combination of these. Each device on a DALI network can be individually addressed, unlike DSI and 0–10V devices. Consequently, DALI networks use fewer wires than DSI or 0–10V systems.

The bus is used for both signal and power. A power supply provides up to 250 mA at typically 16 V DC; each device may draw up to 2 mA unless bus-powered. While many devices are line-powered, low-power devices such as motion detectors may be powered directly from the DALI bus. Each device has a bridge rectifier on its input so it is polarity-insensitive. The bus is a wired-AND configuration where signals are sent by briefly shorting the bus to a low voltage level. (The power supply is required to tolerate this, without supplying more than 250 mA.)

Although the DALI control cable operates at ELV potential, it is not classified as SELV (Safety Extra Low Voltage) and must be treated as if it has only basic insulation from mains. This has the disadvantage that the network cable is required to be mains-rated, but has the advantage that it may be run next to mains cables or within a multi-core cable which includes mains power. Also, mains-powered devices (e.g., LED drivers) need only provide functional insulation between the mains and the DALI control wires.

The network cable is required to provide a maximum drop of 2 volts along the cable. At 250 mA of supply current, that requires a resistance of ≤ 4 Ω per wire. This wire size needed to achieve this depends on the length of the bus, up to a maximum of 16 AWG (1.3 mm²) at 300 m when using the maximum rating of bus power supply.

The speed is kept low so no termination resistors are required, and data is transmitted using relatively high voltages (0±4.5 V for low and 16±6.5 V for high) enabling reliable communications in the presence of significant electrical noise. (This also allows plenty of headroom for a bridge rectifier in each slave.)

Each bit is sent Manchester coded (a "1" bit is low for the first half of the bit time, and high for the second, while "0" is the reverse), so that power is present for half of each bit time. When the bus is idle, it is high voltage all the time (which is not the same as a data bit). Frames begin with a "1" start bit, then 8 to 32 data bits in msbit-first order (standard RS-232 is lsbit-first), followed by a minimum of 2.45 ms of idle.

Device addressing

A DALI device, such as an LED driver, can be controlled individually via its short address. In addition to this method of control, DALI devices can be arranged into groups in which all devices of the same Group can interact with each other. For example, a room with 4 ballasts can be changed from off to on in three common ways:

Single device

Using the Short Address, e.g. sending the following DALI messages:

• DALI Short Address 1 go to 100%
• DALI Short Address 2 go to 100%
• DALI Short Address 3 go to 100%
• DALI Short Address 4 go to 100%

This method has the advantage of not relying on the limited number of scenes available in each ballast, or having programmed each ballast with the required group numbers and scene information. The fade time of the transition can be chosen on the fly. This method can have an undesirable side effect called "Mexican Wave" when a single large room such as an auditorium contains many ballasts, due to network latency of the comparatively slow 1200 baud rate of DALI. For example, a transition from all on to all off may result in a visible delay between the first and last ballasts switching off. This issue is normally not a problem in rooms with a smaller numbers of ballasts.

Device groups

Using the DALI Group previously defined for the ballasts in the room, e.g.:

• DALI Group address 1 go to 100%

This method has the advantage of being immune to the "Mexican Wave" effect as described above. This method has the disadvantage of requiring each ballast to be programmed with the required group numbers and scene information. The fade time can still be configured on the fly, if required.

Broadcast

Using the DALI Broadcast command, all control gear will change to that level, e.g.:

• DALI Broadcast go to 50%

Brightness control

DALI lighting levels are specified by an 8-bit value, where 0 means off, 1 means 0.1% of full brightness, 254 means full brightness, and other values are logarithmically interpolated between, giving a 2.77% increase per step. That is, a (non-zero) control byte x denotes a power level of 10^{3(x−254)/253}.

(A value of 255 is reserved for freezing the current lighting level without changing it.)

This is designed to match human eye sensitivity so that perceived brightness steps will have uniform brightness change, and to achieve a uniform brightness between units from different manufacturers.

Scenes

Devices store 16 programmable output levels as "scenes". A single broadcast command causes each device to change to the configured level, e.g. dim lights over the audience and bright lights over the stage. (A programmed output level of 255 causes a device not to respond to a given scene.)

A 17th "system failure" scene is triggered by a loss of power (sustained low level) on the DALI bus, to provide a safe fallback if control is lost.

Commands for control gear

Forward frames sent to control gear are 16 bits long, comprising an address byte followed by an opcode byte. The address byte specifies a target device or a special command addressed to all devices.

When addressing a device, the least significant bit of the address byte specifies the interpretation of the opcode byte, with "0" meaning a target (light) level byte follows, and "1" meaning a command follows.

Several important special commands are used to save the data byte to one of the three "data transfer registers" which can be used as a parameter by subsequent commands.

Address byte format:

• 0AAA AAAS: Target device 0 ≤ A < 64.
• 100A AAAS: Target group 0 ≤ A < 16. Each control gear may be a member of any or all groups.
• 1111 110S: Broadcast unaddressed
• 1111 111S: Broadcast
• 1010 0000 to 1100 1011: Special commands
• 1100 1100 to 1111 1011: Reserved

Common control gear commands:

Command	Description
Control commands
DAPC (level)	Sets targetLevel (0-255) using the current fade time, or stops a running fade (255).
OFF	Set targetLevel to 0 without fading
UP	Starts or continues a fade up for 200ms at the current fade rate
DOWN	Starts or continues a fade down for 200ms at the current fade rate
STEP UP	Increments targetLevel by 1 without fading
STEP DOWN	Decrements targetLevel by 1 without fading
RECALL MAX LEVEL	Set targetLevel to MAX level without fading
RECALL MIN LEVEL	Set targetLevel to MIN levelwithout fading
STEP DOWN AND OFF	Decrements targetLevel by 1 without fading, turning off if already at MIN level
ON AND STEP UP	Increments targetLevel by 1 without fading, turning on to MIN level if currently off
GO TO LAST ACTIVE LEVEL	Sets targetLevel to the last active (non-zero) level, using the current fade time.
GO TO SCENE (sceneNumber)	Sets targetLevel to the value stored in scene sceneNumber, using the current fade time, or no change if the value stored in the scene is 255.
Configuration commands
RESET	Changes all varables to their reset values.
STORE ACTUAL LEVEL IN DTR0	Stores the actualLevel (light output level) in register DTR0
IDENTIFY DEVICE	Starts a temporary identification process such as flashing the lamps, making a sound or transmitting an RF beacon.
SET MAX LEVEL (DTR0)	Changes maxLevel level to DTR0
SET MIN LEVEL (DTR0)	Changes minLevel level to DTR0
SET SYSTEM FAILURE LEVEL (DTR0)	Changes systemFailureLevel to DTR0
SET POWER ON LEVEL (DTR0)	Changes powerOnLevel to DTR0
SET FADE TIME (DTR0)	Changes fadeTime to DTR0
SET FADE RATE (DTR0)	Changes fadeRate to DTR0
SET EXTENDED FADE TIME (DTR0)	Changes the two 4-bit variables extendedFadeTimeMultiplier:extendedFadeTimeBase to DTR0
SET SCENE (DTR0, sceneX)	Changes sceneX to the value DTR0
ADD TO GROUP (group)	Adds the control gear into the specified group
Query commands
QUERY STATUS	Asks the control gear for the current status. Reply bits: 0=controlGearFailure; 1=lampFailure; 2=lampOn; 3=limitError; 4=fadeRunning; 5=resetState; 6=shortAddress is MASK; 7=powerCycleSeen
QUERY LAMP FAILURE	Asks the control gear if it is currently detecting a lamp failure.
QUERY ACTUAL LEVEL	Asks the control gear what the current actualLevel (output level) is.

Commands for control devices

The DALI-2 standard added standardisation of control devices. Control devices can include input devices such as daylight sensors, passive infrared room occupancy sensors, and manual lighting controls, or they can be application controllers that are the "branins" of the system - using information to make decisions and control the lights and other devices. Control devices can also combine the functionality of an application controller and an input device. Control devices use 24-bit forward frames, which are ignored by control gear, so up to 64 control devices may share the bus with up to 64 control gear.

DALI and Bluetooth

On 2017-02-16 the Mesh Professional Lighting Subgroup was created as a forum to discuss and develop Bluetooth mesh technology as a foundation for the wireless lighting standard.

See also

• Dimmer
• Lighting control console
• Lighting control system

External links

• Digital Illumination Interface Alliance