Digital Addressable Lighting Interface

A DALI network consists of at least one application controller and bus power supply (which may be built into any of the products) as well as input devices (e.g. sensors and push-buttons), control gear (e.g., electrical ballasts, LED drivers and dimmers) with DALI interfaces. Application controllers can control, configure or query each device by means of a bi-directional data exchange. The DALI protocol permits addressing devices individually, in groups or via broadcast. [2]

Each device is assigned a unique short address between 0 to 63, making up to 64 control gear devices and 64 control devices possible 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 comprises the bus used for communication on a DALI network. The network can be arranged in bus or star topology, or a combination of these. Each device on a DALI network can be addressed individually, unlike DSI and 0–10V devices. Consequently, DALI networks typically use fewer wires than DSI or 0–10V systems.

The bus is used for both signal and bus 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.[3]^:20,35 While many devices are mains-powered (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, limiting the current to 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.[3]^:19 At 250 mA of supply current, that requires a resistance of ≤ 4 Ω per wire. The wire size needed to achieve this depends on the length of the bus, up to a recommended maximum of 2.5 mm² at 300 m when using the maximum rating of bus power supply.

The speed is kept low so no termination resistors are required,[3]^:21 and data is transmitted using relatively high voltages (0±4.5 V for low and 16±6.5 V for high[3]^:19) 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 using Manchester encoding (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. When the bus is idle, the voltage level is continuously high (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.

A DALI device, such as an LED driver, can be controlled individually via its short address. Additionally, DALI devices may be arranged into groups in which all devices of the same group can respond to the commands addressed to the group. For example, a room with 4 ballasts can be changed from off to on in three common ways:

DALI lighting levels are specified by an 8-bit value, with 0 representing off, 1 means 0.1% of full brightness, 254 means full brightness, and other values being logarithmically interpolated, giving a 2.77% increase per step. I.e., 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 are uniform, and to ensure corresponding brightness levels in units from different manufacturers.[3]^:21

Devices store 16 programmable output levels as "scenes". A single broadcast command causes each device to change to its 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.

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:[4][5][6]

The DALI-2 standard [7] 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 "brains" 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.

DiiA published several new specifications in 2018 and 2019, extending DALI-2 functionality with power and data, especially for intra-luminaire DALI systems. Applications include indoor and outdoor luminaires, and small DALI systems. The D4i trademark is used on certified products to indicate that these new features are included in the products.

IEC 62386-209 describes colour control gear. This describes several colour types - methods of controlling colour. The most popular of these is Tc (tunable white), and was added to DALI-2 certification in January 2020.[8]

IEC 62386-202 describes self-contained emergency lighting. Features include automated triggering of function tests and duration tests, and recording of results. These devices are currently included in DALI version-1 registration, with tests for DALI-2 certification in development. Such DALI version-1 products can be mixed with DALI-2 products in the same system, with no problems expected.[9]

IEC 62386-104[10]describes several wireless and wired transport alternatives to the conventional wired DALI bus system.[11] DiiA is working with other industry associations to enable certification of DALI-2 products that operate over certain underlying wireless carriers. It is also possible to combine DALI with wireless communication via application gateways that translate between DALI and the wireless protocol of choice. While such gateways are not standardized, DiiA is working with other industry associations to develop the necessary specifications and tests to achieve this. DiiA: DALI and Wireless

• Dimmer
• Lighting control console
• Lighting control system

• Digital Illumination Interface Alliance