DALI-2 Explained: DT6, DT8, and the Digital Control Bus Behind Modern Lighting

DALI — the Digital Addressable Lighting Interface — is the standard control protocol for modern commercial lighting, defined by the IEC 62386 series of standards. DALI-2 is the current version, released in its final form in 2017 after years of compatibility testing, and it is now the default protocol for dimmable lighting in offices, hotels, retail spaces, and industrial buildings. For anyone involved in the lighting supply chain, DALI-2 is worth understanding even when selling non-dimmable products, because it defines what 'smart lighting' means in the commercial world and why dimmable drivers are priced and specified the way they are.

The DALI bus is simple by design. Two wires — the DALI bus pair — connect all the control gear and controllers in a single network. The bus carries both power and data: the bus voltage is approximately 16V DC, with current limited to about 250mA, so the wiring does not require mains-rated isolation and can be run in ordinary cable. Each device on the bus has a unique short address, up to 64 devices per network, and devices are organized into groups (up to 16) and scenes (up to 16). Communication is bidirectional — the controller sends commands to the drivers, and the drivers report back their status and lamp failure conditions. This feedback capability is a major advance over analog control: the system knows when a lamp has failed, and the controller can report it instead of the facility manager discovering it by walking the building at night.

The protocol distinguishes between two categories of device: control devices (sensors, switches, controllers, gateways) and control gear (the drivers). DALI-2 added rigorous certification requirements for both, addressing the compatibility problems of the original DALI. Under DALI-2, every certified device is tested for interoperability with other certified devices, which is why a DALI-2 driver from one manufacturer works with a DALI-2 controller from another — the certification is the guarantee. The certification is administered by the DALI Alliance, and certified products carry the DALI-2 trademark with the device type indicated.

Within DALI-2, the device type determines what the driver can do. The two most important are DT6 and DT8. A DT6 driver is a single-channel device: it controls brightness on one channel, from 0.1 percent (the minimum dimming level that DALI-2 requires for smooth low-level control) to 100 percent, with a logarithmic dimming curve that matches the way the human eye perceives brightness. A DT8 driver is a multi-channel device: it controls tunable white (color temperature), RGB, or full color mixing, with all channels addressed through a single short address. The practical difference is simple: DT6 does brightness, DT8 does color. A project that needs tunable white — offices with human-centric lighting, retail with different color temperatures by season — specifies DT8; a project that only needs dimming specifies DT6, which is simpler and less expensive.

DALI-2 sits alongside other control methods, and each has its place. 0-10V analog dimming is older, simpler, and less expensive per device, but it is one-directional, has no feedback, and requires a separate control wire per channel. Leading-edge (triac) dimming is the retrofit solution for residential dimmer switches, with the compatibility limitations discussed elsewhere. Wireless protocols — Zigbee, Bluetooth, Wi-Fi — remove the control wiring entirely, at the cost of commissioning complexity and potential interference. DALI-2's advantage is a wired, deterministic, certified control bus that works identically across manufacturers and does not depend on radio environments.

For a buyer of constant voltage, non-dimmable drivers, the DALI-2 ecosystem matters in one practical way: it defines the market boundary. Non-dimmable drivers serve the large share of installations that do not need dimming — warehouses, signage, corridors, industrial lighting — where DALI-2 adds cost without adding value. Understanding the protocol helps the buyer explain to a customer why a non-dimmable product is the right choice for their application, and helps position the non-dimmable range against the dimmable range. The two products serve different projects; knowing the difference is a sales advantage, not a limitation.