DALI-2 DT6 vs DT8: When Tunable White Changes the Driver Selection

DALI is often described as one protocol, but inside a DALI-2 system the device types matter. The difference between DT6 and DT8 is the difference between a driver that dims a single white channel and one that coordinates two channels for tunable white. Choosing the wrong one means the lighting control system cannot speak to the driver, even though the DALI wires are connected correctly.

DALI-2 is the certification program built on the IEC 62386 standard family. DT6, defined in IEC 62386-207, is the standard dimmable control gear device type. A DT6 driver takes one DALI short address and controls one output channel. It dims from 0.1 percent to 100 percent, follows the standardized logarithmic dimming curve, and responds to scene and group commands. For general dimming of a fixed-color-temperature luminaire, DT6 is the default.

DT8, defined in IEC 62386-209, adds color control. A DT8 driver uses one address to coordinate multiple output channels, typically a warm-white channel and a cool-white channel for tunable white. The controller sends a color temperature command, and the driver internally splits the output between the two channels to produce the requested correlated color temperature. The same device type also supports RGB, RGBW, and xy color coordinates for color-changing luminaires. A DT8 driver can dim and tune from a single address, which is why it is preferred for human-centric lighting installations.

The selection rule is straightforward. If the luminaire has a fixed color temperature and only needs dimming, DT6 is sufficient and usually less expensive. If the luminaire is tunable white, warm-to-cool adjustable, or color-changing, the driver must be DT8. A DT6 driver cannot follow a color-temperature command, and a system that sends DT8 commands to a DT6 driver will either ignore them or dim only one channel, which produces a wrong-color result.

D4i is a further layer that sits on top of either device type. It adds per-driver energy reporting, fault diagnostics, and a 48 V bus power option so that control devices on the bus draw their power from the drivers rather than from a separate supply. D4i matters for facilities that want energy data back from the lighting system, for BMS integration, and for predictive maintenance. It is not a replacement for DT6 or DT8; it is an additional capability that the driver can carry.

For a waterproof constant-voltage driver sold into a market that is just starting to ask about smart lighting, the near-term demand is still DT6 dimming. The longer-term question is whether the product line needs a DT8 variant for tunable white strip installations. A 5-in-1 analog driver covers the retrofit and simple-dimming segment; a DALI-2 DT6 or DT8 driver covers the networked segment. Most manufacturers offer both and let the distributor choose based on the project rather than trying to cover everything with one part number.

A common commissioning mistake is addressing a DT8 driver as if it were DT6. A DT8 tunable-white driver has one short address but two output channels, and the controller has to send the DT8-specific color commands rather than the DT6 level command. If the installer addresses the driver and only sees one channel dim, the system is probably sending DT6 commands to a DT8 device. The fix is in the controller configuration, not the wiring, and it is worth checking the device type in the DALI commissioning software before blaming the driver.