Tunable white lighting — luminaires that adjust colour temperature from warm white (2700K) to daylight (6500K) — is increasingly specified in healthcare, education, and corporate offices for circadian rhythm support and task-appropriate lighting. Zumtobel luminaires fitted with Tridonic DT8 DALI-2 drivers implement DALI Part 207 colour temperature control — the industry standard for tunable white over DALI. This guide covers DT8 driver programming, DALI Part 207 Tc mode commissioning, scene programming, circadian schedule setup, and KNX-DALI gateway integration.

DALI Part 207 and DT8 colour extension

DALI-2 Part 207 (Colour control) defines Device Type 8 (DT8) drivers with colour sub-types: (1) Tc (colour temperature): driver accepts DALI command SetColorTemperature (CT value 1000–20000 Mirek, where Mirek = 1000000/CCT_Kelvin). CCT 2700K = 370 Mirek, CCT 6500K = 154 Mirek. (2) XY (colour point on CIE1931 diagram): for RGBW/full colour. (3) RGBWAF: individual channel control. Zumtobel CRAFT LED luminaires with Tridonic LC 75W DALI-2 driver: DT8 Tc sub-type, CCT range 2700–6500K, dimming range 1–100%, minimum dim level 1% (no stroboscopic flicker per EN 61000-3-2). Tridonic LC 75W DALI-2 is IEC 62386 Part 201 + 207 certified — verify DALI-2 certification mark before ordering.

Helvar Router 950 or MDT DALI gateway for DT8

Helvar Router 950 supports DT8 colour temperature control natively — DALI commands SetColorTemperature transmitted alongside standard dim level commands. Helvar Imagine software (Windows): DALI line scan detects Tridonic DT8 devices, identifies colour capability. Group creation: Groups > New Group > select DT8 devices > name "Office Tunable White". Scene programming with DT8: Scenes > Scene 1 "Morning" > set group level 70% + colour temperature 4000K. Scene 2 "Presentation" > 90% + 5000K. Scene 3 "Relax" > 40% + 2700K. Scene 4 "Off" > 0%. KNX integration: Router 950 KNX module → scene recall via DPT 18.001 or direct colour temperature telegram (DPT 7.600, 16-bit unsigned, Mirek value). KNX GA for CCT: 1/2/0 (CCT setpoint, DPT 7.600). Sending 370 to GA 1/2/0 → 2700K.

MDT DALI Gateway DT8 commissioning in ETS6

MDT SCN-DALI.01 supports DT8 colour control via its ETS6 plug-in (version 3.x+). ETS6 plug-in: open plug-in > DALI scan > select DT8 devices in device list > confirm DT8 capability flag displayed. Group objects for DT8 colour: (1) Colour temperature (DPT 5.001, scaled 0–100% mapped to CCT min/max): ETS6 parameter CCT min = 2700K, max = 6500K. DPT 5.001 value 0% → 2700K, 100% → 6500K, 50% → ~4600K. (2) Absolute CCT (DPT 7.600, Mirek): direct Mirek value, more precise. (3) Scene recall (DPT 18.001): stores dim level AND colour temperature together in scene memory. ETS6 scene configuration: Group 1 scene 1 includes both dim level (80%) and CCT (4000K) for each DT8 device in the group — both stored simultaneously. DT8 scene advantage over KNX-only scene: DALI stores scene in driver memory — no KNX telegram needed during scene playback, only the scene recall DPT 18.001 telegram.

Circadian rhythm schedule programming

Circadian rhythm (human-centric lighting) schedule: adjust CCT throughout the day to match natural daylight cycle. Typical schedule: 07:00 = 2700K 50% (dawn warm light, gentle awakening). 09:00 = 4000K 75% (morning productive light). 12:00 = 5500K 90% (peak daylight, alertness). 14:00 = 5500K 85% (early afternoon sustained). 16:00 = 4000K 70% (afternoon transition). 18:00 = 3000K 50% (evening warm light). 21:00 = 2700K 30% (pre-sleep warm dim). Implementation in KNX: ETS6 time module (Gira X1 or MDT logic module) — add time entries for each schedule point → send CCT and dim level to respective DALI gateway GAs. For smooth interpolation (transition not step): advanced KNX logic modules (Loxone miniserver or IP-Symcon) send CCT values every 10 minutes as linear interpolation between schedule points — smooth 2700K→5500K transition over 2 hours. DALI controller integrates over time using last received CCT value.

Luminance measurement and daylight linking

Tunable white luminaires in perimeter zones (window-adjacent) benefit from DALI daylight controller (DT5) integration — automatic dimming based on daylight sensor. Helvar 397 DALI-2 sensor: daylight (lux), presence detection. Configuration in Imagine: Zone > Perimeter Office > add sensor 397 (DT5) > set target illuminance 500 lux (EN 12464-1 office task plane). When daylight rises → DALI controller dims tunable white luminaires to maintain 500 lux. CCT remains controlled independently by circadian schedule — only dim level is daylight-controlled. This is a two-layer control system: DALI DT5 controls intensity, KNX schedule controls CCT. The two control channels are independent — DT8 driver accepts both simultaneously.

Quality verification and flicker measurement

After commissioning: verify colour temperature accuracy with calibrated spectrometer (e.g., Konica Minolta CL-500A): measure CCT at DALI command 2700K, 4000K, 6500K — compare to target ±150K tolerance (Zumtobel CRAFT specification). Flicker measurement: IEC TR 61547-1 Pst < 1.0 at all dim levels — verify at 10%, 50%, 100% dim with DT8 active (flicker can increase at low dim levels with colour mixing). Log measurements in commissioning report: Luminaire ID, DALI address, measured CCT at 3 setpoints, Pst values. For BREEAM Hea 01 (visual comfort) credit: provide ILP lighting design report including tunable white specification, maintained illuminance (Em), colour rendering Ra ≥ 80, UGR < 19.