UP 255D21 KNX Brightness Sensor with Constant Light Level Controller 5WG1255-2DB21
This KNX ceiling brightness sensor delivers precise mixed light measurement with an integrated constant light level controller for automatic daylight-harvesting dimming — no separate controller needed. Mounted compactly, it measures ambient illuminance while driving one main luminaire group plus up to four additional groups at a user-defined lux setpoint. Daylight increases cause proportional dimming; decreases cause ramp-up — saving energy with visual comfort. Self-calibration ensures accuracy. IR decoder supports S 255/11 remote.
| Protocol | KNX TP, S-Mode ETS; mixed daylight + artificial light measurement |
| Mounting | Ceiling flush box min. Ø60 mm x 40 mm depth; surface adapter optional |
| Constant Light Controller | Integrated — main group + up to 4 additional groups |
| Control Mode | Fully automatic with self-calibration included |
| Switching Output | Integrated 2-point control (switching function) |
| Lux Setpoint | Configurable per group; different zone targets |
| Calibration | Automatic; no recalibration needed |
| IR Decoder | Integrated for S 255/11 remote |
| Programming Button | Front-accessible |
| Power Supply | Integrated bus coupler; DC 21–29 V KNX bus; no external power |
| Dimensions & Certification | 88x63x88 mm; IP20; Data sheet A6V10489482; Warranty 24 Months |
Offices with window walls, classrooms, open-plan workspaces, retail stores with glazed fronts, galleries where lighting must respond to daylight conditions. Pairs with KNX dimming actuators; 2-point output for non-dimmable on/off. Values broadcast for HVAC compensation or shading control.
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