- DALI-2 (IEC 62386) is a wired communication protocol for dimming and status commands. DALI-2 certification means type-tested interoperability — not all “DALI-compatible” equipment is certified.
- Zhaga Book 18 defines the physical interface (the connector) between luminaire and OLC node. It enables replacement of the control node without opening the luminaire — but does not guarantee protocol compatibility across manufacturers.
- D4i (IEC 62386-253) adds a data layer: operating hours, energy metering, start counter, and fault flags. It is the basis for predictive maintenance rather than reactive.
- Wireless alternatives (Zigbee, LoRa, proprietary protocols) solve the cable problem but introduce RF requirements, gateway dependencies, and support questions that should be raised at procurement.
Three Standards — Three Different Things
It is common to see “DALI”, “Zhaga”, and “D4i” used almost synonymously in marketing text. They are, however, fundamentally distinct:
| Standard | Defines | Reference |
|---|---|---|
| DALI-2 | Communication protocol (2-wire, half-duplex). Dimming/control commands, status queries, addressing. Certification and type-testing requirements. | IEC 62386 (multiple parts) |
| Zhaga Book 18 | Physical interface: the connector and pin layout on the OLC node (Outdoor Luminaire Controller). The luminaire's mechanical and electrical connection to the control node. | Zhaga Book 18 (2021) |
| D4i | DALI sub-standards for luminaires: Part 251 (energy metering), Part 252 (diagnostics), Part 253 (data for light source). Collectively called D4i (“DALI for Luminaires”). | IEC 62386-251/252/253 |
A luminaire can have a Zhaga Book 18 connector without having a DALI-2-certified driver. A luminaire can have a DALI-2-certified driver without supporting the D4i data sub-standards. And a luminaire can support all three — which is the combination that delivers full functionality in a modern smart lighting system.
DALI-2 — The Protocol That Controls
DALI (Digital Addressable Lighting Interface) is a two-wire, half-duplex communication protocol for lighting control. It handles dimming, on/off commands, group addressing, and status queries on a shared bus with up to 64 addressable devices per segment.
DALI 1 was the original version. DALI-2 (introduced in 2014 and continuously revised) differs in one principally important way: certification requirements. A DALI-2 device has undergone type-testing against the standard — carried out by independent test institutes. The result is that devices from different manufacturers, both bearing the DALI-2 mark, should operate on the same bus. Without certification, interoperability is not guaranteed even if the manufacturer claims “DALI-compatible”.
What DALI-2 Handles — and Does Not Handle
DALI-2 is a local bus communication system. It handles:
- Dimming (0–100 % relative, with configurable curve)
- On/off commands and scene recall
- Group addressing (up to 16 groups per segment)
- Status queries: lamp failure, power supply failure, temperature warning
- Time schedules via DALI controller (not built into the protocol itself, but into the controller)
DALI-2 does not handle:
- Energy metering and operating hours at luminaire level — this requires D4i Part 251
- Wireless communication — DALI is a cable protocol
- Direct IP communication — a gateway is required to bridge DALI to the network
Zhaga Book 18 — The Connector That Enables Replacement
Zhaga is a consortium that standardises mechanical and electrical interfaces for LED lighting components. Book 18 specifically defines the interface between an outdoor luminaire and an OLC node (Outdoor Luminaire Controller) — that is, the external control unit mounted on the luminaire.
The Book 18 connector standardises:
- Connector mechanics and pin layout
- Supply voltage from luminaire to node (typically 5 V DC)
- DALI-2 signals from the luminaire to the node (luminaire DALI address)
- Neutral potential
What this enables: An OLC node with a Book 18 connector can be mounted and removed without opening the luminaire. This means the municipality can change controls supplier, upgrade to a new radio standard, or add sensors without replacing the luminaire.
Note: Zhaga ≠ Full Interoperability
Book 18 standardises the physical connector — but the protocol the OLC node uses over that connector can be Zigbee, LoRa, NB-IoT, WiFi, or a proprietary protocol. Two Zhaga-certified nodes from different manufacturers share the connector form but may communicate with entirely different platforms. Always check which central management system (CMS) the node belongs to — not just that it has a Book 18 connector.
D4i — Data for Predictive Maintenance
D4i (“DALI for luminaires”) is a collective term for three DALI sub-standards that add a data layer on top of the DALI-2 protocol:
| D4i Part | IEC Reference | Provides |
|---|---|---|
| Part 251 | IEC 62386-251 | Active and reactive energy at luminaire level (kWh, kVArh). Basis for actual energy metering and optimisation. |
| Part 252 | IEC 62386-252 | Diagnostic data: operating hours, driver temperature, start count, active fault flags (lamp failure, voltage fault). Foundation for predictive maintenance. |
| Part 253 | IEC 62386-253 | LED-specific data: remaining luminous flux (relative CLO reference), CRI, CCT. Enables automatic CLO (Constant Light Output) and lumen-based regulation. |
D4i makes it possible to shift maintenance from reactive (“replace when broken”) to predictive (“replace when operating hours and fault flags indicate increasing risk”). This is directly linked to the field failure mode hierarchy — see MTBF is not Lifespan. Operating hours and start counters from Part 252 give early indications that the driver is approaching its expected wear threshold.
Wireless Alternatives
When cable infrastructure is absent or too costly, wireless communication is an option. Common protocols in street lighting:
- Zigbee (IEEE 802.15.4) — mesh network with low power consumption. Requires a gateway to internet/CMS. Relatively short range per node (~100 m line-of-sight, better in mesh).
- LoRa / LoRaWAN — long range, low bandwidth. Suited to large geographic dispersal where Zigbee mesh does not reach. Depends on LoRaWAN coverage.
- NB-IoT — mobile-based (4G/5G network). No local gateway, but subscription-dependent.
- Proprietary protocols — common from system vendors. Lock-in risk if not documented and open.
The SMC housing is dielectric — it transmits radio signals. In a metal enclosure, wireless communication requires an external RF node mounted outside the housing. See SMC, Aluminium and Cast Iron — Material Selection for background on RF transparency.
Five Questions to Ask About Controls in Procurement
- DALI-2 certification: Has the driver been type-tested and certified by an independent test institute per IEC 62386? Or is it “compatible” without certification?
- D4i implementation: Which of Part 251, 252, and 253 are supported? Part 252 (diagnostics) carries the greatest value for maintenance strategy.
- Zhaga Book 18: Is the connector standardised? If the node is replaced — must the luminaire be opened?
- Platform dependency: If a wireless node is included — which CMS platform is it tied to? What happens to the data if the supplier ceases?
- Data rights: Who owns the collected operational data — the municipality or the system supplier?
VALDUR — Technical Note
VALDUR is supplied with a Tridonic Xitanium driver with DALI-2 certification and D4i support (Parts 251–253). The luminaire has a Zhaga Book 18 connector, enabling OLC node mounting without opening the luminaire. The wireless option AirGlow (Tridonic) can be mounted inside the luminaire and leverages the SMC housing's RF transparency without an external antenna. Further details on specific control options are available at POLAB Controls.
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How D4i diagnostics connect to real failure hierarchy and predictive maintenance
SMC, Aluminium and Cast Iron
Why RF transparency matters for wireless controls
What Don't We Know? — Open Questions
Are we dimming too much at night? The safe threshold for nocturnal dimming
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Sources
- IEC. (2018). IEC 62386-207:2018: Digital Addressable Lighting Interface — Part 207: Particular requirements for control gear — LED light sources (device type 8). (DALI-2 for LED drivers.)
- IEC. (2021). IEC 62386-251, -252, -253: DALI for Luminaires (D4i). (Energy metering, diagnostics and LED data.)
- Zhaga Consortium. (2021). Zhaga Book 18: Outdoor Luminaire Controller (OLC) Interface. (Mechanical and electrical interface for OLC node.)
- DALI Alliance. (2023). DALI-2 Certification Programme — Overview. DALI Alliance. (Certification requirements and interoperability.)
- IEC. (2015). EN 13201-5:2015: Road Lighting — Part 5: Energy Performance Indicators. (Energy metering in road lighting.)
- Tridonic. (2024). Xitanium DALI-2/D4i — Technical Product Documentation. Tridonic GmbH. (VALDUR driver, DALI-2 and D4i implementation.)