In commercial buildings, lighting electricity costs are easy to underestimate. The German Working Group on Energy Balances (Arbeitsgemeinschaft Energiebilanzen, AGEB) reports that lighting accounts for 13% of Germany's total electricity consumption, with commercial, industrial and other professional lighting making up about 85% of that share[4]. The German electrical trade estimates annual electricity costs for non-residential building lighting at around €12 billion across Germany. Even a 200 m² open-plan office can spend several thousand euros per year on lighting. Some of that cost is usually avoidable: luminaires left on after hours, circuits running at full output in daylight, or hidden overloads caused by poor power sizing.

A conventional DALI system controls when lights switch on and off and how they dim. But it does not automatically tell you how much power each luminaire actually draws, how long a driver has been operating, or whether a component is approaching a fault condition. D4i changes this by making every certified LED driver a data node that can report power, energy, asset and diagnostic information in a standardised way.

What D4i Is

D4i stands for “DALI for IoT” – it is an extended certification mark built on top of DALI-2. D4i is not a new communication protocol; it is a combination of three optional data specification sets defined in IEC 62386[1]:

• Part 251 (Luminaire Data): Asset information factory-encoded by the luminaire manufacturer – model, rated power, colour temperature, CRI, lumen output
• Part 252 (Energy Reporting): Real-time power, cumulative energy consumption, load-side power data[2]
• Part 253 (Diagnostics & Maintenance): Operating hours, start counter, failure flags; temperature monitoring is supported on some drivers (specific fields are optional depending on driver implementation)[3]

D4i-certified LED drivers keep normal DALI-2 control and add the three data functions above. The data is stored in a standard format inside the driver and can be read by the lighting control network when needed. No extra sensor or separate gateway is required; it uses the existing DALI bus.

Three Core Capabilities

Energy data acquisition

Each luminaire reports instantaneous power in watts and cumulative energy consumption in kWh. Property owners can read lighting energy at fixture level instead of estimating it from circuit loads or operating schedules.

Diagnostics and maintenance

Operating hours, start counter and failure flags are updated in the system. A management platform can use thresholds to warn about abnormal behaviour before a luminaire stops working. In our projects, that warning period is usually several weeks to a few months. Some D4i drivers also support driver temperature monitoring for over-temperature alerts.

Asset information storage

Model, rated power, colour temperature, CRI and lumen output are factory-encoded in the driver. During commissioning, the system can read this information and populate the asset register automatically. That reduces manual entry, documentation time and simple copy-paste errors.

The Value of Energy Data in Different Use Cases

Energy data is useful in different ways depending on the project.

Private residential users

For private homes, energy monitoring is mainly about seeing the actual power draw of each luminaire. If one luminaire stays above its rated value, the cause may be a driver fault or a hidden overload caused by ageing. That can be spotted before burnout or a cascading failure.

Property managers

For property managers, the same data supports monthly energy reports by season, floor or common area. Germany's Nebenkosten (operating cost) allocation rules require transparent documentation for communal lighting electricity. D4i makes per-zone and per-floor lighting energy accounting practical, which can reduce disputes between property managers and tenants over lighting cost allocation.

Electrical design

Electrical designers can also use the data. During commissioning, the system records the actual peak power of each DALI branch. This checks the original design assumptions and gives the design team real project data for the next installation.

Predictive Maintenance: Before the Light Fails

LED lifespan is often expressed as L70/B50: the point where light output has fallen to 70% of the initial value, or 50% of luminaires have failed. In many projects, maintenance is still based on rough lifespan estimates or on waiting until a lamp fails. D4i gives the system better data to plan replacements earlier.

IEC 62386-253[3] defines multiple diagnostic data fields for LED drivers and light sources. Three are most valuable for maintenance planning:

Operating hours

The driver records total on-time. Combined with the luminaire's rated lifespan, this allows the system to estimate remaining useful life. For example, a luminaire rated at L70@50,000 h that has run 42,000 h has about 16% of its rated lifespan remaining. The next replacement batch can then be planned before failures start.

Driver temperature

Overheating is one of the main failure modes for LED drivers. Some D4i drivers report internal temperature in real time and trigger an alert when a threshold is exceeded. In real projects, an early warning usually gives the maintenance team several weeks before component degradation speeds up.

Failure flags

Startup failure, output overcurrent and internal faults are encoded as standardised fault types in Part 253. When the system receives a failure flag, it can create a work order immediately instead of waiting for a tenant complaint.

Practical Application Scenarios

Scenario 1: Residential lighting management

In a single-family home, D4i is mainly useful for energy transparency. Take a 200 m² three-storey house with about 45 luminaires at 8 W each. A D4i dashboard can show power and monthly consumption by floor. With luminaire-level data, the homeowner can see if one circuit or luminaire is drawing much more than its rated power, often an early sign of a failing driver. The same dashboard tracks operating hours and flags luminaires that are nearing their rated lifespan.

Scenario 2: Multi-property portfolio management

A property management company might oversee 8 buildings, each with 20-40 luminaires, or roughly 240 units in total. Without D4i, many failures are only discovered after tenant complaints. With D4i, fault alerts arrive in real time and operating-hours data helps plan batch replacement. Instead of replacing after failure, the maintenance team can target the longest-running luminaires in the same batch. In our experience, this kind of batch planning can reduce emergency call-out costs by 30-40% compared with reactive maintenance.

Scenario 3: Small commercial space

A café or retail shop with fixed opening hours can use D4i energy reporting for a monthly consumption report by zone: window display lighting at 14 h/day, sales floor at 10 h/day and back-of-house at 6 h/day. The monthly figures give the owner a baseline for each zone. If the display zone draws 2 kWh more than usual in a given month, it is worth checking. For shops with shared Nebenkosten arrangements, per-zone data provides documentation for allocating communal lighting costs[5].

D4i vs Standard DALI – Feature Comparison

Future Direction: D4i, IoT, and Building Energy Management

D4i is part of a broader shift in lighting: from control only to control plus data. Three developments are especially relevant for planning:

D4i + BACnet / KNX

D4i data can be passed into Building Automation Systems (BAS) through gateways, so lighting energy becomes part of the building's wider energy management. IEC 62386-253 diagnostic data is already structured for this kind of integration.

D4i + BIM

Building Information Modelling (BIM) depends on accurate equipment lists during design and operation. D4i Part 251 asset data can be imported into BIM systems, reducing manual checks and making equipment replacements easier to audit later.

D4i + utility demand response

As the EU Energy Performance of Buildings Directive (EPBD) adds pressure for sub-metering in large commercial buildings, D4i's standardised energy reporting interface is a practical option for lighting sub-metering[5].

For homeowners planning a new build or renovation, D4i is not something for the distant future. It is already available on D4i-capable drivers and can be planned as an upgrade path for DALI installations.

FAQ

References

TILLUME Product Range

TILLUME covers the main layers of a modern DALI installation:

24V LED Power Supplies & DALI Drivers

TILLUME 24V DALI Power Supply & Driver Range – constant voltage LED drivers with DALI-2 control, designed for reliable power delivery and full DALI bus integration in both residential and commercial projects.

Expert Series – CRI90 LED Spot Modules

TILLUME Expert CRI90 LED Spot Series – high colour rendering (CRI ≥ 90) LED spot modules designed for residential and hospitality applications where accurate colour reproduction matters.

Master Series – CRI95 LED Spot Modules

TILLUME Master CRI95 LED Spot Series – CRI ≥ 95 LED spot modules for professional and commercial installations where colour fidelity is a specification requirement.

Article by Jarvis for TILLUME · 2026-05-06