Controlling light in a large office: groups and DALI

In an office with hundreds of fittings, switches become a problem. The logic of lighting groups, what DALI can do and what to watch for in a project.

In a small office, lighting runs off two or three switches and nobody sees a problem. As the floor grows, things change: open-plan areas, meeting rooms, corridors, reception, archive. Everyone wants different light in their zone, someone leaves the whole floor on in the evening, and every layout change means an electrician opening the ceiling to rewire. Centralised control was designed for exactly this situation.

Starting with switched groups

The simplest approach is to divide fittings into physical groups, each fed by its own circuit and switch: the row by the windows is one group, the back of the room another, the corridor a third. It is cheap and easy to understand, but it has two weaknesses. First, groups are fixed by the wiring, so changing them after a layout change requires installation work. Second, lights can only be switched on and off; brightness cannot be adjusted.

For dimming, the 1–10 V analogue interface was used for many years. Two extra thin wires run to the driver, and the voltage level sets the brightness. It works, but every dimmed group still needs its own control line, and there is no feedback about the state of the fittings.

What DALI is

DALI (Digital Addressable Lighting Interface) is a digital protocol for lighting control defined in the international standard IEC 62386. The core idea is simple: each driver has its own address, and control commands travel over a shared two-wire bus. Which fitting belongs to which group is determined by software, not by cabling.

In practice this brings several possibilities:

• up to 64 devices can be addressed individually on one DALI line;
• each device can belong to several groups, with 16 groups defined in the standard;
• preset brightness scenes can be stored in each device;
• the system can query drivers for their status, for example a failed lamp.

The bus uses two wires and is not polarity sensitive, so swapping the wires does not disable the system. It is powered by a dedicated DALI bus power supply whose current is limited by the standard.

The updated version of the standard is called DALI-2. It also covers control devices such as sensors and push-button panels, and includes certification of interoperability between manufacturers. In a mixed-brand project, checking for DALI-2 certification reduces the risk of compatibility problems later.

Real scenarios in an office

The benefits show up in everyday work. In a meeting room, a "presentation" button dims the lights near the screen while keeping the rest on. In an open office, the window row is linked to a daylight sensor and dims automatically on sunny days. In corridors and toilets, motion sensors keep full light only when someone is there. At a set time in the evening, the building switches to night mode and forgotten lights go off.

When the layout changes — say an open area is split between two departments — groups are reassigned in software without touching the ceiling. Over the long life of a building, that is the biggest advantage.

What to watch for in the design

A DALI system is only convenient if it is planned properly. Some practical points:

• confirm DALI-compatible drivers when ordering fittings, because "converting" a panel with a standard driver later means replacing the driver;
• bus wires are often run in the same cable as the mains supply, but then the insulation must be rated for mains voltage;
• follow the manufacturer's guidance on line length and conductor size, as voltage drop causes problems on long runs;
• document the addressing and group table: which address is which fitting and where it is located;
• test every scene with the staff who will use it before handover.

The most common problem is the "undocumented system". If nobody knows how to change groups once the installer has left, a flexible system turns into a rigid and puzzling one.

Does every office need DALI?

Not always. In an office with a handful of rooms, well-planned switched groups and local motion sensors may be enough. DALI pays off in large buildings with frequently changing layouts, zones with different functions and a serious approach to energy management. Where a building management system (BMS) or KNX is already present, DALI connects to it through a gateway.

In a refurbishment where the ceiling cannot be opened, wireless control systems are another option. They allow fittings to be grouped without running a new bus, but network stability, device firmware updates and who holds access rights all need thinking through in advance. Whatever the technology, emergency lighting is subject to its own requirements, and ordinary control scenes must never be able to switch it off.

The Zəfər İşığı products that Zaferoğlu Elektrik manufactures in Ganja are mainly screw-cap and spot-cap lamps; which model suits which control arrangement should be checked in the product information.