Emergency Lighting and Dimmable Drivers

Emergency lighting is the system that operates when the mains fails. Its purpose is not comfort but safety: to illuminate escape routes, identify hazards, and support orderly evacuation when every other light in the building is off. Because it is a life-safety function, it is governed by standards and building codes that prescribe where luminaires must be installed, how long they must operate, and how they must be tested. Drivers that serve emergency luminaires carry obligations that ordinary dimming drivers do not.

The product standards are specific. IEC 60598-2-22:2021 sets the particular requirements for emergency lighting luminaires, covering construction, performance, and testing for luminaires operating from emergency power supplies not exceeding 1000V. At the system level, BS EN 50172:2024 specifies the installation, verification, operation, and maintenance requirements for emergency escape lighting systems in non-residential buildings, including the periodic testing that keeps systems functional. These two documents define what emergency luminaires are and how the systems around them must behave.

The central design decision is the mode of operation. A maintained luminaire contains a lamp that runs continuously during normal operation and continues to run from the battery when mains fails; its driver is active all the time. A non-maintained luminaire is normally off and lights only when the mains fails, drawing power exclusively from the emergency source. Both modes affect driver selection. A dimmable driver in a maintained luminaire must not leave the lamp at minimum during normal hours in a way that defeats the emergency requirement, and in a non-maintained luminaire the emergency converter, not the normal driver, controls the lamp.

Constant-voltage drivers appear in emergency systems in two ways. The first is as part of a self-contained emergency luminaire, where a battery-backed converter module takes over the LED load when mains fails. The second is in central battery or central inverter systems, where many luminaires are fed from a shared emergency power source. In both cases, the 24V bus and the LED modules must be compatible with both the normal driver and the emergency source, and the changeover must not produce a gap in light output longer than the code allows. This is why emergency luminaires are usually tested as complete assemblies rather than as driver plus module.

Testing is the part of emergency lighting that is most often neglected. Codes require functional tests at defined intervals: typically a short monthly test to verify that the luminaire switches to battery and operates, and an annual full-duration test to verify that it can run for the rated period, commonly 90 minutes or 3 hours. Modern self-testing emergency luminaires automate both, reporting failures and battery health through an indicator or a monitoring network. Specifying self-testing units removes the human factor that otherwise lets batteries die silently between inspections.

For the specifier, the practical questions are three. Is the luminaire certified to IEC 60598-2-22 as a complete emergency luminaire? Does the system design and test schedule follow BS EN 50172 or the applicable local code? And does the normal dimming driver leave the emergency function intact, for example by never dimming a maintained luminaire below the emergency requirement? A dimmable driver like the PV100 is appropriate for the general lighting circuits around an emergency system, but the emergency luminaires themselves are a separate, certified product category with their own rules.