LEDs bring flexibility to emergency lighting design
Fast panic-free evacuation from burning buildings is crucial, which is why UK legislation demands reliable, good quality emergency lighting. Bernard Pratley explains how the latest generation of white-light LEDs provide highly effective escape-route lighting.
Emergency lighting and escape-route illumination must make it easy for people evacuating a building in an emergency, especially where fire is concerned, to see sufficiently clearly to quickly and safely make their way out to a place of safety.
Most people unfamiliar with a building tend to leave it the same way that they entered, often ignoring poorly marked but shorter escape routes. However, compliance with the emergency lighting luminaires standard BS EN 60598-2-22 and the emergency escape lighting application standards BS 5266 series (incorporates EN 1838 and EN 50172) ensures that there is sufficient illumination for people to see and be directed towards emergency exits, with exit or directional signs being in view at all points along the escape route.
Today, nearly all emergency-lighting applications are fulfilled using luminaires fitted with either traditional fluorescent lamps or the latest high-quality white LEDs. The highly successful and economic fluorescents will be around for many years yet, but LED lamps are increasingly providing significant advantages for certain applications.
LEDs have their own very significant advantages for both general and emergency lighting and have been used in exit signs for some years. However, the pace of development has been such that the latest versions are now being used in many emergency-lighting luminaires.
Because individual LEDs are virtually point light sources, control of where the light is aimed is simpler to achieve. Well designed LED emergency-lighting luminaires, with their dedicated optics, can use virtually all the emitted light. The resulting high optical efficiency provides the design illumination with less light than would be needed from a conventional light source. This is one reason for the low energy usage of LED lighting — typically up to 30% better energy efficiency than good fluorescents. Correctly spaced LED emergency luminaires should meet the requirements of BS 5266 with minimum power consumption.
High-quality LED lamps bring many other benefits. For example, they can provide a very long life of around 50 000 h at 70% lumen depreciation. LEDs are highly reliable and virtually unbreakable, so this mix of energy efficiency, reduced lamp replacement and maintenance costs brings a lower total cost of ownership over the life of the installation.
Moreover, LEDs are unaffected by extremely low temperatures, so they can be used in refrigerated areas. Because LEDs are small, groups of them can be made into modules of many shapes and sizes, so they can be designed into buildings, structures and materials in ways that are impossible with conventional lighting. This brings great flexibility for designers and customers alike, avoiding the need for unattractive plastic bulkheads.
Unobtrusive and attractive LED emergency lighting is available in many forms, including flush-mounted recessed luminaires, exit signs and escape-route lighting, including lines of LEDs on strips partially buried in the ground. LED emergency-lighting modules can also be retrofitted into suspended lighting systems and spotlights in applications ranging from retail outlets, hotels, pubs and nightclubs to reception areas.
Good-quality LED emergency lighting products today meet the current emergency requirements in EN 60598.2.22, and are typically based upon two 1 W white LEDs, plus control gear and a 3 h non-maintained battery. Maintained versions are also available. Such fully integrated LED emergency lighting is quick and easy to install, with battery and control gear often housed in a remote pod using plug-in connectors.
A green LED indicating that the charger is working still requires manual checking by maintenance staff. However, automatic test systems, which should comply with BS EN 62034, can be incorporated to measure all basic operation circuitry automatically, and this can be indicated on the luminaire or on a test panel for easy observation and record keeping.
Where LEDs are being offered as user replacement items in maintained luminaires using T8 fluorescent lamps, they must be checked to ensure they operate in the emergency condition and that their light output is adequate for the emergency duty.
Before installing emergency lighting and mains lighting luminaires modified for emergency lighting use, it is essential to leave batteries disconnected until the unswitched supply is no longer subject to frequent disconnection and/or switching, as often happens in new buildings. This will ensure that all emergency lighting luminaires do not need to be re-lamped or have their batteries replaced before commissioning. Advice should be sought from emergency-lighting manufacturers about the suitability of lamps — including LEDs — to operate with their equipment to ensure full compatibility.
Bernard Pratley is with ICEL, the Industry Committee for Emergency Lighting.