Forget emergency lighting – the future's ‘stay-put’ lights

Conventional wisdom says that, in the event of an electrical failure in a commercial building, one of two things should happen; either people evacuate the building with the aid of an escape lighting installation or work goes on as normal because there is a stand-by electrical supply enabling everyone to continue about their business. But is this good enough?

After all, unless there are alarms sounding off everywhere, there is no emergency to speak of. It’s just gone dark. It’s just a loss of power, so why should business grind to a halt?

Levels of illumination for escape lighting are very low, the principle being that escape lighting guides people from illuminated sign to illuminated sign along dedicated routes until they reach the final exit from the building. The lighting levels that are generated by the escape lighting offer nothing more than providing the mesopically-adapted eye (the mode we use for viewing in low-light levels such as moonlight) with the means to avoid hazards along the route, nothing more.

On the other hand, a standby electrical supply, provided either by a generator or a bank of  batteries is intended to restore the usual illuminance levels. This makes it very expensive and most businesses cannot cope either physically or financially with such a facility, so perhaps we need find a third way that is manageable for business without putting anyone in danger. This third way is being discussed and it’s called ‘stay put lighting’.

According to the Health & Safety Executive (HSE), which is the body responsible for workplace welfare in the UK, the minimum illuminance level needed for general movement of people in a building is 20 lx, with a minimum measured illuminance of 5 lx. If we compare this with the typical 0.5 – 1 lx required for escape lighting it’s quite a performance gap, but its looking more likely that new technologies can help to bridge it.

Developments in two areas of electronic research suggest that stay put lighting may not be as far away as we imagine. Improvements in the luminous efficacy of the LED is well documented, and LED manufacturers report almost daily that there are even more efficient sources in the pipeline. If we can radically increase the lumens/W performance ratio, that suggests that it may soon be possible to imagine an overall 20 lx average illumination becoming available for workplaces and retail spaces.

The other area of development is well known to everyone, but is rarely seen. More light only works if the power supply is small enough and powerful enough to last the course. And it only makes sense to stay at one’s desk or to continue with a shopping trip if work can still be done. That means we will be depending on battery-powered devices, from computers, through mobile phones to shopping tills, all of which are powered by slim lithium-ion (Li-Ion) batteries, rather than a bulky NiCd battery. It’s this technology that’s being developed for use in electric vehicles.

There is no reason why the emergency lighting sector could not benefit from these leaps in technology and provide an affordable ‘stay put’ lighting strategy for the modern business environment. And we could also stop worrying about all those old stashes of cadmium ending up in landfill.


  • Stay-put lighting is the subjest of a special Lux Webcast taking place on Wednesday 11 October at 1pm BST. The expert is Alan Daniels of P4 Fastel. To register for the free webast and see more information, click HERE



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