Have we reached the point where specifiers, installers and users of emergency lighting will accept LED unquestionably as the light source of choice?
An increasing number of people would say yes, such has been the growth of LEDs in the market, and the almost universal acclaim for their benefits.
LED products tick the box for practically every photometric parameter. Lamp life is clearly an overwhelming advantage, with the additional benefit of energy savings. LEDs have also enabled the development of a new generation of sleeker, more compact emergency luminaires, while retaining or improving the quality and distribution of light – a big plus for architects and designers.
But incandescent and fluorescent aren’t dead yet. T5 solutions could still be regarded as feasible if not desirable for some installations. And there are still question marks – although these are becoming rarer and rarer – about LED lamp quality.
So it’s an appropriate time to assess the pros and cons of LEDs in emergency lighting.
LED emergency lighting products may appear not to stack up when you compare the cost of the luminaires themselves to the alternatives. But when you consider whole-life cost, then LED luminaires will mostly win. For example comparing a typical 8W maintained self-contained bulkhead with a LED equivalent, then the cost comparison ratio will probably be of the order of 1:2 to 1:4 respectively.
But let’s look at the cost of lamp and battery replacement over an eight-year period. They’ll both need one battery replacement in that period, but the big difference is that the 8W bulkhead will require at least eight lamp changes over the same period, with each change probably costing at least the initial cost of the 8W luminaire. If energy consumption is also taken into account (see below) then the case for LEDs is even stronger.
Comparisons of energy consumption between fluorescent and LED emergency luminaires generally have LED luminaires coming out on top. Normally LED luminaires will use less than half the energy and fewer luminaires will be required, as controlling where the light goes is easier. A comparison of an emergency lighting scheme using 200 x 8W fluorescent self-contained luminaires showed that only 130 LED self-contained luminaires – using less than a third of the energy of the old scheme.
The perceived glare from LED emergency luminaires has been reported by some as being an issue, but the glare should be within the limits prescribed in EN1838 and as such will be acceptable in an emergency lighting scheme (ICEL, the UK’s Industry Committee for Emergency Lighting, has noted this issue and will be doing some further research to see if glare limits need to be changed).
As mentioned above, the cost of replacing the lamp in a typical 8W fluorescent emergency luminaire could often be more than the cost of the luminaire when labour is taken into account. Meanwhile a well-designed LED luminaire may not require the light source to be changed at all throughout its service life.
Additionally as 8W fluorescent lamps degrade prior to failure, the ends blacken, and they produce far less than their rated output, even though they’re still operating. In these circumstances it is possible that the rated output and design illuminance are not achieved. LED degradation for good quality LEDs in well-designed emergency lighting luminaires is much slower and the rated light output of LED luminaires achieved for the service life of the products.
Controlled light distribution to illuminate high-risk task areas
As previously mentioned the LED is effectively a ‘point source’ light, so it’s easier to control the light distribution to make sure the light only goes where it’s required. In addition to the ability to illuminate the escape routes and open areas particularly effectively, this makes using LED luminaires a good choice for highlighting specific tasks and hazards in a mains failure situation.
As LED efficacies improve, the amount of light required versus the power required by the LED light sources to illuminate escape routes and open areas means that the heat produced from operating LEDs is becoming less of an issue. Furthermore the move from luminaires using a few high-power LEDs to using a greater number of medium-power LEDs further reduces the heat generated. This is particularly pertinent for self-contained luminaires where the battery (a key temperature sensitive component) is contained within the luminaire. Keeping the battery cooler in service normally assures a longer service life.
The requirement for emergency lighting is to use light sources with a colour rendering index (CRI) greater than Ra 40. That’s pretty low, so it means the quality of light for an emergency luminaire needn’t be that good. But as the requirement for mains lighting drives improvements in the quality of light, emergency LED luminaires with CRIs as high as Ra 80 are not hard to find.
The quality of the lamp source
Similarly, mains lighting requirements and the development of standards for testing LEDs, LED driver modules and luminaires means that the performance of LEDs is much better understood, this means that with careful design, emergency LED luminaires with a life expectancy of up to 50,000 hours are possible. Note that if the emergency LED luminaire is non-maintained, only operating when the normal lighting supply fails, then LEDs will last the lifetime of the product with minimal reduction in light output, as the LEDs only operate in emergency.
Re-engineering existing luminaires to sustained emergency operation using LEDs
Existing mains luminaires, such as T5 fittings are now being re-engineered into emergency luminaires by the addition of an emergency LED source rather than using the existing T5 lamps as the emergency lighting source. As long as the re-engineering process is handled correctly by following the ICEL 1004 guide, then this is a perfectly acceptable way of achieving the desired emergency luminaire.
The examples of really excellent emergency lighting schemes using LEDs shows beyond all reasonable doubt that LED can now rightly be classified as the light source of today.
We must however also point out that it is not the single panacea. ICEL members are committed to quality and reliability as well as value for money, and will take all these factors into consideration when putting a scheme forward. While we have no particular axe to grind, the fact that our catalogues and websites are increasingly filled with LED products will help you to draw the obvious conclusion.
Alan Daniels and Martin Afford are both members of the technical committee of ICEL, the UK's Industry Committee for Emergency Lighting. Daniels is technical director of P4, and Afford is technical manager of Emergency Lighting Products (ELP). Head to www.icel.co.uk for more information, or contact email@example.com