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Impact of batteries on emergency lighting evolution

Posted: 06 Jul 2015     Print Version  Bookmark and Share

Keywords:emergency lighting  battery  NiCd  nickel cadmium  luminaire 


Other benefits of NiMH is the absence of any heavy metal such as cadmium, which means they are not subject to recent European legislation which sought to ban the use of cadmium in all re-chargeable batteries. However the EU, recognising that emergency lighting was a special case has given a special dispensation, under the auspices of the Battery Directive, to this particular sector to allow the continued use of NiCd. But there is a caveat; with manufacturers being obliged to instigate a comprehensive recycling programme and declare their success or otherwise at meeting specified recycling targets. So whilst the NiCd batteries may be both cheaper to manufacture and are ideally suited to the emergency lighting application, the additional cost of the recycling programme is also forcing the industry to look for yet another alternative.

The current estimate from Tridonic is that 30%—40% of emergency lighting luminaires are now utilising the smaller NiMH batteries, despite a significant increased cost over NiCd that would provide an equivalent performance.

Where are we now and a sign of the future
There is no doubt that the requirement for smaller LED luminaires will continue as designers continue to demand ever slimmer luminaires for the sleek interiors expected in any 21st century building. One attractive option is the Li-ion battery as it can be produced in a variety of finished forms. Tridonic is now leading the way in the development of such technologies and firmly believes that this could be the way forward. These new batteries are a highly attractive alternative to the NiMH models as they are about 60% of the equivalent size compared to NiMh and each cell provides 3.7V in comparison to the 1.2V of each cell in the NiMH battery. This means that a three cell battery can be replaced by a single cell battery that is actually cheaper, however it is never that simple. The big problem is that due to the volatile nature of Lithium ion, charging is made much more difficult. Managing the charging characteristics is key and each battery requires an electronic protection circuit that will monitor the condition of the battery and shut it down if it becomes unstable.

A further consideration is what happens when a battery needs replacing. All NiCd batteries designed for emergency lighting are interchangeable, making maintenance relatively easy. With Li-ion the replacement cell needs to be an exact replica and the emergency driver unit will conduct a 'handshake' check to confirm it is the right unit prior to charging recommencing. This additional built-in electronic capability obviously adds to the cost, bringing them back in line with NiMH prices. On the upside, once the Li-ion battery has been charged it will then retain its charge for a long period of time, far longer than the NiMH, so overall choosing Li-ion can deliver a significant energy saving when you consider the number of emergency luminaires likely to be found in any one building.

Both observers of the lighting industry and the key players have been surprised by how quickly the switch to LED has taken place, many being caught out by the market's willingness to change. It is not going to be as quick or easy when it comes to emergency lighting power supplies. Tridonic believes that for some applications the Li-ion option will be the way forward in the next couple of years and that will coincide with the proposed 2016 European review of legislation. At this stage it is still unclear if the collection targets of 45% for NiCd will be met and just what the ramifications would accrue. But that is not the end, there are other energy sources that have yet to be fully explored including super capacitors and hydrogen fuel cells, but those are for discussion at a later date.

The old candle solution was actually very clever. Even if you leave it untouched in a drawer for 10 years, providing you have the correct convertor your emergency light source will perform. The challenge in the 21st century for luminaire manufacturers is to develop a battery with an equivalent level of reliability compared with the candle but which meets the safety and style requirements of a modern generation.

About the author
John Kears is Product Manager for Emergency Lighting at Tridonic.

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