It’s an emergency – so why can’t I see where I’m going?

HAVE YOU ever seen 1 lux? It’s pretty much dark. 

The emergency lighting standard BS 5266: 2016 has lots to commend it. I especially like the concept of ‘stay put’ lighting and the requirement for higher levels of illuminance in high risk areas. 

Where I diverge from the expert authors is the 1 lux minimum along the centre of the escape route. 
As an example, I once received a rather worried phone call from a firm of consulting engineers. The story was that there had been a power failure the previous evening and ‘the emergency lights didn’t work’. Luckily, there hadn’t been an emergency; no-one was injured and no harm had been done. Could I come straight away to investigate?
 
The staff were worried and said that the whole open-plan office had been plunged into total darkness. After taking lux readings, the lowest measured values I found were well above 1 lux. After further investigation, the cause of the problem was simply that during normal use, the office was lit to 500 lux. If your eyes are adapted to that level of illumination and the lights suddenly go off, 1 lux is pitch black and you can’t see where you are going until several seconds have passed. 

 If your eyes are adapted 500 lux and the lights suddenly go off, 1 lux is pitch black



This aspect of adaption is picked up in the 2016 issue of the SLL Lighting Guide 6 to the Exterior Environment where it says that outdoor escape routes (from the exit door to the muster point) should be illuminated to a minimum of 5 per cent of the illuminance immediately inside the building. 

In principle, the Fire Risk Assessment for the building would highlight the need for more than 1 lux in escape routes moving from brightly lit offices.  It’s true that BS 5266 says this is the minimum illuminance and it can be higher, but budgets will always drive levels to the lowest basic requirement. As such, I still feel that the standard should recommend a higher baseline value.

Related to this is whether, during routine testing, the illumination level is verified to see whether it conforms. There are many excellent auto-test systems available but measuring the actual illumination requires a competent engineer with an accurate lux meter to walk the escape routes. Maybe a decorator has accidentally painted over one of the lights? 

Unless you know what you are doing, measuring illumination at these low levels can lead to serious inaccuracies. There are two main factors involved. The first is the light output from the luminaire and I strongly recommend that it is supplied with third-party performance verification such as that provided by ICEL. The other factor affecting the illumination level is the spacing between the luminaires. Obviously, if they are too far apart, they won’t achieve the required illuminance. Again, you should use ICEL approved spacing data.

Many professionals who specialise in emergency lighting would argue that using approved certified products with third-party accredited data is a better way of assessing performance. 
Some organisations such as Transport for London take these measurements regularly. I have also heard that some hospitals also verify their emergency lighting levels. However, there is often a deafening silence when I raise this issue amongst building and estates managers.
 

  • Emergency lighting standards and best practice will be the focus of the Escape Zone at LuxLive 2017 exhibition on Wednesday 15 November and Thursday 16 November 2017 at ExCeL London. The Escape Zone arena features a rolling programme of presentations, demonstrations and panel discussions about emergency lighting. See more information and register HERE

Comments 1

Totally agree 1 Lux is riduclously low but LED is driving up LUX readings significantly. The hope now is that building Managers move to energency efficient "Smart LED" along with lithium ion is the emergency lighting solution.

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