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Topic Title: Office Lighting levels
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Created On: 28 January 2013 07:09 PM
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 28 January 2013 07:09 PM
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SKElectrical

Posts: 911
Joined: 01 February 2009

Can anyone tell me minimum lighting levels at desk height for an average office.
Thanks.
 28 January 2013 07:50 PM
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GB

Posts: 368
Joined: 04 September 2002

between 400 and 500Lux average across ta general office area, you will find that any reading taken directly below a fitting will tend to be quite high so its the average across the room area (excluding 500mm perimeter)
 28 January 2013 08:00 PM
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SKElectrical

Posts: 911
Joined: 01 February 2009

thanks, its probably in CIBSE table somewhere but I couldn't find it.
 28 January 2013 08:33 PM
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GB

Posts: 368
Joined: 04 September 2002

That is for a general office area, you may need higher lighting levels for a drawing office or for specific task lighting.
 29 January 2013 09:20 AM
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OMS

Posts: 19900
Joined: 23 March 2004

CIBSE Lighting guide 7 would be a good starting point.

As for a minimum, first decide what your average should be (say 300 - 500 with a design intent to the lower bound) - from there you neeed to determine your uniformity ratio and from that what your minimum can be

ie Uniformity = Eaverage/Eminimum - where E is illuminance in Lux.

Using sensible wall to task or ceiling to task illuminance ratios indicates to me that your low points in an average office (say 400lux avearge) should be around 200(ish) lux (exluding the room border or circulation ways) - your upper bound would be above 600 point illuminance and probably over 700 on day 1 ie an increase of 1/maintenance factor.

If you are trying to determine if an installed solution is aceptable take a look here - navigate to Fact File No 3.

That should give you a starting point.

Or did you actually want the lower end of the average maintained illuminance target ? - 300 - 400lux would be sensible, for avoidance of your design risk aim for about 450 upwards with 0.7, 0.5 and 0.3 room reflectances and specify regulating ballasts (and then of course the relevant controll photocells,absence detection etc) - that way you can modulate the output to account for daylight or if a client prefers (within reason) a higher or lower value from your 400 lux midpoint criteria.

Regards

OMS

-------------------------
Failure is always an option
 29 January 2013 12:48 PM
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broadgage

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My personal view, not supported by any regulations, is that the accepted figures of about 300 to 500 lux are far too high.

A large part of my work is the day to day maintenance of offices. A very frequent request is to remove lamps or luminaires because the user finds it too bright.
A recently refurbished office had an average light level at desk height of 450 lux with brand new lamps and fittings.
Well over half the lamps have been removed because "it was too bright"
I measured only 150 lux in one area, which was still considered too bright.

The practice of removing lamps or unplugging luminaires is very common, and usually harmless, but a matter of some concern if someone removes the lamp from an emergency fitting.

In my view, dimming fittings should be seriously considered for new office fit outs.

For my own use I favour at least 500 lux from daylight flourescent tubes, but I am in a minority re this.
 29 January 2013 01:56 PM
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amandalewin

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Originally posted by: broadgage

My personal view, not supported by any regulations, is that the accepted figures of about 300 to 500 lux are far too high.



A large part of my work is the day to day maintenance of offices. A very frequent request is to remove lamps or luminaires because the user finds it too bright.

A recently refurbished office had an average light level at desk height of 450 lux with brand new lamps and fittings.

Well over half the lamps have been removed because "it was too bright"

I measured only 150 lux in one area, which was still considered too bright.



The practice of removing lamps or unplugging luminaires is very common, and usually harmless, but a matter of some concern if someone removes the lamp from an emergency fitting.



In my view, dimming fittings should be seriously considered for new office fit outs.



For my own use I favour at least 500 lux from daylight flourescent tubes, but I am in a minority re this.


I get into the office at around 9 and am always the first person to turn the lights on! My colleagues seem to like sitting around in the dark in front of their computer screens but if I sit in the dark I just want to go to sleep

I think the lower end of the 300-500lux bracket is ok for people just using computers but if you are doing any kind of paper based work it's better to aim for 400-500lux.

-------------------------
Amanda

'At some point we all must chose between what is right and what is awesome'
 29 January 2013 02:11 PM
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OMS

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I get into the office at around 9 and am always the first person to turn the lights on! My colleagues seem to like sitting around in the dark in front of their computer screens but if I sit in the dark I just want to go to sleep


Switch your PC on and look at it for a few minutes - the blue part of the spectrum will influence the pineal gland and change the melatonin levels - you can't really be tired if your in consultancy and don't get in till 09.00 -

seriously, I was involved ins some research a while back and one of the off shoots of what we were looking at was shocking the body systems with some quite bright light during the day - so don't underdesign offices lighting - some like it bright. Better to have a system capable of meeting relatively high values but then arranged so you have daylight linking and even dimming control by the user in small areas (or even per luminaire).

Just don't make the mistake i did on a job where we had the desk phones capable of "calling" the luminaire and then using the key pad to adjust that luminaire up and down - we never figured that people in distant parts of the office would note down luminaire addresses and then amuse themselves by dialing someones luminaire at random and fiddling with it - such fun -

regards

OMS

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 29 January 2013 06:47 PM
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SKElectrical

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been asked to assess light levels as office staff feel it isn't bright enough. Why oh why they need a machine to confirm what they already know is a little bizarre (took 9 attempts to spell that correctly).
I would have thought they would just ask to swap lamps for brighter colour - say 890s (my favourite for utility rooms, im sad aren't I?)
 29 January 2013 07:14 PM
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OMS

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Changing the lamp colour temperature isn't really going to achieve appreciably more lumens and the effect is pretty well subjective anyway in my experience.

The only way to determine if the illuminance is low is to measure it - fact file 3 will give you the procedure.

If it's obviously low, then a redesign and upgraded installation may be easier to do than measuring and reporting in the first instance.

Just a word of warning - staff making claims about low light levels often masks other problem areas of thier employment - just be minded someone isn't talking to HSE or an employment law specialist.

regards

OMS

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Failure is always an option
 30 January 2013 12:29 PM
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amandalewin

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Originally posted by: OMS



Just a word of warning - staff making claims about low light levels often masks other problem areas of thier employment - just be minded someone isn't talking to HSE or an employment law specialist.



What do you mean by this? Just interested as I once did a survey of the lighting levels at a well known bank that was making a lot of job cuts and was surprised by how many complaints there were about the lighting levels.

-------------------------
Amanda

'At some point we all must chose between what is right and what is awesome'
 30 January 2013 12:49 PM
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OMS

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Sounds about right Amanda - lighting, temperature and humidity become a significant cause of complaint in a disgruntled workforce - they can't easily fight the bullying, working hours, demands, attitude etc etc - so they pick on the subjective aspects they can complain about.

It was just a word of caution that if you get dragged in to measure and report on these sort of issues, they are rarely the real issues - but they will be scrutinised in some detail (more than is reasonable or usual) - trade union reps, worklace reps and a few quasi legal people just love to point out that the consultants report/assesment is flawed, inaccurate etc. It gets worse if there are issues of landlord consent or if the space is leased with Cat B fit out etc

It's a great game we play - don't you just love consultancy

regards

OMS

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Failure is always an option
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