Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This first Question of the Day, concerning luminaires and lux levels for general office lighting, is answered by Thorn:
Lighting is not my field, and I can't get anyone to help on this issue. The office is to be leased from a developer who has M+E consultants who don't seem to have the answer I seek. The tender is to be let shortly and I have an opportunity to influence an alternative light fitting.
The specification is for design build, and the specification for the lighting says that maintained luminance shall be 400lux in office areas. The cleaning intervals must be two years for luminaires, plus a four-year lamp replacement cycle, assuming 225 hours use/annum.
The STS manangement team has seen a similar office on site to the same specification and considers the lighting to be dim, and not good enough. I am told that 400lux is normal lighting standard for this type of office and that it must be down to the type of lighting fitting, which seems to be a shaped diffuser type. But, I get the impression that it has been left to the contractor to design this and price may have a bigger persuasion than technical merit.
Can you assist in telling me whether 400lux an acceptable lighting level for this situation? Also, what is the best type of fitting to achieve the optimum light for an open plan office environment? I am told that lighting fittings have changed to diffuse light so that computer screens are more easily seen and this might affect the situation. Is this so? Is it possible measure to ensure that 400lux has been achieved? Finally, how big an effect does ceiling and other colour have on lighting level achieved, assuming the use in this application of light pastel coloured walls and ceilings.
Answer: There are a few things to address here: The first being the lux level, generally speaking 300lux to 500lux is the amount required for general office environment for desk based tasks, however you mention a drawing office which may require more (The Society of Light and Lighting recommendation is 750lux for drawing boards specifically). Bare in mind though that these are simply recommendations and it is important that you evaluate what works for your type of work.
There are a wide range of luminiares specifically designed for office use. These vary in appearance and price. Ensuring that the lighting meets the performance, efficiency and comfort criteria for people allowing them to use computers and complete other tasks without worrying about glare is important. To do so you should specifiy that you lighting design complies to Lighting Guide 7 - lighting recommendations designed to ensure that an office installation doesn't have dark ceilings or dark walls, thus making sure there is a comfortable balance of illumination on the room surfaces. LG7 is available from the SLL website, or you can simply add it to your specification. Avoid luminaires that simply meet the Category 2 standard which became defunct many years ago. Try instead to use luminaires that have an element of upward light back onto the ceiling.
Yes you can check if you have 400lux. Light can be measured with a simple light meter (available from a wholesaler).
Lastly, ceilings, walls, desks, carpets, everything does have an effect on light levels. There are many factors to address when designing a lighting scheme for an office (or any installation) - reflectance, colour, windows, glare etc. But these should be calculated when a lighting designer completes a scheme for you.
You can see our full range of luminaires on our website www.thornlighting.co.uk or ring Thorn Technical directly on 0870 600 8111 0870 600 8111 and I'll be happy to email you some fittings info over. I can also assist with contacting a Sales Engineer in your area who can help you chose the fitting that meets your requirements and also do a lighting design plot for you to ensure you get exactly the correct amount of fittings to meet your required lux levels.
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