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  • Kristján Kristjánsson

Will the new Ēm,u value In The draft of EN 12464-1 “Light and Lighting” be responsible for even more

Updated: Jul 28, 2020

One of the most common complain about artificial light in the workplace is an overabundance use of light. There are many factors why this is a common issue. In my experience one of the factors is that the standards are not properly used. The draft for the prEN 12464-1 Light and Lighting - Lighting for Workplaces, there is an increased risk of over illumination and higher energy consumption.

prEN 12464-1 proposes both the required minimum illuminance values (Ēm,r) which shall be met at all times, but also a recommended higher value for illuminance. It specifies maintained light level over the task or activity areas to fulfil the visual task and is the average minimum illuminance which shall not fall below the chosen value regardless of the age and condition of the installation.


The draft proposes adding an upper level value called Ēm,u, which is up to two steps (at least one step) than the maintained value on the task area (Ēm,r),  to allow for the designed illuminance value (average maintained) to be in this band between the minimum maintained (Ēm,r) and an upper value (Ēm,u).

The above range of illuminance value is specified to cater for differences in visual conditions and user satisfaction. For example, the requirement for writing, typing, reading, data processing was 500 Ēm lx and still is 500 Ēm lx average minimum required light level. However the Ēm,u value is at 1.000lx (two steps than the min maintained). Ēm,u value in this case can be considered as the maximum recommend light level. So if the task area was designed for 1.000 lx, the immediate surrounding areas would then be raised to 500 Ēm lx. Even if the designed average was 750 lx, the immediate surrounding area would still be 500 Ēm lx. It would always make more sense using the current maintained illuminance Ēm. The Designer should be aware of the visual conditions per project needs and should allow for any future changes or needs. At times, higher light levels are needed, and sometimes lower light levels are preferred by the user. Having individual control of light levels is always the best option. The immediate surrounding illuminance values shall always be a function of the task illuminance, for example – task illuminance = 500 lx, then the surround would be around 300lux. There is also the issue in a situation where task locations are not known, specifically an open plan office without defined furniture layout. In this situation, the whole area is to be treated as the task area. This entails that the required illuminance values for an entire office space (task area) would be 500lx Ēm,r lx. to 1.000lx Ēm,u. That would mean recommendations for both surrounding areas and background areas would be the same as the office space or task area in this case. 


In this second revision of EN12464-1, with revised recommendation on lighting solution with emphasis on the user needs is a great step forward. In the past, there have been design decisions made based on the values specified in the standard, disregarding user needs and without a thorough understanding of the standards. Where minimum surface illuminances for walls Ēm,wall and ceiling Ēm, ceiling etc. have been neglected. Having these values in the forefront, contained within the lighting requirement table for better awareness is a positive thing.


Even though the new standard has additional levels of recommendation which is further refinement in the design guideline, this new standard needs to provide better clarification and rational for choosing higher illuminance value ( Ēm,u). Since crucial information have been neglected in the past. Is then possible that the designed Ēm,u value would be used such that Ēm,r = Ēm,u? Ending up with an overabundance of light and greater waste of energy than before. It is not only the task area, but immediate surround and the background area that would also be affected with higher illumination levels.

Now-a-days, most offices have VDT screens. A guide on lighting method is called for, instead of raising already established light levels on work plane. So why is there a need to include an added higher level for the illumination value Ēm,u?

In this day and age where energy consumption is of the highest concern, the Ēm,u value seems to be step backwards.

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