One major cause of discussion about the new LG7 was the issues of illuminance on the walls and ceiling. LG7 included the recommendation that designers consider the amount of light falling on the ceilings and walls to ensure that the room appeared light and gave the occupiers a good visual environment to work in. These recommendation were not new, having appeared in the Code for Interior Lighting since the seventies. Perhaps designers had forgotten about them or had let their attention drift to much towards just providing the recommended illumination levels on the working plane.
The diagram below has appeared in the last four Codes in one form or another. It shows recommendations for room surface reflectance and illuminance levels. The 2001 amendment to LG3 specifically reminded designers that to avoid the room appearing dark they needed to achieve around 30% of the average working plane illuminance on the ceiling and 50% on the walls. In other words if the average working plane illuminance was intended to be 400 Lux the average wall illuminance should be 200 Lux and the average ceiling illuminance should be 120 Lux.
Following the issuing of the 2001 amendment the Society had a lot of feedback from designers and manufacturers about practical problems in achieving the ceiling illuminance levels in spaces with low ceiling heights. The Society reviewed these comments and has modified its recommendations for the new LG7 to include a variations for ceilings below 2.4m.
Where the ceiling height is below 2.4m and the client/developer cannot be persuaded to increase the height, then the designer can provide less that the preferred 30% on the ceiling. The level should not however fall below 20% or the ceiling will look dark by comparison with the rest of the office space which may make it appear oppressive to the occupants.
The Society of Light & Lighting’s Technical Committee agreed the following wording on this issue for inclusion in the new guide - File link