Riegens Lighting
Lighting Guide 7 - LG7
When designing to achieve these illuminance levels,
care should be taken with the following:
-
The room, where practicable should be
uniformly lit, avoiding high luminance peaks or troughs, against
the average
-
Shadowing, and sharp cut-offs of light on
surfaces, should be avoided where possible
The recommendations for indirect lighting, was
broadly left un-affected within LG7 Office Lighting, but the section has
been re-referenced for ease of use.
When the Cat1 / Cat2 / Cat3 classification system was
withdrawn, a simple system was introduced to classify computer display
screens.
The classification is based on the anti-reflectivity
properties of the individual screen, ranging from I, (good), through to
III, (poor).
One area that is often misunderstood is the
applicable lighting standards and recommendations for office interiors.
Combining the right luminaires, in the right
application, with the correct amount of light, is a skill. Our
experienced designers work with these challenges everyday and are well
placed to offer advice and guidance.
In 1989 the Chartered Institute of Building Services
Engineers, (CIBSE), introduced a code of practice for lighting interior
office environments. The guide, LG3, concentrated on areas where
computer terminals were in operation. The lighting section soon became
wrongly administered and broken down into its basic component parts.
It became normal for areas within projects to be
specified as a maximum luminance, or brightness. LG3 contained
parameters that limited luminance above certain viewing angles and the
terms Cat 1, Cat 2 and Cat 3 came into everyday lighting language.
Unfortunately, when these rules were applied, office
interiors often ended up as dark and gloomy workspaces, especially the
upper areas of the walls, above the cut off angle and the ceiling.
In 2001, an addendum was drafted, the guide
re-vitalised and re-issued.
This removed the categorisation system for luminaires
and reminded designers of the necessity to consider the lighting levels
of the walls and ceiling in relation to the working plane.
In 2005 a new and completely rewritten edition of
Lighting Guide 7 was released. The new LG7 covers all aspects of
lighting for offices, from board rooms through general offices to the
post room. This new publication effectively replaces LG3 as the relevant
guidance for office buildings. However, there are many other buildings
where display screen equipment is used. Lighting Guide 3 (now out of
print) still provides useful guidance for such applications.
The guide takes in to consideration the release of
the 2002 European Regulations, regarding lighting in the workspace. BS
EN 12464-1 2002, is considered by many to be on a par with the LG7 :
Office Lighting.
The LG7 guide emphasises the need for a greater
understanding and thought on all aspects of office interiors. Lighting
design, and the output and control of light from luminaires, must be
viewed in partnership with daylight and the computer screen position and
geometry. Although the guide is extensive, key parts will play a
fundamental role when approaching an interior office lighting design.
With specific emphasis put on reflectance properties
of the area, task illuminance limitations, daylight, and types and
methods of lighting the area, the guide aims to encompass all aspects.
If the type of screen class, software style and
position is not known, then a set value of a maximum of 200cd/m2 when
using direct lighting, or 500cd/m2 if using indirect lighting at a 65º
angle of elevation or 55º in special circumstances. If other parameters
are used, it is important to state any assumptions that apply, this will
allow the user to take informed responsibility.
To follow the guidelines and correct practice of LG7,
both the specifier and the installer are required to complete
certificates of conformity, stating that the code has been met.
The certificates collate all the relevant information
with regard to the area being lit into one document and covers surface
reflectance used for the design, surface treatment of the display
screens including the type of software being used (positive or
negative). Details of the luminaires, direct, indirect or a combination.
There is also an opportunity to include a statement
as to why the scheme does not comply with the guide. This could be that
the installation positions of the luminaires are determined by the
structure of the building, or that the windows are continuous above the
sill, and therefore it is not possible to mount uplighters around the
exterior walls.
At Riegens our experienced and dedicated design team
are conversant with all aspects of interior lighting design, and we
pride ourselves on our ability to help and steer are customers through
all aspects of LG7.
For more information, or for help and advice, simply
contact your local Riegens sales office or visit www.riegens.com
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