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517

LIGHTING SOLUTIONS

CA452001EN - March 2015

Technical

Interior Lighting Design

There is a wide range of lighting application standards and guides

available to aid the designer in creating a comfortable and efficient

working space.

The recent updated edition of BS EN 12464-1:2011, which not only

sets a standard for illumination levels for specific tasks but, also

provides advice on how to achieve a lighting solution to meet the

human need. Also the SLL Lighting Design Guides provides a very

good source of guidance for the design of working spaces, and can

be considered as best practice. Lighting Guide (LG) 7 is possibly

the one most commonly referred to, but it is often misunderstood

being used to specify luminaires rather than the total environment

of the space.

LG7 was written to supersede the original LG3 which had very

restrictive cut off criteria for the luminance of luminaires. With the

development of improved and flatter VDT screens this could be

relaxed, allowing for higher luminance values from the luminaire.

The increase being 3000 cd/m

2

or 200 cd/m

2

if the screen type

is unknown. This can be increased up to 1500 cd/m

2

and 500 cd/

m

2

respectively if positive polarity software only is used. LG7 also

recommends values for the wall and ceiling illuminance, which are

based on a direct percentage of the working plane level.

The intention being to alleviate the “cave like” appearance that the

single use of the original Category 2 cut off luminaires produced.

The LG7 lighting guide for office lighting was amended in 2012

to align with EN12464-1. This changed the recommendation for

the wall and ceiling illuminances to be a percentage of that of

the working plane to specific levels of illumination (lux) with a

minimum uniformity.

In addition the recommended range for the Cd/m

2

for luminaires

at the relevant cut off angle was changed and now has a range of

1000-1500 Cd/m

2

for screens having luminances (brightness) of

less than 2000 Cd/m

2

which increases to 3000 Cd/m

2

for screens

with higher luminances.

It must be stated that LG7 is often referred to as being guidance

for luminaires but it was written as a complete guide for lighting of

the office environment, taking into account the total need of the

occupants to create pleasant working space.

Recommendation for Wall and Ceiling Illuminance

The guide provides recommendations to address the dark and

gloomy effect that can be created by ‘categorised’ louvres,

including the sharp wall cut off and bright scalloping. To avoid

this, walls and the ceiling should be lit as follows:

- The average wall illuminance above the working plane

should be at least 75 lux with a uniformity of >0.1

- The ceiling average illuminance should be at least 50 lux

with a uniformity of >0.1

The other misconception is that office lighting is all about creating

a uniform lighting level across the whole space. What is needed is

uniform lighting across each task area, which normally consists of

relatively small areas on each desk. The lighting in the wider office

space can, and indeed should, vary somewhat to create visual

interest. Even the most dedicated office worker looks up from his

or her work from time to time, and when they do they need to see

an interestingly lit office space and, ideally, a more distant view out

of a window.

If the building and the visual requirements of the users of an

office space are understood and all possible lighting options are

considered, a lit environment can be created for each office space

that not only provides the required levels of lighting for each task

but also provides an interesting and stimulating lit environment for

people to work in.

This is a direct quote from the introduction of LG7 which goes

on to discuss the whole design process. The overall intention of

the guide has not been fully utilised by the majority of users and

the reliance on a “single luminaire solution” has still been widely

requested. The single luminaire approach when used in regular

arrays to produce a high level of uniformity across the whole

working space can be in contradiction to the original intent.

If designing to LG7 the certificate of conformity should be used to

show the criteria of the design.

Certificate of Conformity

The guide requires that the designer and installer of the

installation complete and sign a Certificate of Conformity to

demonstrate that all known visual and ergonomic criteria were

fully considered during the design process and installed as

specified.

Due to the regular development of these guides, Eaton

recommends you visit CIBSE on

www.cibse.org

to ensure the

latest guides are being referred to.

EN12464-1:2011

The lighting design standards detailed in EN12464-1:2011

break the design process into a number of key elements to aid

the design process. It however is not intended to provide

specific solutions, nor restrict the designer from exploring new

techniques or restrict the use of innovative equipment. Daylight,

as well as artificial light, should also be fully utilised for both

quality and to reduce energy.

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