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LG3 & Office Lighting

Paul Ruffles Chaired the Task Group that wrote the Lighting Guide ‘The visual environment for display screen use’. Usually referred to in the industry as LG3. Reproduced below is one of the articles that Paul wrote to introduce the 1996 version of the Guide to the profession.

A pdf file version of the LG3:2001 amendment is available on the Society of Light & Lighting website. Click here to go there.

Greater freedom with the new LG3

At the end of March 1996 CIBSE will be launching a new edition of its Lighting Guide LG3. Why has it needed to be revised after such a relatively short time and what are the main implications for the designers and manufacturers that use it? Here Paul Ruffles discusses some of the reasons for its revision and looks at some of the design issues addressed by the new Guide.

The original version of LG3 was issued in 1989 to meet the needs for designers and manufacturers in coping with the increasing use of desktop computers within the working environment. Although the Guide was generally welcome there have turned out to be some problems with its usage.

The most worrying was the emphasis amongst some designers on selecting luminaires purely on their ability to reduce screen reflections, without paying due attention to potential problems that this may cause to the general visual environment of the workplace. To counter this the new edition incorporates more design guidance on the overall visual environment.

The introduction of the Display Screen Equipment Regulations in January 1993 resulted in the Health and Safety Executive issuing guidance to the regulations which referred to LG3 for ‘specific and detailed guidance’ on lighting for these areas. This has lead to the two documents being confused in the minds of some designers and users. Certain lighting manufacturers do seem to have deliberately played on this confusion to sell lights to worried building owners. Because of this, we have spelt out in great detail the interrelationship of the two documents and the legal linkage, or lack of it, between them.

To help the users and designers in their interpretation of the guidance and the Regulations we thought it wise to alter the style and terminology of LG3 to be more consistent with the Regulations and the HSE’s guidance document. Information has been included on the regulations themselves and a section has been added to cover the assessment of lighting in areas where users work with display screens.

The new guide acknowledges that the more widespread use of higher quality screens, and the use of software that uses a light screen background, is reducing the problems encountered with screen reflections. This has been taken into account in the new guide by allowing designers working with known occupiers and screen types more freedom to tailor the lighting to the screens being used and their locations within the working areas.

It has been found that bright skylight from windows and the effect of sunlight on blinds is a major source of visual and screen reflection problem. For this reason the advice and guidance on windows and daylighting has been increased from a single subsection in the old guide to an entire chapter in this guide. The need for lighting designers to work closely with the architects and interior designers has again been emphasised.

Design process

At the heart of the new Guide is a chapter that takes the designer through the stages necessary in the design process to achieve a satisfactory lighting solution. Much of that chapter may seem obvious to some designers but judging by the results of much recent office lighting design it is not obvious to many. Essential is early and continuing liaison with the architect or interior designers over aspects such as room finishes, window design and partition layout. Also essential is liaison with the client or letting agent over the potential screen and other task usage in the space, workstation layouts and operational requirements. The lighting problems will vary widely from control centres, where control consoles with many fixed position screens are installed, to open plan offices with randomly orientated screens of varying types.

Perhaps one of the most tricky areas of design is speculative space for an unknown user. Here it is important to establish with the building owners, and possibly the letting agent, the types of user that the space will be marketed to. This helps to establish the likely types and quantity of display screens that will be used in the space. The space planning flexibility also needs to be established. This will help determine the likely effect of partitioning options on both the illuminance levels and cut-off given by the partitions to long views of luminaires across the space.

Once the usage of screens and the adaptability of the space is known then the physical restraints of the space, such as floor to ceiling height and other building services, need to be thought about before the most appropriate lighting options are chosen. This can be direct lighting onto the working plane from ceiling mounted or suspended fittings; indirect lighting from free standing, wall mounted or suspended uplights or a combination of both direct and indirect lighting. All these systems can light display screen areas well but can also create unacceptable visual conditions if not engineered correctly. Simply specifying ‘LG3’ luminaires is not enough, the effect of the lighting on the appearance of the space and its affect on the users of that space must be considered.

The technical and design requirements for direct lighting, indirect lighting, combined direct and indirect and task/ambient lighting design are each covered by a separate chapter in the new guide. The design requirements have been slightly expanded upon for each of these types of lighting and greater information has been given on the likely pitfalls of poor design for each technique. For indirect lighting the luminance limits remain the same but new criteria for wall mounted uplights have been included. For direct lighting the old three categories have been retained for use in spaces where the designers know nothing about the screens or users that are going to occupy the space – speculative space in general. For areas where the designer is able to determine the types of screen and workplace set up in advance, there are new higher luminance limits available to them with the freedom to determine the most appropriate luminance limit angle for the installation. This last point will allow both designers and manufacturers more freedom to create visually interesting products and spaces that will contribute to better quality lit spaces.


One area of display screen area lighting that is not well understood is that of avoiding screen reflections. The Display Screen Regulations acknowledges that reflections are always present on glass fronted screens and merely requires the avoidance of distracting or disabling reflections. This is to be done by the co-ordination of the workplace and display screens positions with the lighting and window locations in the area. In other words distracting screen reflections can be avoided by careful positioning of the workstations or by advising the screen users on appropriate maximum screen tilts. Only where there is no possibility of control over the screen positions need drastic action be taken on the lighting side.

Also see an article submitted to Design Week magazine which appeared
in May 1997 entitled ‘Glaring mistakes’ here.

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