Glaring mistakes

Often designers get the focus wrong when lighting an office full of VDTs. Paul Ruffles gives some tips. Paul Ruffles is the chairman of the CIBSE Lighting Division and is Principal of Lighting Design & Technology based in Bath.

Why is there so much concern about the lighting of offices where visual display terminals are used? The screens themselves sit there glowing happily whatever the lighting of the room. Of course, the lighting isn’t there for the benefit of the screens but for the poor mortals who have to operate them. Even if you are quite comfortable with the lighting around your VDT screen and in the room, you are probably aware that there can be problems with reflections on the screen and poor contrast between the screen images and the room background.

These problems are often easily overcome. The first and most common problem, that of screen reflections from windows or lights, is usually solved by moving the screen or re-orienting the workstation. When this is not possible, action must be taken to limit the brightness of the windows or the lights.

Altering the brightness of the windows, or rather the brightness of white clouds seen through them, is not as easy as it seems. The window is an important source of contact with the outside world, and if it is screened off completely then there can be a sense of disconnection, especially for people whose workstations are remote from the windows. It is better to try to screen the high bright areas of the sky by using a simple roller blind or horizontal venetian blind, as this maintains some view out in the lower part of the windows. Curtains or vertical louvre drapes that have to be drawn across the entire window can often cut out the view. Whatever method you choose, simple local control and adjustability of the screening is important. People then feel more in control of the environment and can determine the exact degree of shading or admission of daylight.

You should remember, however, that the window is often also a source of direct sunlight, which can be a cause of considerable discomfort, especially for people sitting near to windows. Where there is direct sunlight coming through a window it is important that any screening is high-density, otherwise it will simply turn into a large, bright object when the sunlight hits it, providing a source of glare, distraction and screen reflections for most of those in the room. Where the windows provide a means of ventilation, the screening system must be selected to allow people safe and easy access to the window catches.

The subject of selecting lighting systems for offices is always controversial. There are many lighting designers or manufacturers who will advocate one magic solution or another – uplighting, highly controlled downlights or perhaps task lighting. All these systems can work well if correctly chosen for the types of screen and environment that they are intended for, but – and this is a big but – they can all be disastrous if misapplied.

Sharply controlled downlight in a room with rather dark carpets and furniture can result in a very gloomy environment. Uplighting in a room with low ceilings can result in hot-spots on the ceilings which appear as bright blobs on the VDT screens. Where there is an adequate ceiling height, a good general solution is some form of suspended fitting offering a combination of direct and indirect lighting. This provides soft background light from the ceiling with some direct light to give good modelling and working light.

In terms of the balance of lighting between the workstation and the wider office, this is an area that is often overlooked by many lighting designers, but can be most important for the users of the room. Poor balance of the lighting can leave the screen operator working in a pool of light while the room around appears gloomy or oppressive. Conversely, bright windows or brightly lit room surfaces along the line of sight beyond the screen can be most distracting. Again, getting the right sort of light in the right place is the most important way of getting a good balance of light in a room. Light too near the walls can cause bright flashes, but lights too far from walls can make them seem dark.

Just remind anyone who talks to you about “lighting for VDTs” that the screens can take care of themselves – it’s the people who use the screens who should be considered when the lighting is being planned.

LIGHTING SYSTEMS

There are four types of lighting systems that can provide acceptable lighting conditions for VDT areas:

General downlighting – recessed into, mounted on to or suspended from the ceiling

Uplighting – free-standing, pendant and wall-mounted luminaires

Localised lighting – low-level general lighting

Uplighting and downlighting – from combined or separate luminaires

Lighting Guide LG3: 1996 – The visual environment for display screen use published by services trade association CIBSE gives further details on the design process and selection of the most appropriate lighting design solutions. It also provides detailed advice on the application of each lighting design technique. Details: 0181-675 521Lighting Industry Federation has set up a VDT Luminaire Registration Scheme for manufacturers, the aim of which is to provide lighting designers with a reliable basis on which to make the correct luminaire selection for workstations. Although there are four types of lighting systems that can provide acceptable lighting conditions for VDT areas, the LIF initiative addresses itself to downlighting luminaires only. Details: 0181-675 5432

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