The Lighting of Drawing Offices
The British Building Research Station has recently undertaken a survey of drawing offices in order to ascertain the needs and views of users in matters such as lighting, furniture layout and equipment. In this Digest the opport unity is taken to consider the lighting requirements in relation to basic principles and the results of the survey, and to suggest ways in which good lighting can be readily and economically achieved.
Lighting, however, is only one of the many factors to be taken into account in the design of drawing offices. The survey showed quite clearly that good ventilation and adequate space were at least of equal importance. A later Digest will deal with the problem of space and layout.
BASIC PRINCIPLES
DIGEST 70 (first series) dealt with
some of the principles of good lighting. By good lighting is meant lighting that enables a task to be performed with maximum efficiency. stimulation and visual comfort, and with a minimum amount of fatigue. Digests 80 and 81 (first series) went on to show how lighting could be designed in accordance with these principles. The present Digest is intended to show how these prin- ciples can be applied to the particular case of drawing offices.
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With the exception of tracing, daughtsman's work does not, in gen- eral make unduly high demands on his vision for long periods. In fact, stu- dies made during the survey showed that, on average, less than one-third of a draughtsman's time is actually spent on drawing, about the same proportion being spent away from the drawing board altogether. On the other hand,
he is engaged for the greater part of the day on work that is visually more exacting than general office work. This work requires a high degree of concen- tration, often in the presence of much distraction, especially when he is work- ing in a large, open office. The fact that only a part of his time is spent on actual drawing in no
way lessens the importance of providing the best form of lighting possible. Rather does it point to the need for an environ- ment designed to suit a number of ad- ditional activities, such as consultation of reference material, filing, confer- ences and so on, which might take p'ace in all parts of the office.
The lighting therefore has to be de- signed to satisfy the following require-
ments:
It must light the work adequately It must help the draughtsman to concentrate on his work without dis- traction and fatigue
It must be designed to allow for work other than drawing.
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An important first principle of good lighting is that the areas where the more exacting work is done in this case the parts of the drawing on which the draughtsman is working should appear brighter than anything else within his immediate field of view. One way of ensuring this is to light the work preferentially. A particular ad- vantage of accentuating the work in this way is that it enables the draughts- man to concentrate with less strain amid the distractions always present in a large office.
Nevertheless, the contrast in bright- ness between the work and the sur- rounding surfaces must not be so great as to cause visual discomfort. There should be a gradual reduction in bright- ness from the work itself, through the immediate surroundings towards that of the general environment that is, the room forming the background to the drawing board. The most import- ant surfaces here will be the floor, other furniture and the walls. Atten- tion to the choice of reflectances of the surfaces and to the level of general lighting will meet this particular reed. As a working rule, the brightness of the surfaces should be of the order of one-tenth of that of the work.
In practice, the graduation will often be interrupted by competing areas of high brightness. It is usually practic- able to screen excessively bright views of the sky, and to reduce excessive con- trasts by painting reveals, frames and immediate surrounds of windows or roof-lights white or in light colours. Artificial light fittings should be so de- signed that their surface brightness is kept within certain prescribed limits, and that they throw a portion of their light on the surrounding ceiling. It is not usually practicable to make them less bright than the work itself, nor is it entirely desirable, for if they are too dull they make the surroundings ap- pear gloomy.
THE HONG KONG & FAR EAST BUILDER_VOLUME 17, NUMBER 2
DAYLIGHT
Draughtsmen carry out a high pro- portion of their work during the hours of daylight and most of them declare а preference for working in daylight rather than in any other form of illumination.. To give satisfaction, however, the daylight must be distri- buted evenly throughout the office: otherwise, staff working at the drawing boards some distance from the windows will feel deprived of light.
It is therefore essential not only to plan for an adequate amount of day- light but also to distribute it evenly over the working area. In fact, the survey confirm that the distribution of daylight ranks equally with considera- tions as
Further- to its sufficiency. more, the daylight should reach the working plane from a wide angle. For instance, it must not come from small windows at one side or it will throw hard shadows.
It is these problems of distribution which should govern design decisions about the width of offices, the position- ing and size of windows and the need for roof lighting.
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A daylight factor of 5% is generally regarded as an appropriate minimum ratio for drawing offices, and the sur- vey confirms that this is a figure that enables the majority of occupants to work at their boards without resorting tc artificial light. In practice, minimum daylight factor of 5% is dif- ficult to achieve in rooms wide enough to accommodate more than two rows of drawing boards, unless the room is lit from windows on opposing sides or roof lights are installed. Attempts to raise the daylight factor in the centre of wide rooms by providing exception- ally large windows are not likely to be successful because draughtsmen work- ing in the centre of the room may have bright areas in their field of view pro- ducing unpleasantly high contrasts with their immediate environment.
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