the
In the course of the survey many comments were made about the need for sun-blinds or window curtains, often by people seated well
away from windows. This criticism of large win- dows is particularly valid if the horizon is completely unobstructed, for instance, in drawing offices on the upper floors of tall buildings.
For large wide offices, roof lighting in some form is essential to provide the required minimum level of daylight in the centre of the room. This can be arranged in single-storey offices or draw- ing offices on the top floor of multi- storey buildings; unless north-lights are used, however, screens, louvres or other means may be required to protect draughtsmen against discomfort from sunlight. In large offices where roof lighting is impracticable, the per- manent supplementation of daylight by artificial light should be considered. Digest 135 (first series) reviews the gen- eral principles of this method, the basic design requirement being to obtain satisfactory balance between daylight and the artificial light.
a
Total artificial light is unsatisfactory for a drawing office. Some windows should always be provided, if only to establish a link with outside this re- mains true even where daylight is pro- vided from overhead.
From the foregoing, the following practical considerations emerge :
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(1) Windows and roof lights should be designed to provide as nearly as possible an even distribution of daylight throughout the whole
room.
(2) The design should be based on a minimum daylight factor of 5% and, if necessary, windows should be supplemented by suitably screened roof-lights or by the permanent use of specially de- signed artificial lighting.
(3) It is desirable to provide blinds, curtains or louvres to screen views of excessively bright areas of sky and to control the entry of sun- light. Some form of light-coloured blind or screen will in any case needed at night to eliminate dark areas of window in the field of view and to improve the distri- bution of light within the room. (4) The brightness contrasts around
windows and roof-lights should be reduced by using light colours on the frames, reveals and the sur- rounding surfaces.
as
(5) Piers or columns between ad-
jacent windows should be circumstances permit, to avoid uneven lighting and patches of shadow.
(6) The window frames and the in- termediate members should be slender, so as to reduce the con- trast between them and the sky.
(7) Ceiling, floor and furniture should be as light as possible to soften shadows and provide the maxi- mum diffusion of light.
ARTIFICIAL LIGHTING
lighting
An artificial
installation must satisfy the same basic require- ments as those for daylighting. The achievement of a satisfactory distribu- tion of light presents no special pro- blems, because fittings may be dispersed later, there are other considerations such as the brightness relationships, the brightness of individual fittings and the avoidance of glare, which become cri- tical when high levels of illumination are required.
In selecting the most suitable light- ing scheme for a particular office, three of the questions to be answered are as follows:
Is the general lighting to be supple- mented by local lamps at each draw- ing board?
Should incandescent ог fluorescent lamps be used?
What level of illumination is desir- able?
General lighting v. local lamps
The traditional way of bringing en- ough light on to the working area and of eliminating unwanted shadows is to use a 'local' adjustable lamp.
This provides а scheme under which draughtsmen can work with reasonable efficiency and comfort, and many an unsatisfactory general lighting scheme has been improved in this way. How- ever, local lamps should not be used as an excuse for poor design of the gen- eral lighting scheme and the best results can only be achieved when the general lighting is adequate. With the development of extended sources and lighting systems which employ the en- tire ceiling as a light source, many of the difficulties of achieving а high illumination without glare and without shadows can be overcome without us- ing local lamps, so avoiding wiring to board positions and the untidy appear- ance of a multiplicity of lamp arms. However, unless such schemes are de signed with particular attention to the distribution of luminance (i.e., bright- ness) in the field of view, as well as to the directional qualities of the light, they may still leave much to be desir- ed. Furthermore, a high level general lighting scheme tends to be harsher and less intimate in character than general installations plus local lighting; also it cannot be controlled by individual draughtsmen and if badly designed places him in a frustrating environment.
On balance, therefore, there is much to be said in favour of schemes incor- porating local adjustable lamps. Good general lighting plus local lighting is in more direct accord with the basic prin-
ciples of lighting and vision; in addi tion, draughtsmen have some
control over their surroundings. They can make adjustments to their lighting and eliminate awkward shadows, and they have a better chance of combating dis tractions from work going on elsewhere and can
concentrate on the
work in hand. The survey indicated that the general lighting schemes without local lighting were not more popular than local lighting, even though the overall environment was illuminatetd to higher level.
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One difficulty which can arise with lamps mounted on the board is that they can be left in such positions as to cause glare to draughtsmen working at boards nearby. It is desirable there- fore to have a lamp with restricted movement and a deep reflector.
Where attempts have been made to imitate the effects of local lighting by placing general lighting fittings direct- ly over the working position, the re- sults have been unsatisfactory, for such a design is unlikely to result in a suit- able brightness distribution over the whole room. Apart from this, where adjustable local lamps are not provid ed, the light at any one point must come from a number of overhead fittings in order to prevent hard shadows.
Incandescent or fluorescent lighting
With fluorescent lighting installations using up-to-date lamps and control gear, there are fewer complaints than there used to be about such things as multiple shadows,
flicker and unplea- sant colour renderings. The survey confirmed that, in general, the main at- titude of draughtsmen to fluorescent lighting is favourable; in offices where it is installed, over 70% registered ap proval with or without further quali fications.
An analysis of the main ar- guments for and against fluorescent lighting showed the most frequently mentioned point in its favour to br evenness of distribution and the most common objections to concern glare. Fears about discomfort from flicker were express mainly by non-users, which suggests that this trouble is an ticipated rather than experienced and may be based on experience of out-of- date installations.
The
survey confirmed that
on the whole there are no serious reasons why fluorescent lighting should not be used for the general illumination of drawing offices. The following points should be borne in mind, however.
The installation must be designed to eliminate the possibility of annoyance from flicker, which could give rise to serious complaints. Practical precau- tions include adequate screening of the ends of the lamps, and, where the level of illumination is very high, the use of twin-tube fittings with adjacent lamps (See Page 86)
THE HONG KONG & FAR EAST BUILDER-VOLUME 17, NUMBER 2