Introduction to Architectural Science: The Basis of Sustainable Design by Szokolay Steven V

Author:Szokolay, Steven V. [Szokolay, Steven V.]
Language: eng
Format: epub
ISBN: 9781317918578
Publisher: Taylor and Francis
Published: 2014-04-10T18:30:00+00:00

Light-coloured tasks with good contrast, with an overall gloss, e.g. pencil on coloured paper or tracing, reading glossy paper

160

Dark-coloured tasks with an overall gloss and light coloured tasks, with poor contrast, e.g. glossy photos, half-tone on glossy paper

800

To avoid the opposite effect, namely surfaces appearing ‘too dark’, the CIBSE* Code for Interior Lighting recommends that in offices, if work-plane illuminance is Ew = 1, then the walls should receive 0.3–0.7 Ew, the ceiling 0.3–0.9 Ew, the floor 0.2–0.4 Ew and the wall containing a window at least 0.6 Ew.

2.5.6 Integration/discussion

In side-lit rooms the level of daylighting rapidly drops with the increase of distance from the window. It often happens that daylighting near the window is quite sufficient, but not at the back of the room. The rear part of the room could be used for storage (e.g. filing cabinets) or visually less demanding functions (e.g. tea-making) but work areas may still be left with inadequate daylight. Probably the full electric lighting system would be switched on. The energy conservation (thus sustainability) requirement would dictate that day-lighting be used whenever and as far as possible.

A simple solution is to arrange the electric lighting in rows parallel with the window wall and switch these rows on only as and when necessary (Fig. 2.66). It is rare to find side-lit spaces where daylight alone would be sufficient beyond a depth of about 2.5 times the window head height (from the work-plane). In this case there may be some permanent electric lighting at the rear of the room, hence the acronym PSALI (permanent supplementary artificial lighting of the interior).

It has been demonstrated that people prefer daylight to artificial light and they do like (perhaps even need) visual contact with the outside world and its continually changing lighting conditions. For all these reasons the principles of PSALI have been established as:

1 utilisation of daylight as far as practicable;

2 use of electric lighting to supplement the daylight in the interior parts of the room;

3 design of the lighting in such a way that the essentially daylit character of the room is retained.

The last of these principles sets a qualitative as well as a quantitative requirement. Warmer light (a lower colour temperature) is acceptable with low levels of illuminance. Here it should be comparable to daylight, which is of a colour temperature of 5000–6500°K. In situations where visual tasks are all important (drawing offices, laboratories) for precision work and good colour rendering, an ‘artificial daylight’ lamp (of 6500K) is advisable. In less critical situations a ‘cool white’ (of 4300°K) is acceptable.

The illuminance provided by the supplementary lighting should be comparable to the quantity of daylight available near the window, at the 2% DF contour. Above this, there would be no supplementary lighting, and below this, we would attempt to bring the illuminance up by artificial light input. The magnitude of this can be estimated as follows:

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