SJE Electrical Installations:
Lighting Techniques:
Types of fittings. Fittings should be chosen according to their
qualities in the following respects: appearance; light distribution; brightness;
ease of erection, relamping and cleaning; cost; and luminous efficacy. The order
of importance changes with different applications, but light distribution should
always be considered first.
Fittings classed 'mainly direct' give most of their light in one direction. With
any given type of lamp they will give the highest luminance per watt of
electrical input, with some likelihood of glare either direct from the lamp or
by reflection from polished working surfaces, with a tendency to hard and deep
shadows, but with the possibility of ensuring that at any particular working
position most of the light comes from the desired direction as may be required
in say a drawing office.
Direct lighting is almost always used for industry and for display purposes in
shops; it gives a brisk, lively effect which emphasizes light and shade and
reveals shape well.
Indirect lighting is usually considered more restful and is used
mainly for restaurants, hotels and other social interiors, and in
combination with direct lighting for many classes of shops
although it is becoming increasingly popular for office lighting
using so-called 'uplights' fitted with SON-DL or MBIF lamps.
'General diffusing' lighting, or 'direct' is generally used in offices and
schools.
Spacing of fittings. In most interiors which contain several lighting fittings
the aim is usually to provide general lighting, a comparatively even
illumination at working level all over the room. This allows furniture and plant
to be moved and added to without altering the lighting installation. Too wide a
spacing of fittings would give the effect of comparative darkness between pools
of light, whereas an unnecessary close spacing would be uneconomic.
As a general rule, applying both to fluorescent lamp fitting and other types
normally used for general lighting, a satisfactory even illumination results
when the fittings are not spaced more than 1 x times their distance above the
plane of work, with end fittings half the distance from the wall, or one-third,
if work is done next to the wall.
Floodlighting Techniques
This form of outdoor illumination has three main applications, (a) for
industrial purposes, (b) for decorative purposes, and (c) outdoor sports
Industrial floodlighting. High-pressure discharge lamps are suitable for this
type of application. The SON lamp for example, is commonly used area
floodlighting and SON.TD or MBIL/H or lamps used in accurately designed
parabolic reflectors are also used for long distance floodlighting.
Decorative Floodlighting. It is necessary in this application first to decide
upon the average illumination required. This naturally depends on the reflection
factor, which depends on the texture of the surface and whether it is clean or
dirty. For clean Portland stone the factor is 60%, which is reduced to 20% if
the surface is dirty. On the other end of the scale clean red brick has a
reflection factor of 25%, dropping to 8% if dirty.
The question of arranging the projectors requires careful consideration.
Lighting directly from the front is seldom satisfactory, while lighting from an
angle can be most pleasing. Lighting of polished surfaces is seldom successful
using floodlights, as they tend to act as plane mirrors, producing an image of
the floodlight.
One technique is to light objects in front of the polished surface so that it
stands out in silhouette.
Sports grounds. Practice or casual training areas can be lit from one side by
using tungsten halogen lamps, mounted on 3-5 metre poles but tournament areas
require a higher luminance and more rigorous glare control. Minimum mounting
heights of 10 metres are recommended and the area should be lit from both sides.
Stadiums are lit to a higher standard. The most popular method is to light the
area by means of 1000W SON or similar, deluxe lamps mounted on towers up to 30
metres high.
