Lighting accounts for between a third and a half of the energy use in
commercial buildings and significant savings in energy can be obtained
where the positive use of daylight has been planned; associated with
control systems, by means of ‘daylight linking’, natural light provides the
major light source during the day with variable artificial light as back-up.
It will be found that in many of the Case Studies mentioned later in the
book, daylight has provided the necessary amount of light for large parts
of the building during the day, whilst providing the interior space with
an overall impression of daylight, even in areas where the actual daylight
factors may be relatively low, allowing light from artificial sources to be
reduced, with consequent savings in energy.
ARTIFICIAL LIGHT
All forms of energy use in buildings should be analysed, related to the
different needs of individual architectural programmes, to see where
savings can be made; for example in homes, the use of the natural source
has always been paramount during the day, so few savings can be made.
At night however, developments in lamp technology have produced
significantly more efficient artificial light sources and this is an area
where, due to the large quantity of residential property, significant
savings have yet to be made; moreover major energy savings in the home
are to be found in the means of heating and insulation. Table 4.1
illustrates the different aspects of the main types of lamp, providing
comparisons to assist the architect in making his choice. The different
factors identified are those of efficacy, lamp life and colour, but other
factors that must also be considered are those of cost and control.
It can be seen from the column under ‘Lamp efficiency’ that the
favourite domestic lamp – Incandescent Tungsten – has an efficiency of
only 7–14 Lm/watt, whilst the compact fluorescent (CFC) has an
efficiency of between 40–87 Lm/watt. At present the CFC lamps cannot
be dimmed economically, but there are many areas in homes, where
dimming is not a requirement, and with satisfactory colour (2700 K) there
is no reason not to take advantage of their long life and lower wattage.
The newer generation of lower-energy lamps such as the compact and
T-5 linear fluorescent lamps can in many cases replace less efficient
incandescent sources, which can be four to eight times more efficient;
they can also have more than eight times longer lamp life. Used in
conjunction with high frequency electronic control gear further reduc-
tions of 20 per cent in power consumption or energy savings can be
made.
To realize these gains they must relate not only to the lamp, but also to
matching this with the the correct luminaire or light fitting. It is no use
simply fitting energy-efficient lamps into inappropriate luminaires,
resulting in unsatisfactory installations; furthermore an energy efficient
scheme demands regular, consistent and informed maintenance. It may
also be cost effective in large installations to operate a system of ‘bulk
replacement’ of lamps after a specific period irrespective of how many
lamps may have failed.
In buildings for industrial use, no doubt savings may be possible in a
rigorous investigation of the plant required to run industrial processes;
but the area most likely to result in the greatest savings is in building
services, and the greatest of these will be in the lighting, where daylight is
the key.
38 Daylighting: Natural Light in Architecture