Guidebook for Energy Efficiency in Municipalities

The following list informs about the most appropriate lamp type for most applications.
- For many general applications: Modern fluorescent lamps, especially the more efficient
‘tri-phosphor’ lamps, have low cost, high efficiency, good colour (unlike the blue hues
of older lamps) and very long life (8,000-16,000 hours rated life compared with 1,000-
2,000 for incandescent lamps). They are readily available in lengths of 300-1500 mm.
- For situations where there are size or style constraints: Compact fluorescent lamps
have characteristics similar to full-sized fluorescent lamps but are suitable for
applications where the size or appearance of normal fluorescents is unacceptable or
the high lighting output is unnecessary (e.g. desk lights, downlights, wall washers).
- For lighting large areas (e.g. indoor pools, depot garages): Metal halide lamps produce
a crisp white light. They have efficiency about the same as the best fluorescent lamps
but more light output, and so fewer fittings are needed.
- For situations of infrequent use: Incandescent lamps (including standard light ‘bulbs’,
low-voltage and linear tungsten halogen lights) should only be used in fittings which
will be operated for less than 500 hours per year, such as cleaners’ rooms, or outside
lights controlled by movement detectors.
Apart from lower energy consumption, energy-efficient light sources such as fluorescents
have two significant benefits, namely increased reliability (and hence safety) and reduced
maintenance costs (both lamps and labour). Low-voltage lighting is over-used in many
office buildings, partly because of the misconception that it is energy-efficient. Its real
advantages are:
- the ability to highlight a small area or object (e.g. a painting); and
- small size, which can be an issue in some lighting installations.
However, energy efficiency is not one of them, since low-voltage lights are not low-power
or low-energy ones. Their efficacy is about 20 lumens per watt (compared with 90-110
lumens per watt for modern fluorescent lighting). The transformers supplying the lowvoltage
power also use energy (typically 10-20 watts per lamp) further reducing the
efficiency of the lighting system, and this should be taken into account when calculating
the energy use of low-voltage lighting systems. Low-voltage lighting should not be used
for lighting large areas, such as entire foyers and reception areas.
Role of the fitting
A light fitting (or ‘luminaire’) should distribute the light produced by the lamp as efficiently
as possible to where it is required, while minimising the total cost over the life of the unit
(purchase price plus energy, maintenance and other operating costs). Some perform
better than others do, as an efficient fitting can use half the power of an inefficient one to
produce the same light output (even though they may both use the same kind of lamp).
Traditional recessed fluorescent lamp fittings with acrylic plastic diffusers deliver about
50% of the light produced by the lamps into the room, while the best models, which
incorporate carefully shaped reflectors, deliver more than 75% of the light produced.
Fluorescent fittings include a device called ‘ballast’, which controls lamp current. This
unseen component consumes up to 10 watts per lamp, or more than a quarter of the
power rating of the lamp itself. Modern electronic ballasts are available which:
reduce the total power of the light fitting by about 25% while maintaining light output
(compared with only an 8% reduction with ‘low-loss’ iron-core ballasts);
eliminate flicker during start-up and normal operation; and
extend lamp life.
‘Low-loss’ iron-core ballasts reduce electrical power by about 3 watts per lamp (reducing
ballast energy use by one third compared with a standard ballast). Although the savings
are much lower than those of an electronic ballast, they are suitable for the replacement