Lighting is taken for granted in industrial countries. It
is hard for many people to imagine living at night
without being able to obtain light at the flick of a
switch. But grid electricity does not extend to many
rural areas in developing countries and is not likely to
be in the near future, and even in for many urban
households people have difficulty accessing clean
energy sources as they are not connected to the grid or
have unreliable power supplies.
Lighting in the rural areas of developing countries is
often provided by candles or kerosene lamps. To a
lesser extent, biogas, diesel generators and renewable
energy systems are used. Torches (or flash-lights)
powered by expensive, disposable dry-cells are used as
a portable source of light for intermittent use. Access
to modern energy products is hindered by poor market-
supply chains, low awareness of existing technologies
and lack of access to finance for consumers and
Figure 1: Low energy lamps help with
Photo: Practical Action Nepal.
What is light?
Light is electromagnetic radiation; the human eye is sensitive to a spectrum with visible colours
as seen in a rainbow. When these colours are mixed they appear as white light. More energy is
present in the violet/blue end of the spectrum than at the red end. Therefore, more energy is
generally necessary to produce the blue-violet component needed to produce what to the eye
appears as white light. So the quality of light (in colour terms) influences the energy
requirement; if colour does not matter then it is at least theoretically more efficient to use a red
or orange light, and this in fact is common practice in the case of street lighting where energy-
efficient lights are used, namely orange/yellow sodium lights. For domestic purposes people prefer
to pay extra to get white or near-white light.
Light intensity, or illuminating power of a light source in any one direction is commonly defined in
candela, which although it has a rigorous scientific definition, for practical purposes can be
thought of as 'candle-power'; i.e. the output from a standard paraffin-wax candle. The rate at
which light is emitted is measured in lumens, which are defined as the rate of flow of light from a
light source of one candela through a solid angle of one steradian. A more easily understood
approximation of this would be to imagine a one candela candle at the apex of a conical
lampshade with its sides sloping at about 70 degrees to each other; the conical beam emitted,
diverging at about 70 degrees lighting an area of 1m2, would be about one lumen. Lamps are
often rated in lumens. Another unit measuring lighting is the lux which is used where the area to
be lit is accounted for. When measuring the light intensity in a room rather than the power of a
lamp the lux can be used.
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