Lighting
Demand: Lighting/1
This worksheet covers
• Amount and type of energy used in Lighting
• CO2 emissions from Lighting
• Reducing energy used in Lighting
How much energy do we use in lighting?
• We use lighting at home, at work, at school and for travelling
•
at night.
The table below shows the estimated electrical energy used for lighting by an average two person home:
Device
Power
Time per day
Energy per day per home
10 incandescent lights
1kW
5 hours
5 kWh
10 low-energy lights
0.1kW
5 hours
0.5 kWh
•
Assuming a mix of light bulb types, the average person’s domestic lighting requirement would be around
2.7kWh per person per day.
•
At work or school, lighting is used in daylight hours and after dark, it is shared between many people, and the
lighting well be more efficient. A rough estimate puts the consumption at half that used at home: 1.3kWh per
day per person.
•
Street lighting amounts to about 0.1 kWh per person per day, and traffic lights even less. Councils may aim to
reduce their energy bills on lighting – but while we use incandescent lights, street lighting remains a small
contribution to our overall lighting energy per person.
•
This gives a total daily demand for lighting of 4kWh per person per day.
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Lighting
What does this energy use amount to in terms of CO2 emissions?
Using 1 kWh of electrical energy in the UK is roughly equivalent to releasing 0.5kg of CO2. This means
4kWh/day/person is equivalent to releasing 2kg of CO2/person/day.
How can we reduce this?
There are two main ways of reducing the energy consumed in lighting
• Reducing the lighting demand – using natural light wherever possible,
and turning the lights off when not needed!
• Making lights more efficient – using energy efficient bulbs / sodium
lights instead of incandescent bulbs
Changes like these can reduce the energy consumption in lighting by 55%,
which means the average use for a UK person would then be 1.8kWh/day:
a significant saving.
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Lighting
The economics of low energy bulbs?
It seems counter-intuitive to throw away a fully functioning bulb!
This though is exactly what you should do – the following analysis
will show why:
• A modern low energy light bulb consumes 20W and is claimed to
give the same illumination as a conventional 100W incandescent bulb.
• The lifetime of the low energy bulb is quoted as 15,000 hours; for an
incandescent bulb it is around 1,000 hours. So for the same time period
you would need 15 incandescent bulbs for a single low energy bulb.
• For the 15,000 hours of operation the low energy bulb will use 300kWh of energy; the incandescent bulbs will use
1,500 kWh. A kWh of electricity is roughly 12p, therefore operating costs for the low energy bulb are £36, for the
incandescent bulb £180.
• The purchase price of an energy saving bulb is now roughly comparable to that of an incandescent bulb – but you’d
need to buy many more incandescent bulbs over the lifetime. Leaving this aside, the running costs alone make the
decision simple: by changing to a low energy bulb you could save around £144 over the lifetime of the bulb
compared to the incandescent bulbs.
Sources
MacKay DJC, Sustainable Energy – without the hot air, UIT Cambridge, 2009.
Also available free online from www.withouthotair.com
Light bulb information from www.Lightbulbs-Direct.com