Energy Efficient Lighting

Changing a home's lighting from incandescent bulbs to the "energy efficient" variety is a quick win for cost reduction and reducing carbon footprint.  "Energy efficient lighting", is also known as compact fluorescent lighting or CFL for short.  Homes will have between 10 to 40 light bulbs, if these are all of the incandescent variety, they will be consuming between 3 and 10 kWh/day of electrical energy (subjective estimates).  Replacing these with CFL can reduce this to 0.5 to 2 kWh/day.  The cost and C02 reductions, for the sample home are shown in the table below:

	Incandescent	CFL
Number of bulbs	18	18
Average Cost/bulb	£1.50	£0.30
Average life of bulb (hours)	1,000	6,000-10,000
Installed Capacity (kW)	1.40	0.33
Annual Consumption (kWh)	2555	511
Annual Energy Cost (£0.08/kWh)	£204.00	£40.80
Annual CO2 emissions (0.45kg/kWh)	1150kg	230kg

In CFLs electrons are made to collide and thus emitting photons, unlike incandescent bulbs, most of the energy is converted to visible light.  An incandescent bulb might be described as a small electric fire that also gives off light.  Because CFL's operate at much lower temperatures than incandescent ones, their life is 5 to 10 times longer.

Whilst changing to energy saving bulbs will reduce electrical consumption, there are some other factors that should be taken into account.  Until relatively recently, CFLs where slow to start and dull once started, the current generation are much improved.

Startup Time

The CFLs can take up to 30 seconds to achieve full light output.  This becomes an attractive feature on dark mornings, giving one's eyes a gentle transition from dark to light.

Colour

Most modern CFLs produce the "warm white" light of good incandescent bulbs and there is no great effect on the perceived colours of the room.  However, if bulbs have been chosen for their colour properties, some research may be needed to determine if this will change the colour scheme within a room.

Dimmers

CFLs do not work with dimmers.

Price

The price of CFLs varies considerably as does the nature of the stock within retail outlets.  A reasonable guide price would be £1.50/bulb (11 or 20 watt).  The author as installed bulbs with prices in the range £0.40 to £7.50, with no obvious differences.

Size and Style

There are two generic styles of CFL, those which look like a strip light posing as a cactus and others which look like incandescent bulbs.  What you install  is largely a matter of taste.  However, CFL's can be either longer or wider than the incandescent ones they are replacing.  Thus it might be necessary to adapt the light fitting or seek out a specialist design.  It is ironic that some incandescent bulbs are shaped to look like the candles they replaced, some CFL's are trying to look like the technology they are replacing.  Live dangerously and embrace the new.

Doctrine of Unforeseen Consequences

Whilst reducing the energy used to light the house is a "good" thing, it also reduces heat energy into the rooms being lit.  In most situations this will have no noticeable effect on room temperature.  However, a room with two 100w incandescent bulbs effectively has a small electric fire.  There may be cases where the drop in heat energy has some unforeseen effect, say in a greenhouse where the heat energy from the lighting is adequate to maintain the air temperature above freezing and thus prevent frost damage.

Page Updated: 30-Jun-06

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