The difference between properties with low energy bulbs and those with ordinary bulbs is small with the former only having a slightly better energy rating. After coming to this conclusion, Domestic Energy Assessors, Belfast, Northern Ireland, who survey houses assessing them for an Energy Performance Certificate, decided that, even so, it is worth investing in energy saing bulbs when looking at long term solutions. The following article explains the reasoning behind this.

How they work

Energy saving light bulbs and ordinary light bulbs are fundamentally very different. The former is what is known as a compact fluorescent lamp (CFL) whereas the latter is what is known as an incandescent lamp. They both produce light, but in different ways. In an incandescent lamp, there is a wire filament through which the electric current flows; this heats the filament and makes it glow, giving off light. However, a CFL contains a tube with an inner fluorescent coating called phosphor, and in the tube there is some argon gas and a small amount of mercury vapour. The electric current is driven through this tube and generates ultraviolet light which can’t be seen by the naked eye, and this excites the phosphor which emits light. Initially when they are first switched on CFLs uses more energy, but after time they use around less than 70% energy than incandescent bulbs.

Environmental impact of energy saving lights

The contribution to the carbon dioxide levels in the atmosphere is less for low energy light bulbs because they use so much less power. An amazing statistic that can be used in favour of these bulbs is that each one will save around 2000 times its own weight in carbon dioxide emissions over its lifetime; the lifetime is around 5 to 8 years.

As a result of the improvement in technology over the years, there are many different types of low energy bulbs that can be bought. These include down lighters and ones that fit into spotlight fittings. The trend for using multiple incandescent bulbs as spotlights in the ceiling is very attractive, but also very power hungry. By replacing 10 spotlight bulbs each of 60 W with 10 energy saving bulbs of 9 W, the whole room will be lit up by 90 W rather than 600 W, an incredible saving in energy.

Technical issues to consider

Disposing of energy saving bulbs in a responsible way is important just as it is for ordinary bulbs. Both have a small amount of mercury in them and so must be disposed of very carefully. Discarded bulbs of either type must not be put into landfill but should be recycled. In Belfast, Northern Ireland, recycling facilities exist for items such as light bulbs. This will be at a local tip, in a designated bin. The mercury will be removed from each bulb and reused.


Obviously the cost or replacing ordinary bulbs with energy saving bulbs will vary depending on the size of the house and the number of rooms it has. It will also depend on whether low energy bulbs or low energy spotlights are being purchased. The owner can expect to pay £1 to £2 for each energy saving bulb and £3 to £5 for each low energy spotlight.

Impact on Energy Performance Certificate

The impact on the Energy Performance Certificate of having low energy light bulbs equates to having an additional 1 to 3 points in the energy rating compared to a property with ordinary bulbs which is similar in size, style and age.