- Energy saving bulbs

This page is a summary of the information that you might need when choosing your Energy Saving Lightbulb.


There are a multitude of fittings for lightbulbs, but the standard domestic ones generally come in one of five different fittings. There are the bayonet clip fittings (push the bulb into the socket firmly and give it a quarter twist), and the screw fittings (push in the bulb and twist it clockwise until it won't turn any more). Each of the bayonet fitting and the screw fitting come in a large and a small size. Finally there is the two pin (mains voltage) halogen lamp fitting (push in and give a quarter turn clockwise).

Looks like this: Called this: Measures:
BC fitting Bayonet cap, BC, B22d diameter: 22 mm
SBC fitting Small bayonet cap, SBC, B15d diameter: 15 mm
ES fitting Edison Screw, ES, E27 diameter: 27 mm
SES fitting Small Edison Screw, SES, E14 diameter: 14 mm
GU10 fitting GU10 pins 10 mm apart

Power (wattage) conversion table

The main reason for using Energy saving lightbulbs is that they give out the same amount of light as conventional lightbulbs, but use up much less electricity to do so. The table below gives you the conversions* you need to choose the right bulb for your purposes.

Energy saving bulb Incandescent GU10 CFL Halogen
4W = 20W 7W = 30W
5W = 25W 9W = 40W
7W = 35W 11W = 50W
9W = 45W
11W = 60W
15W = 75W
20W = 100W
23W = 125W
30W = 150W
40W = 200W
60W = 300W
80W = 400W
100W = 500W
*Note that the values given above apply to Megaman bulbs. Some of the economy priced products may have lower efficiencies.

Cost of ownership

In the table below we calculate the energy cost of a traditional 60W bulb used for seven hours each day (perhaps as a hall light), and compare it with the cost of an energy saving bulb's electricity usage.

Bulb type Traditional bulb Energy saving bulb
Power consumption 60W 11W
Hours per day used 7 hours 7 hours
Electricity cost (£/KWh) 0.12 0.12
Annual running cost £18.4 £3.37
Savings from Energy saving bulb £15.03

In the example above, the energy saving bulb saves you £15.03 in electricity each year. So as long as the difference in price of the two bulbs is less than this amount, the payback will be less than one year. Furthermore, the life expectancy of an Energy saving bulb is normally between three and eight times as long as a conventional incandescent bulb. This makes the pay back on an energy saving bulb even more attractive. 

Colour temperature

The colour of an Energy Saving Bulb has traditionally been one of the concerns of customers. The days of lamps giving off a cold, harsh light are thankfully over and many of the modern energy saving bulbs have just as warm a colour as conventional incandescent bulbs.

Colour temperature (K) Colour Code Description
2700 827 Very warm white
3000 830 Warm white
3500 835 White
4000 840 Cool white
6000 860 Daylight, cold

Dimmable bulbs

Traditionally, Energy saving bulbs have not been compatible with household dimming circuits. However there are two types of energy saving bulbs that can be dimmed: switch dimmable and dimmerable. Please read the product descriptions carefully to make sure you get one that is compatible with the use you require it for.

Early Dimmable bulbs

The first technology developed that allowed an energy saving bulb to be dimmed is sometimes called switch dimmable. With these, the bulb is switched on until it reaches 100% brightness. To dim, the lamp is switched OFF and then ON again within 3 seconds. The bulb begins to dim. The lamp is then switched OFF and ON again when the bulb is at the desired brightness level.

Dimmerable bulbs

A more modern technology has now been developed that allows Energy Saving bulbs to be used with ordinary wall mounted dimmer switches. They are still not recommended for soft start, digital, slide, or touch dimmers as these can have a high in-rush current. The capacitive load of a dimmerable lamp is different to an incandescent bulb so to work out how many dimmerable lamps you can use you have to divide the maximum rating of the dimmer by 6 (six) to get the amount of CFL power you can use. 

Frequently asked questions

The following questions are posed most frequently to the Energy Saving Trust

Doesn't switching lights on and off use more energy than leaving them running?

No. Switching on an energy saving bulb only uses the same amount of power as leaving it on for a minute or two.

Turning the bulb on and off repeatedly may shorten its life, but normal household use shouldn't cause any problems. However, to help it last as long as possible, it is best to leave it on for a 'stabilising' period of 10 to 15 minutes at a time.

And if you're still using traditional bulbs, remember to switch them off every time you leave a room unoccupied. In the UK alone we waste an incredible £140 million a year by leaving lights on unnecessarily.

Don't energy saving lightbulbs take a long time to light up?

No, most modern energy saving bulbs take little more than a few seconds to warm up to full brightness.

This short warming up process is due to the way they work. An electric current is passed through gas in a tube, making the tube's coating glow brightly. In traditional bulbs, the current is passed through a wire which heats up and produces light straight away. What makes them incredibly inefficient is that 95% of the electricity used is lost in the production of heat.

Energy saving bulbs, by contrast, use the same efficient technology as fluorescent lights - but are more compact and use even less energy.

Producing an energy saving bulb must take more energy in the first place than making a standard bulb. At the end of the day, doesn't that make it inefficient?

Again, no. Because of its clever technology, an energy saving bulb might take more energy to make than a traditional bulb. But the energy saved by the bulb over its lifetime far outweighs this energy consumption.

Don't traditional bulbs give a better quality of light?

For technical reasons, the glass used to house energy saving lightbulbs has to be opaque - not totally transparent. In other words, the light quality of energy saving bulbs can't be directly compared with that of clear traditional bulbs. Compare them with soft tone traditional bulbs, though, and you won't see any difference.

Are halogen bulbs more efficient than traditional bulbs?

Yes, but they are not as energy efficient as normal energy saving bulbs. So, halogen bulbs should only be used in your existing halogen fittings.

Halogen bulbs come in mains voltage (240 volt) and low voltage (12 volt) varieties. Low voltage bulbs use a transformer which takes the voltage from the mains supply and 'transforms' it to the lower operating voltage of the halogen light. This helps them to use less energy and makes them 35% more efficient than traditional halogens.

Is the government really banning traditional incandescent bulbs?

There is a proposal for a voluntary phasing out of traditional bulbs between now and 2011. This will give manufacturers and retailers enough time to develop additional products that will take their place.

Don't CFLs contain mercury? And isn't that bad for the environment?

Energy saving bulbs contain only tiny traces of mercury - imagine a pellet smaller than the tip of a biro. What's more, in the long term, CFL technology will actually help less mercury to pollute the air.

This is because burning fossil fuels like coal is the biggest source of mercury in the air. And as energy saving bulbs use 80% less electricity than a traditional bulb, they mean far less mercury overall.

Remember to always recycle your used bulbs, for example at your local authority's recycling centre.

The National Household Hazardous Waste Forum runs a website with details of these centres for chemicals (which also applies to other hazardous wastes).Visit the National Household Hazardous Waste Forum website and search with your postcode for your local chemical disposal or collection service.