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Low energy lighting


The past few years have seen a huge upheaval in how we light our homes and offices. The traditional incandescent lightbulb is no longer on the shelves of shops. They were very inefficient. 90% of the electricity used to light incandescents was lost in the form of heat. Halogen light bulbs – a much smaller version of incandescents – also generate a lot of heat. They use less electricity than incandescents, but tend to be used in greater numbers, which cancels out the savings.

Changes to regulations have triggered a step change in developments in the lighting industry. It is now possible to find a great variety of Compact Fluorescent Lamps (CFL) and Light Emitting Diodes (LEDs). The teething problems with brightness, colour and range of shapes are being ironed out, and performance is rapidly improving. However, you do need to think about more things than you did when it was just a choice between 40, 60 or 100w incandescents.

Comparative costs

Comparative cost of lamps

Comparative cost of lamps

You probably know that halogens are cheaper to buy, and more expensive to run than LEDs and CFLs, but do you know how great that difference is?

LEDs are three and a half times more expensive to buy, than halogen lamps. However, Halogen light bulbs cost 19 times as much to run for a year. So you can start saving money on your electricity bills five months after installing them (depending on how many hours a day the lights are on). CFLs are two and a half times as expensive, and four and a half times cheaper to run.

Bulb life is also an issue. Halogens last for just 1,000 hours of burn time. CFLs will light up for 10,000 hours, and LEDs double that.

As a result, the cost of lighting with halogens can be as much as 20 times as much per year as the cost of lighting with LEDs. Click on the picture to enlarge, and see the detail.

How to choose the right lamp

Traditionally we've measured the strength of our lightbulbs (lamps) in watts. A 40 watt incandescent light bulb was dim, a 100 watt one was bright. However, that measure was misleading. Watts are a measure of power consumption, not of light.

A 100 watt incandescent bulb needed 100 watts of electricity to light it. As a result it was brighter than a 40 watt bulb. To get the best low energy lighting, we need to know more. The goal is to get the right brightness, for the lowest energy use. So this is a guide to the measures you need to be aware of when you buy low energy lights.

Lumens are a measure of the light given out by a lamp. The higher the lumens, the brighter the lamp. A traditional 40 watt bulb gave out around 450 lumens. As a general guide:
Incandescent lamps give out 10-12 lumens per watt
Compact fluorescent lamps (CFL) give out 50-60 lum/w
Light emitting diodes (LED) give out 40-90 lum/w

LEDs are increasing in performance at an incredible rate. Two years ago you could get 25-30 lumens per watt. Now they are generating between 65 and 100 lumens per watt. Performance is expected to go on improving.

Colour temperature:
The colour of light is measured in degrees Kelvin. The colour is what results in us perceiving light as warm or cold; harsh or soft. Cold light will have more blue in it and warm white has more yellow.
Daylight is 5,000 Kelvin
Cool white is 4,200k
Warm white is 2,700k
In the UK, most lamps are between 2,700k and 3,500k.

We suggest you test one bulb to make sure you're happy with the light it gives before investing in larger quantities. Some local community groups have light bulb libraries, which they lend out so people can try before they buy. We replaced halogens with 3,000k LEDs, and they seem warmer.

There is another colour measurement, the colour rendering index or CRI. This measures the quality of a light source compared with sunlight. Sunlight is given the maximum CRI value of 100. The closer a lamp is to that, the better its ability to show true colours. This is important in art galleries and shops, but is not critical for optimal light levels in homes. Lamps for domestic use can have a CRI level as low as 60 (which means they are less expensive to produce and buy).

Energy use:

On the packaging this is measured in two ways. There will be a number of watts. This tells you how many watts are needed to power the lamp. The lower the number, the better for your purse. There may also be an energy rating, where A is the best, and G is the worst.

How to change a lightbulb!

There are two key issues to take into consideration:

Most low energy lightbulbs do not work with dimmer switch circuits yet. There are dimmable LEDs, but they cost much more (between £20 and £45 each compared with £7 to £9 for standard LEDs), and there is a growing range of dimmable CFLs. Another option is to use ‘staged dimming’. This gives you an option of high, low or off. Alternatively you could get an electrician to change your dimmer switch to a simple on/off one.

Halogen to LEDs

There are two types of Halogen lights. GU10s which run on 240 volts, and MR16  fittings, which are 12v and need a transformer. The latter have two pins as a fitting, the former

For GU10 fittings (240v) it should be fine to simply replace the halogen lamp with a LED. The early LEDs did have a problem with overheating, but the latest ones shouldn't.

MR16 fittings are more complicated. Whether a straight swap will work will depend on the rating of the transformer. If it is rated from 0+, then it's OK. If, say, it's rated from 50w - 100w, then it won't detect the 3w LEDs and will keep tripping out.  As the lights are often recessed into the ceiling, it may not be easy to find the transformer and look to see what its rating is.

We replaced four halogens in our bathroom with LEDs. Three are working fine. The fourth flickered enough to be quite annoying.

Incandescents to CFLs

It is very simple to make this change. CFLs are now available in a wide range of shapes, sizes and fittings.

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