How to choose the best low energy lighting
Posted by Cathy Debenham on 9 May 2012 at 9:14 am
Traditionally we've measured the strength of our lightbulbs 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 fomr 40-90 lum/w
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.
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).
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 will also be an energy rating, where A is the best, and G is the worst.
See also this blog about comparative costs of lighting
If you have a question about anything in the above blog, please ask it in the comments section below.
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