Please attribute this one to Pete Hart, Technical Director UK!

Easy as Divide by Five and Multiply by Ten!

Q. Packaging information on lamps has changed recently and many buyers are finding the new information confusing.

I understand light output is not measured in Watts so is there any way I can easily remember which lamps to purchase using low energy lighting numbers and not the old format of 60W, 100W etc.?

A. Conventional GLS lamps were rated by Wattage and every buyer or user could easily associate the lamp “Brightness” with its power. However, with Europe phasing out incandescent and tungsten halogen lamps, low energy alternatives are being introduced which are completely different in operation from the “Hot wire” filament lamps.

The different technology used to make compact fluorescent lamps (CFL) and LED light sources means that the amount of light they produce per Watt is far higher than the old GLS lamps. This in turn means that we need to describe a lamp’s performance in comparable terms, in this case as ‘light output’ or Lumens.

The lumen output of a lamp tells the end user exactly how much light it produces rather than how much power it consumes (although the Wattage will still be shown on the lamp and packaging).

More importantly, the ability of the lamp to produce light efficiently is easily calculated as lumens per Watt. As a general rule of thumb, CFL lamps are about five times more efficient than GLS and last ten times longer.

There are two simple rules to remember:

Divide by Five: If we used a 100W GLS in a living room ceiling light, it can be replaced with a CFL lamp of around 20W to produce a similar amount of light within the room.

Multiply by Ten: When buying low energy lamps, remember they last around ten times longer than GLS.


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