Not so very long ago, when incandescent bulbs ruled the roost, choosing the right light bulb based on brightness was incredibly simple, as it was all done in watts. And what’s a watt? Well it’s a measure of energy transfer (named after James Watt, the pioneer of steam engines), but that was always irrelevant. For years, everyone knew that 60 watts meant standard room lighting, 40 watts was a bit dingy, 100 watts was nice and bright for kitchens and bathrooms, and anything brighter than that was best left for surgeons and interrogators.
Getting rid of confusion
Everything’s changed now though, with the decline of incandescent bulbs and the rise of energy-saving and LED bulbs. All of a sudden, the wattage has changed drastically while the brightness has stayed the same, leading to a good deal of confusion. When energy-saving bulbs were first introduced, manufacturers initially dealt with this by printing the wattage the bulb was equivalent to on the packaging, e.g. ‘11w – 60w equivalent’. You can find a table of the more common equivalents at the bottom of the page, which is a reasonably good guide to the likely brightness level of your bulbs (not all energy-saving bulbs give off quite the same light, but then neither did incandescents). However this isn’t the whole story.
While it’s easy to make a rough comparison between incandescent and energy-saving bulbs, lighting is not just about these two types of bulb any more. There are also now various different types of LED bulb, not to mention halogen bulbs, and assorted tubes, so it’s virtually impossible to find a measure of energy that can be applied to all bulbs and still mean anything to the layman. Which is where lumens (lm) come in.
What is a lumen?
A lumen is a measure of the light given off by any light source that can be perceived by the human eye (i.e. not including the invisible wavelengths). Lumens basically cuts out any measurement of how much energy it takes to produce a given amount of light, and just measures the light given off. This is like your car’s speedometer measuring how fast you’re going, rather than the amount of energy it takes to get you to that speed, and is a far more sensible way of defining light levels.
You’ll need to get used to Lumens too, as EU legislation now states that the lumen value of a particular bulb must be printed most prominently on packaging. It’s not hard to see watts and equivalent wattages going the way of pounds, ounces and the dodo in the fullness of time. So how do lumens work then?
As a rule of thumb, lumens are very roughly equivalent to the incandescent wattage times ten, plus a little bit, so that a 450lm light source is roughly equivalent to an old 40 watt bulb, while an 800lm light source is similar to a 60 watt bulb. Comparisons for the most common sizes are in the table below.
Due to the huge variety of possible light levels available from new generation energy-saving and LED bulbs, it’s a good idea to get into the habit of thinking in lumens. It’s also a very good idea to buy spares when fitting multiple light sources in the same space, as wattage is now no longer a guarantee that a bulb will be the same level of brightness. Plus because bulbs lasts so much longer now, if one of your bulbs looks wrong, you won’t be stuck with it for months, but maybe for years!
|Energy-saving bulb||Incandescent Bulb||Average Lumens|
|4-7 Watts||25 Watts||300|
|9-11 Watts||40 Watts||450|
|13-16 Watts||60 Watts||800|
|18-20 Watts||75 Watts||1100|
|22-25 Watts||100 Watts||1500|
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