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The emergence of LEDs and energy saving light bulbs has made choosing replacement bulbs a lot trickier than it used to be. As a cutting-edge technology, LEDs are constantly and rapidly becoming more efficient. One manufacturer may release a 5 Watt LED which replaces a 40 Watt bulb and then a few months later, a different manufacturer might introduce a 5 Watt LED which replaces a 60 Watt bulb! This has made the Watt fairly redundant as a measurement of how bright a light bulb will be...

What is a lumen?

Lumens (lm) are a measure of the amount of light which is visible to the human eye from a lamp or light source. The higher the lumen rating, the brighter the lamp will appear. It is a more accurate measure than watts for denoting the brightness of a lightbulb. A typical household lightbulb will emit between 200–500 lumens, while a high-powered floodlight could emit in excess of 20,000 lumens.

Watts don’t necessarily measure the brightness of a bulb, only the amount of electricity it uses. With so many new bulbs giving out the same amount of light but at an increasingly lower wattage, we need to compare bulbs by how much light they actually give out. From now on you will start seeing a ‘lumen’ value listed on the side of light bulb boxes.

Lumen Chart
The above graphic is taken from our Crompton 5W LED GU10's spec sheet.

Lower Wattage + Higher Lumens = Better Value

You’ll still see the wattage shown on the box, but you shouldn’t use this to gauge how bright the bulb will be. It’s just there to compare the amount of electricity used with the brightness of the bulb, which will be shown in lumens - often shortened to ‘lm’. This is why bulbs with a lower wattage/energy consumption and higher lumen output represent much better value.

While this will help consumers in the long run, it’s going to be a bit of a nightmare to get used to; we all knew where we stood with a 60 Watt bulb! So, here’s a table showing the brightness (in lumens) of the more popular traditional filament bulbs and their relative LED equivalents. Learn these and you’ll always know where you stand - a 400lm bulb is a 400lm bulb, irrespective of whether it uses a filament or LED. The only difference will be in their respective wattages, where the former's will most certainly be higher...

Watts to Lumens

Watts v Lumens comparison


These figures are approximate and used only to illustrate the correlation between various wattages and lumen values.

Remember - the higher the Lumen, the brighter the bulb!