In the good old days before LEDs, Energy Saving and Compact Fluorescent lightbulbs, you knew what you were getting if you bought a 40, 60 or 100 watt lightbulb. You could easily imagine the amount of light a 100 watt lightbulb would put out - too bright probably for a small bedside table lamp but fine for a hanging light in the centre of a room.
Similarly, a 40 watt lamp would be suitable for a decorative wall light and a 60 watt bulb would be good for general purpose lighting.
All that went out of the window when energy saving lightbulbs made an entrance, now you needed to know that 11 watts were roughly equivalent to 60 watts and 23 watts roughly equivalent to 100 watts.
Then along came LED bulbs and fittings and the ball game changed again - everything LED was measured in Lumens (or maybe Candelas!) and terms such as Lm and Lux (one lux is equal to one lumen per square metre) made an appearance. So, when specifying LEDs, how can we understand what we are getting?
At the time of writing the pace of development in LED light output and efficiency is astonishing. Every day my inbox groans with competing claims from manufacturers in China and the Far East as well as Lighting manufacturers around the world who are using LEDs manufactured abroad in their own light fittings.
Most lamp manufacturers do not publish lumen output ratings for halogen MR16 lamps. Instead, they publish beam angle and other information, which provide more accurate information about the performance characteristics of the lamp. The Lighting Research Center (LRC) tested several 50-watt MR16 samples of the same type (EXN) to determine their lumen output, which ranged between 560 lumens to 710 lumens, and averaged 625 lumens.
So, if we are looking for a downlight with approximate light output to a 50 watt halogen, we need to be looking for around 625 lumens.
However, whilst a very approximate guide it can therefore be said that to get the same sort of light output as a 50 Watt Halogen you need a 625 Lumen LED or to get the same light output as a 35 Watt Halogen you need 425 lumens.
Nevertheless, you should bear in mind that when comparing the lumen ratings for Halogens vs LEDs, the halogen lumen rating will be higher because of the Infra Red output which the human eye cannot see anyway! LEDs do not emit IR so their lumen rating will lower EVEN THOUGH their actual received brightness as you see it may be brighter!
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