In the good old days before LED’s, 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 Lx and Lux (One lux is equal to one lumen per square metre) made an appearance. So, when specifying LED’s, how can we understand what we are getting?
At the time of writing (February 2011) the pace of development in LED’s 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 LED’s manufactured abroad in their own light fittings.
Downlights – Halogens vs LED’s
Most lamp manufacturers do not publish lumen output ratings for halogen MR16 lamps. Instead, they publish beam angle and light output in candelas, 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.
However, halogen light output will always read higher than a LED because of the level of Infra Red output, but this is misleading because the human eye cannot see IR. LED’s do not put out any IR. So, whilst a very approximate guide, it can be said that to get the same sort of light output as a 50 Watt Halogen you will need around 550-600 Lumen LED and for a 35 Watt Halogen you need 400-425 lumens.
Probably the human eye is the best thing to judge the light output of LED’s after all!