Do lumens reflect badly on the industry?

Why is it that the light output of LED reflector lamps such as GU10s and MR16s often disappoints users who have switched from halogen lamps?

There has been plenty of debate about the performance claims of LEDs, and discussion about their light output generally revolves around Lumens. But in the case of directional lighting we think this is where things are going wrong.

For example, manufacturers often claim that a 5W LED reflector is equivalent to a 50W halogen reflector, but is that accurate? One obviously turns to the manufacturer’s product data but here it starts to get complicated – and unclear.

lux-chartThe light output from directional light sources has in the past been measured in Lux at various distances from the source, and with good reason. Directional lighting has a job to do: deliver light to specific places. So it makes sense to measure the actual amount of light that arrives there. Light that doesn’t arrive should be, well, filtered out from the figures. A Lumen count, on the other hand, will include light that from the user’s perspective has wandered off in the wrong direction. Lux is clearly the way to go, then.

We decided to see for ourselves, so compared the Lux values of a 50W halogen reflector against an LED ‘equivalent’ and concluded that the LED was only just over half the output of the halogen. Why should this be? Is there a technical answer or are LEDs simply trying to punch above their weight?

With so many different light sources now available there is obviously a need to standardise units of measurement, and Lumens make perfect sense for non-directional lamps. For directional lamps, though, they do not give a true picture of the useful light. Indeed, “Useful Lumens” is a term that has recently been introduced into EU vocabulary. It is a measurement of light emitted in a standardised 90 degree cone. Unsurprisingly, the Useful Lumens rating is normally lower than the total Lumen output. It is a step in the right direction.

But Lux gets our vote.


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