GIVE A LUX AND KNOW YOUR LUMEN
— March 02, 2018
Difference between Lux and Lumen
Lux and Lumen are both used to describe the performance or beam of lights, but what does each actually mean? In simple terms, Lumen is the volume of light emitted, and lux is the intensity or brightness of the light hitting a surface. Lumen has a nice scientific definition (in the interest of keeping this article simple – please Google the scientific term) but its origins come from the light produced by 1 standard candle. Lux is a little harder to get your head around – Lux is 1 Lumen of light spread evenly on an area of 1m x 1m.
LUMENS: Volume of light emitted from the lamps.
Maybe some examples might help make it clearer. Take a standard 55w or 60w halogen globe that is typically fitted to headlamps. These output around 1,500 Lumens and most of this makes it way out of the headlamp onto the road, and in most cases the High Beam and Low Beam functions produce about the same Lumens (amount). Yet most of us would describe the High Beam as brighter than the Low, and it certainly has a longer beam than the Low Beam. This is because the Low Beam spreads the light over a wider area, while High focuses the light into a narrower beam to give distance. While both have about the same Lumen, the High Beam will have a higher Lux at any given distance. So you can see that while Lumen is the total amount of light, Lux is more about the focus.
LUX: Intensity or brightness of the light at a measured point in the distance. At 1 lux it is possible to read a newspaper.
Historically work lamps have been measured in Lumen and driving lamps measured largely in Lux, and this makes sense if you think about it. A wide flood work lamp’s performance doesn’t require the light to be focused onto a small area, rather it needs a wide even spread of light. So its performance depends largely on the total volume of light: Lumens, whereas a conventional driving light is all about focusing the light down the road as far as possible. This is best measured in Lux at a distance, given 1 lux is generally accepted as enough light to read a paper by. Most lights are measured down to 1 Lux, meaning how far away the light can be from the source while still shining 1 Lux of light on a surface. For example a light might be 1 lux 900 meters meaning if you held a sheet of paper up in front of the light 900m away it would have 1 Lux of light falling on it.
The advent of L.E.D - based driving lights and bars has seen both Lux and Lumen used to describe performance, because these lights typically shine wider than traditional Halogen or HID lamps, but not as wide as a work lamp. This can leave them a bit stuck in the middle with the Lux and Lumen measurements. However, the very best L.E.D lamps have both high Lumen output and long 1 Lux distances, which means you should get the best of both worlds – a wide beam with good distance.
So to really fully understand the performance of a light you need to know both Lumen (power) and the Lux (focus). Of course there is much more to consider such as the beam angle or half power angle, colour rendering and so on, that go to making a great light… But these are topics for another day.