When measuring the brightness and output of a light bar or driving light, there are two common numbers that are used to help understand a light’s brightness: Lumens and Lux.
While these ways of measuring light are related, they are not interchangeable – and represent different ways of looking at the brightness of a light. It can seem a little confusing – but we’re going to look into the difference…
What do they mean?
While both lumens and lux measure light, they do so in different ways. Let’s start by looking at the definition of each term.
Lumens definition
Lumens – The measurement of light emitted by a bulb. It only looks at the light source.
Imagine you have a lit light bulb, and you place it in a shoebox – the bulb is going to fully illuminate that space with lots of light. Now if you take that same bulb and place it in the middle of a dark warehouse, the same bulb isn’t going to light up very much at all. The lumens are the same, but the impact of the light is altered by environmental factors.
Lux definition
The word “lux” originates from the Latin word for “light”, meaning “illumination, brightness or radiance”.
Lux is a unit of illuminance which measures the intensity of light on a surface. It considers different factors such as distance from the light source and the direction of the light.
Lux measures the amount of light on a surface – so if you shine a torch at a wall from 1 meter away, it will illuminate the surface. Move back 5 meters and it will still be illuminating the wall, but it will be much dimmer. The torch itself hasn’t got any dimmer, but the light is being spread further around the room, meaning less light is hitting the surface of the wall. Now if you shine the light through a tube at the wall, you’ll see that less light is escaping into the room, and the surface is brighter.
So the lumens of the torch are the same, but the Lux has increased – One lux is equivalent to one lumen of brightness per square meter – so over a space of one meter squared, a surface with one lux is as bright as a bulb giving off one lumen at point-blank range.
Why lux is an important measure for driving lights?
Lux is important when looking at driving lights as it shows you how effective the source is at lighting the way. You want a light that is excellent at illuminating the way ahead (the lux) and the brightness at point blank range (the lumens) is not so relevant.
A good way to think about this is the lux is the distance at which you can be away from the light source, and still have enough light to read a newspaper – so 1 lux at 1km means that at 1km away from the source, there will be enough illumination to light up the newspaper.
How are lux and lumens related?
When it comes to driving lights, lux is arguably the best measurement to look at, as it gives you more of a real-world idea of how they will light up the way ahead.
However, typically a higher lumens rating will directly impact the lux – a brighter light generally goes a further distance.
While this isn’t always the case, the way we design our lights gives you optimum lux for the lumens – in other words, we can get excellent range on our lights from less lumens, meaning they are more efficient.
Lux to Lumens Conversion Calculator
The formula
The formula to calculate illuminance (lux) from luminous flux (lumens) and area (in square meters) is:
Conversely, if you know the illuminance (lux) and the area, you can calculate the luminous flux (lumens) using the formula:
Keep in mind that these calculations assume that the light is evenly distributed over the specified area. If the light distribution is not uniform, additional factors may need to be considered.
Conversion Chart
If you’re trying to calculate from lux to lumens this handy conversion chart will help.
If we assume an area of 10 square meters, we can create a table of example Lux to Lumen values using the formula:
| Lux | Lumens |
|---|---|
| 1 | 10 |
| 10 | 100 |
| 50 | 500 |
| 100 | 1000 |
| 500 | 5000 |
| 1000 | 10000 |
What is 1 Lux?
1 lux is equal to 1 lumen per square metre.
What you’ll read in product descriptions is usually measured in lux units at a certain distance. For example, a light will offer “1 lux at 1km”. This means that your beam will illuminate an object 1km away to a brightness of 1 lux, or 1 lumen per square metre.
How Bright is 1 Lux?
To put this into perspective, 1 lux is the accepted amount of light needed for a person with 20:20 vision to be able to read a newspaper. So you’ll be able to read the paper a kilometre down the road; if that’s what you fancy.
Ways of measuring this value can vary, but lux values are generally accepted as a good standard measurement of how your lights will perform on the road. As a rule of thumb, if the lux levels are high but the lumens are low, your beam will be narrow. If the lux is low the beam will be wide, but won’t project far down the road.
Keep in mind that lux readings can be taken ‘on the road’ or in laboratory conditions. Readings taken on the road are more realistic, but also more difficult to get. A lab test will usually take a measurement at 25 metres in ideal conditions and then simply multiply the results to get a number for 500 meters or 1km, which means that in the real world the results may be very different.
What is Usable Light?
Be wary of the term “Usable Light”. It is very vague. Lux is a real objective measurement, usable light is not.
Some companies will claim that 0.5 lux is a usable brightness, but this will depend on how good your eyesight is and what you are hoping to see.
With 0.5 lux of usable light, you’ll see a car 5 meters away without difficulty. However, you probably won’t see a kangaroo 50 metres away. While a usable light value doesn’t explain much in itself, it can be used as an objective reading of how far a light will shine when compared to other lights that display the same scale.
We make it easy by giving you Lux and Lumen measurements
Here at Ultra Vision, we make it easy by giving you both lux and lumen measurements on our lights.
This way, you can see how powerful each model of light is at source AND how this converts into the more helpful measurement of how effective that power is at a distance.
By using these numbers, you can get the perfect light for your particular area – driving a lot in built-up areas? Then maybe the lumen and lux measurement can be lower, as you won’t need to see as far ahead, and can avoid glare off of road signs or dazzling other drivers.
Heading out into the bush with nothing for miles around? Perhaps you want the maximum lumens and lux that we offer to help light the way!
