Whether it is a torchlight or a headlight in your vehicle, you may often hear about terms like lumen or lux. They both sound similar and often mistaken with each other. But lumen and light are totally different units, even though they both are related to the amount of light.
Both lumen and lux came from Latin words, and their meanings are the same too – Light. And since they both represent the amount of light in different situations, the confusion between them is understandable.
Our goal here is to give you some quick explanations and make you aware of where to use which one. We also described the calculation process of lumen and lux.
What Is Lux
Lux is a unit that indicates how much light is touching a surface or going through it (If it is transparent/semi-transparent). One lux is the equivalent of one lumen projected on a square meter of surface area. Lux does not have any plural form, for example, 100 lux.
The number of lux changes based on the angle, distance, and size of the targeted surface. If those factors increase, the lux decreases. For example, 1000 lumen on one square meter means 1000 lux, but the same lumen on 10 square meters means 100 lux.
Lux unit follows the inverse square law, which is basically something that we summarized above. This law says that the intensity of a light that falls on a surface is inversely proportional to the distance of the surface squared. So, doubling the distance between the light source and the surface makes the lux four times lesser.
What Is Lumens
Lumen is the total measurement of light output from a source in all directions. Its short form is lm, and it slowly replaced the usage of watts to feature the brightness of a light source. By official definition, a lumen represents a candela of light towards any one-meter distance from the source of the light.
If we summarize that, it basically indicates the brightness of a light. Keep in mind that the key point here is that lumen means the overall light output towards one direction from the source.
You may wonder why we use lumen now to indicate headlight brightness instead of the watt, which people used to utilize before. In the past, most lights were incandescent bulbs and halogen headlights. Manufacturers from everywhere used the same materials to create them. So, the higher watts, the brighter those bulbs were.
But now, we use many types of bulbs, like HID, LED, CFL, etc. They have different efficiency, and some can produce more light output than others using the same wattage. So, the new unit people started to use is lumen that focuses on the overall light output (brightness), not the energy usage amount.
Where to Use LUX
Lux is an excellent unit to figure out how much light intensity you will be getting throughout your room if you buy a new bulb. Since lux represents the amount of light falling on the surfaces, it will let you find out the amount of light each floor and wall of your room will get. Once you get some necessary information, you can calculate it on your own.
As you can understand, the lux isn’t really a necessary unit for headlights. But since headlights with more downward visibility are better, they should have a higher lux to be better. Keeping the lumen constant, if a headlight’s lux is reduced, its light is more widened out.
Where to Use Lumens?
The answer to that question lies in the very definition of lumen itself. As the measurement of light output, lumen must be used in cases where one needs to determine the brightness of a light source.
As we mentioned earlier, the lumen has replaced the traditional wattage on product descriptions. No matter whichever light type you are using, the lumen can give you a perfect picture of its brightness.
When buying a new pair of headlights, you will find lumen on its description more likely than lux. Lux is not always necessary when it comes to learning the brightness of torchlight or headlight.
Which Is Better? Lux or Lumens
Honestly speaking, that is a wrong question. Lux and lumen are units related to light. Both are better in particular contexts.
If you are into vehicles and buying headlights, you should check the lumen output of the bulbs. Lux doesn’t matter that much here.
On the other case, if you are buying a bulb for a room, you may calculate the lux to have a clearer picture of the light intensity on every corner. All you must do is use the right term at the right time. It will be easier for you once you learn how to measure the units. We explained that in the next section.
How to Calculate Lux and Lumens
First, let’s talk about the measuring process of lumens. The luminous flux Φv in lumen (lm) is equivalent to the power (P) in wattage (w) times the efficiency (ƞ) in lumen per watts (lm/w).
It goes like this-
Φv(lm) = P(W) × η(lm/W)
It means, Lumens = wattage × lumens per watts.
Or, lm = w × lm/w.
Using it, you should be able to calculate the lumens of any bulb.
The calculation of lux is pretty easy in comparison. Lux basically means the amount of light projected on a square surface. You can use the following equation for it-
Lux = lumens/the surface area
Or, lux = lm/ m2
While both lumen and lux are light related units, there are many difference between them. Hopefully, you can recognize them properly now. When you are buying headlights or torches, make sure to check their lumen ratings.
While this stat may not be totally accurate, it is still close. Using the lumens, you can also calculate the lux of the light. Just measure the area of the surface that the light reaches and divide the lumens with it.