The Truth about Lumen Why Lux and not lumen? First of all we have to define Lux and Lumen. Lumen is the value that states the total optical power of a bulb or LED, in other words the light that is emitted in ALL directions. That means, if a LED has 1000 lumen then this LED is beaming the 1000 lumen in ALL directions, therefore 360° degrees. The term Lumen describes general lighting e.g. kitchen light, living room light, stadium lighting or street lighting and therefore the only right way to measure the light intensity. Lux would be nonsense here. So in all these examples it goes that the light source emits 360 degrees. In dive lights the light emits approximately 5-15 degrees FORWARD and not 360 degrees EVERYWHERE. Now, this point is very important for us as divers. We do not want to have light emitting in all directions, but focused into one direction, in fact, pointed precisely forwards as much as possible. This seems logical, because what does it help us if the beam is shining everywhere including backwards? We want the light focused in whatever direction we point it and not all around us. Now, that is how Lux comes into the game.
The Lux value predicates how much optical power still arrives at the spotlighted object. Here is an example: A workplace regulation states that a light source must provide three fee/one meter of distance in a workplace (e.g. desk) with at least 1000 lux, so that this work place is illuminated well. Now it is becoming clear that it is not useful to install a light bulb with 1000 lumen into the desk light, because we still do not know if the 1000 lumen light bulb does bring the 1000 Lux on the desk. Remember, 1000 lumen is a measurement of light in all directions, but 1000 Lux is the measure of the light that arrives at the specified location. Let’s look at this in regards to diving lights now.
The detail that a diving light has 1000 lumen says absolutely nothing about it, rather, we want to know the Lux optical power that arrives at the object the light is focused on. Now critics will say (or competitors) that Lux indications cannot be compared at all because the irradiation angle is not the same. In principle this is correct because only the same irradiation angles can be compared with each other. However, this statement is wrong in reference to diving lights because all diving lights have proven themselves a very narrow irradiation of about approx. 6-15 degrees as the general standard. This means that all common diving lights have a narrow irradiation forwards and therefore they are comparable to each other. So why do the manufacturers publish the lumen performance, but not the Lux performance? For exactly this reason: because they don’t like it to be comparable! We take the following example to this: We have two diving lights: Dive light “A” has 500 lumen and dive light “B” has 1000 lumen. “A” creates with 500 lumen 15,000 lux and “B” creates 1000 lumen with only 13,000 lux. Every diver would immediately know now that “A” is brighter than “B” and would buy “A” of course (if the optical power would be the only decision criterion). But this is not what the manufacturers want. So they prefer to indicate nebulous values which say nothing about the actual brightness.
TillyTec is one of only a few manufacturers which give the Lux optical power. TillyTec has already asked the competitors to publish the Lux values of their lights many times, but obviously the fear dominates that they will lose even more customers because of that. Perhaps they do know how bright their lights really are and therefore they do not want to publish the Lux values at all. The only way to check lumen is in a laboratory and this will cost $5,000 and up per light! To check Lux it will cost around $30 for a luxmeter at amazon.com or any home improvement store. You can do this by YOURSELF. The higher the lux number, the brighter the light! The TillyTec LED 3000 dive light with 60,000 Lux is the smallest and brightest dive light with the longest burning time worldwide at the time of this writing!
Following another explanation why Lux is more important for dive lights than lumen: The term lumen describes the general illumination value of light. Back to the examples with the kitchen, living, stadium or street light, where lumen is very important and the only thing what counts. Lux wouldn’t make any sense here with what we already know. What does the customer want to know now exactly? The human nature is curious like a cat and wants to know what the human eyes can see. Well, that is simple. The human eye can see approx. between 0.2 lux and 100.000 lux. Therefore to an example: 0.2 is a moon night and 100.000 lux a nice, cloudy free sunny day. What difference can the eye see if it sees two light sources together? This depends very much on the Lux value. If as an example you have 100,000 Lux, then you cannot recognize 70,000 Lux directly besides that as darker, which means you cannot compare both Lux together at the same time. Imagine you have a light which has 500 Lux and another one which has 1000 Lux. You can see the difference very easily and clearly. If you, however, have a light with 15,000 Lux and one with 11,000 Lux, you can barely see the difference, if the eye is practiced well. As a rule of thumb of dive lights you can say that 30%-50% difference can still be seen by the eye. 100% is a superb plain brightness augmentation.
To this another example with our light heads: The LED 500 light head has 15,000 Lux The LED 1500 light head has 30,000 Lux You can see the difference very clear!!! ( 100 % more light/brightness ) The LED 750 has 25,000 Lux The LED 1500 has 30,000 Lux Here it is very hard to see the light difference with your eyes only!! (only 20 % more light/brightness) The LED 1500 has 30,000 Lux The LED 4500 has 50,000 Lux The LED 3000 has 60,000 Lux Here it is very clear to see the light difference just with your eyes!! (50 % – 100% more light/brightness) Here is another very good example for your understanding: We take our LED 4500 and LED 4500 Video. Both light heads have 2700 Lumen and are absolutely identical. While LED 4500 has 50,000 Lux, the LED 4500 Video has only 3000 Lux. It is easy to compare both lights and tell which one it brighter although both have the same lumen numbers. That is no magical trick. LED 2000 has 10 degrees irradiation and LED 4500 Video 110 degrees irradiation.
So, we want to keep in mind: Lux is FORWARD and Lumen is EVERYWHERE, because on this planet there is no single diver who wants the light everywhere but forwards. Hopefully it is more understandable and clear now why Lux is more important for dive lights.