What is a Lumens Rating? The Answer is a bit long, but with a little time come some of the most usefull lighting information you need to know as an officer or a soldier.
A lumen is a unit of standard measurement used to describe how much light is contained in a certain area. The lumen is part of a group of standard measurements known as the photometry group, which measure different aspects of light. This group also includes such units as the candela, which measures luminance, and the lux, which measures illuminance.
Strictly speaking, a lumen is defined as one candela multiplied by one steradian, which can be expressed as: 1(lm) = 1(cd) x 1(sr). A related unit of measurement — although not part of the standard units — is the foot-candle, which is often used in photography and film. To really understand what a lumen is, it is important to understand these units: the candela, the foot-candle, the steradian, and the lux.
Differences between lumina(lumens) and lux. (FAIRLY SIMPLIFIED)
The difference between the units lumen and LUX is that the LUX takes into account the area over which the luminous flux is spread. A flux of 1000 lumina, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumina, spread out over ten square metres, produces a dimmer illuminance of only 100 LUX. Mathematically, 1 lx = 1 lm/m2.
Many people have thought to use this mathmatical calculation in order to calculate the lumina of a projected beam device such as a flashlight/torche. Some have distanced themselves from a surface sufficient to spread a flashlight beam 1 meter and have made luminia calculations based upon the lux reading taked. This however is scientifically impossible as such deviced always have a factor of “wasted” or “cascaded” light, making such calculations erroneous. Such calculations will generaly be inaccurate by as many as several hundred percent. Therefore there is no scientific field calculation which can even remotely convert LUX to luminia (lumens) when discussing flashlight which utilize polished or coated reflectors..
Why is Lumens and acceptable rating for a theatre projector, but not a flashlight?
The reason Lumens is an acceptable rating for theatre projection devices and not for flashlight projection devices is quit simple.
Theatre projection devices utilize optical magnifier lenses to accurately eliminate 99% of “cascaded”, or “wasted” light. This means that the light is being precisely focused onto the surface area intended, and almost no light is lost outsite the area of focus.
Although there are some flashlights which utilize high quality optical magnifier lenses to project a beam, most do not.
99.99% of all flashlight including the most expensive models available today, use highly polished/coated reflectors.
Light projection devices which use these highly polished or coated reflectors (such as almost all flashlights) have cascaded light which is not part of the center beam or “hot-Spot”. This may be by design or because of poor quality. Between as much as 100 and 1000% of the light emissions may therefore be lost in the cascaded light. Thus explaining for the gross performance variation for lights bearing the same or similar lunen ratings.
Typically, companies putting more time and money into the development of their flashlights achieve much higher lux ratings at much lower luminia outputs and therebye increase the efficiency of their lights while also increasing their run-time and battery life. This causes what therefore is known as a “brighter” light with regards to visual performance, to actually have a smaller impact on the natural environment due to the saving of energy through this efficiency… Luminia increase therfore generaly means more power consumption, while lux increase may well be a sign of better manufacturing if battery efficiency is increased.
Luminia has been a chosen rating by many flashlight companies in recent years to the surprise of the scientific community. Whereas lux is a quantifiable performance rating which can determine the actual distance a projected beam can travel, and is therefore an acceptable and accurate performance rating,… luminia, or lumens, have very little to do with the calculatable performance of any such projection devices which use polished reflectors. This explains why no two beam projection devices(or flashlights) which have the same “lumens” rating actually perform the same;…many differing in projection strength as much as 1000%.
Luminia, or lumens is therefore the perfect rating for a flashlight if you want to hide the actual projection performance of a beam. Lux is the optimum characteristic if actual performance of a beam projection device is desirable.
Now let’s look at luminia and the lights in our households and businesses. A single fluorescent fixture with an output of 12000 lumina might light a residential kitchen with an illuminance of 500 lux. To light a factory floor with area dozens of times that of the kitchen would require dozens of such fixtures. Lighting a larger area to the same level of lux requires a greater number of lumina.
In the end it all comes down to ethics.. Use LUX if you want a useful measurable unit which can easily convert to useful information on the battlefield….Use Lumens if you feel the need to hide your lights performance behind a measuremeant which can leave your performance a mystery..