Right. Good point.
Point is, you can have 800 unfocused, very floody lumens that are almost useless unless for a very specific application.
Or focused 120 lumens that are more useful in almost all applications.
Case in point, I have a Malkoff M60L, the original, 5+ year old device, "Low". It's just such a nice balance of thrown and high lux that I consistently found it more useful than even more recent, higher-powered units such as Malkoff M91. The latter had considerably more lumens (was it 800 or something to that effect) but it felt like holding a household lightbulb in your hand. All flood, no throw. Useless beyond room distance. Ended up selling M91. Still use M60L.
M60L has higher lux than the higher powered M61.
A couple examples pulled from the web. One light is 2350 lumens / 22K lux and the other is 3550 lumens / 23K lux. For the moment, disregarding the human eye & inverse square law about perceiving brightness. Both of the lights are listed as "great throwers." Is 1200 lumen difference for a 1K gain in lux a result of LED efficiency? Beam angle?
...For the most part, they are flooders. Due to the large number of lumens they output, they also gain some throw...
...Assuming the numbers are OTF (out-the-front), ANSI FL 1 lumen ratings, then the difference between the two flashlights you cited is most likely due to beam angle or a difference in spill/hot-spot brightness.
(BTW, I don't mean to nitpick, but just in case you do not already know, the proper term is "candela," rather than "lux." Without getting bogged down in too much detail, we can say that candela is the maximum lux that can be found, i.e., measured, at any position that is exactly 1 meter from the emitter. Usually, this means dead center in the hot spot, but not always.)
If I'm following you correctly, the gain in throw is due to power. Even though it's a flood reflector enough light is being forced out the front and it has to go somewhere.
Regarding the second part of the quote. Not sure if the numbers are OTF. They came from 2 different lights from the same manufacturer. I used them just as an example to confirm my guess about beam angle.
As to the third part of the quote, I didn't take it as nitpicking Always glad to learn something. My inference is that this is similar to resistance & ohms. Lux is the topic & candela the numerical value.
Thanks! I'm glad you liked it.
It's one of the more technical explanations in this thread, but I think it gives a fairly accurate description of the difference between lux and candela, especially as the latter term applies to flashlights.
There is an unstated assumption that TEEJ has made throughout this thread. All of his targets are facing directly toward the flashlight, so that his flashlight beams strike them head on, i.e., perpendicularly.
If, for instance, the target is the side of a building, the building must be facing the flashlight. If it is not, then you must use the dot product, as described above, in order to determine the lux on target.
This makes sense.
Suppose, for instance, that the flashlight beam is a circle 10 meters in diameter when it strikes the building. If the building is facing the flashlight, then a section 10 meters wide will be lit by the flashlight. If, however, the building is angled to the flashlight, a much longer section may be lit up. For purposes of discussion, let's say that a 20-meter section gets lit.
The lumens have not changed, but the area being lit up has changed. Because the area is larger, the number of lumens per unit area will be less, i.e., the lux will be less.
From this example, you can see that the angle at which a light beam strikes a surface, i.e., a target, plays a role in determining lux!
The definition of a flashlight's beam intensity, as measured in candela, is designed to eliminate this dependence.
When you model a flashlight as a point source, and place a sphere of radius 1 meter around it, all the stuff about tangent planes, normal vectors, and dot products goes away. That's because every light beam is perpendicular to the surface of the sphere, no matter where it strikes it.
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance (lux) is inversely proportional to area when the luminous flux (lumens) is held constant.
One lux is equal to one lumen per square metre:
1 lx = 1 lm/m2 = 1 cd·sr/m2
The illuminance provided by a light source, on a surface perpendicular to the direction to the source, is a measure of the strength of that source as perceived from that location.
The illumination provided on a surface by a point source equals the number of lux just described times the cosine of the angle between a ray coming from the source and a normal to the surface. The illumination provided by a light source that covers a large solid angle is proportional to the cosine of the angle between the surface normal and a sort of barycentre of the light source, so long as all of the source is above the plane of the surface. The number of lux falling on the surface equals this cosine times a number (in lux) that characterizes the source from the point of view in question.