I'm new to quality flashlights and I could use some insight. I've noticed that some lights might have higher lumen output but lower beam intensity than a comparison flashlight.
As an example, the Nitecore P15 has a max of 430 lumens and a peak beam intensity of 19,321cd, whereas the Nitecore P12 has a greater lumen rating of 950 but a lesser beam intensity of 12,450cd.
1) Is beam intensity largely a factor of reflector size/shape?
2) Would I be correct in saying that throw distance is more a function of beam intensity than lumen output?
3) Is lumen rating solely a function of light emitted from the diode or is is effected by reflector size.
4) Everybody seems to talk about lumen output but not much about cd. Is cd rating much of a concern?
Just trying to sort out a few variables that are new to me.
RJ
Go Here:
http://www.candlepowerforums.com/vb...-Easy-to-Understand-Lumens-Vs-Lux-Explanation
Summary of your Inquiry:
1) Partly
2) Yes
3) Partly
4) It depends on the context
Lumens represent the light sent out into the darkness....as a total quantity of light. You can't see lumens, you can only see lumens that were sent out of the light if they hit something and bounce back to your eyes.
What you SEE essentially, is what we call lux. The brighter the target looks, the higher the lux.
If you have a given lumen output, and concentrate it into a smaller area on a target, that area will look brighter (Have a higher lux value). If you spread those same lumens out over a wider area, the area will look dimmer.
An ordinary 100 watt light bulb might be putting out ~ 1,800 lumens, but, you could not see very far with it, because the lumens are very spread out. If you put a reflector behind that bulb, it takes ~ 1/2 the light that was "going the wrong way", and sends all the light more in one direction....so you would see farther with that same bulb, and so forth.
Lux is the lumens per square meter, so, whatever the beam size is, at a given distance, that's the square meters of target it's illuminating. The more lumens hitting the target, the more lumens per those square meters...and the brighter it will look.
cd, for throwers, is the BACK CALCULATED lux at one meter, as a way of standardizing the comparisons in throw. If you know the lux at one meter, you can calculate the lux at any given distance.
Lumens are of course generated by the LED, but, there are more factors to the flashlight's total output in lumens than just which LED, some examples:
The LED could be driven harder to it put out more lumens, or softer, to produce fewer lumens, perhaps to allow it to run longer on a set of cells, etc.
The LED could be positioned so that some of the lumens are bouncing back into the flashlight through the hole in the reflector. (The depth and orientation/centering, etc, of the LED relative to the reflector bowl, etc)
The flashlight could have a glass or plastic lens that is not 100% transparent to light, so that the lens is absorbing or reflecting some light back, and less than 100% of the LED's output is able to escape, and go light something for you. This difference can be visually noticeable in some cases where a poor lens is used, with losses in double digit percentages being somewhat common.
The LED could have a dome over it, or, have no dome. The de-domed LED presents a smaller point of light to the reflector, which is easier to focus (A reflector works best with a theoretical point source, so, the larger the area that is emitting the light (the LED, etc), the softer the focus will be. A de-domed LED has a smaller effective surface area than if its dome were still on, and, can therefore throw farther, as the light will be closer to a point source in nature. IE: A smaller LED with the same lumen output can generally throw farther than a larger LED with the same lumen output. The LARGER LED's lumen out put would have to be enough to compensate for its larger area, to out throw the smaller LED. Some XML2 (A larger LED) lights CAN out throw XPG2 (A smaller LED) lights because the XML2 CAN be run hard enough to compensate for their larger size for example.
Of course, generally, the larger the LED, the larger the reflector would be to take advantage of it/have the geometry to allow focusing of it:
For an LED, the DEPTH of the reflector bowl is often more important than the diameter, as an LED throws most of its light forward, not back into the bowl, so a deeper bowl is needed to have more of the escaping light hit it, but both play an important role in how well the light is collimated.
For a normal reflector, we see a hot spot, where the most concentrated part of the beam is, a bright circle of light centered in the beam typically. Around that is a donut of somewhat dimmer but still bright light called the corona. Light that missed the reflector (The bowl wasn't as wide or as deep as needed for the lumens made by the LED to hit the reflector bowl and be bounced back in to be focused and collimated)...just randomly spills out, and is called "spill".
So, for most lights, that means SOME of the lumens are in the hot spot (The most important part for throw), and SOME of the lumens are in the corona (Useful for medium range beam thickness so you can see more at a time), and SOME of the lumens will be in the spill (Which some people like as it provides some soft lighting for seeing simultaneously close up, even though your flashlight is mostly searching off in the distance, etc)
The PROPORTIONS of the lumens in these three beam parts, and the SHAPE/AREA of each part, dictate the overall beam characteristics.
For example, if two lights have the same exact throw, one could do it with 1,000 lumens, and one could do it with 10,000 lumens...but one of the beams shows just a man's head at 100', and the other shows the man's head, torso, and the 30 other guys standing next to him and where they tied up their horses.
One light's hot spot might be fatter, with a smaller corona, another might have a teeny hot spot with a large corona, and so forth.
The cd only tells you how far you could see what at, but not how much of the target will be illuminated, just the distance. (Could be the same cd with 1,000 lumens or 10,000 lumens, etc)
The lumens tell you the total output, but not the distribution.
The beam angles can tell you more about the distribution, but, you'd need the beam angles for the hot spot and the corona to get a reasonable overall characterization of the type of beam a flashlight might be sending out.
The ways to evaluate a flashlight's beam are quite varied, and as mentioned, focusing on one metric, such as lumens, or cd, is like buying car solely on its horsepower, or mpg, etc....rather than considering its weight relative to that horsepower or cargo/passenger capacity relative to that mpg, and so forth.
I hope that gives some context for you.
