Easy to Understand Lumens Vs Lux Explanation

TEEJ

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To understand lumens and lux, start with the concept that you can't SEE lumens. Lumens are a measure of the total light sent OUT by the flashlight.

What you SEE is the light that hits something, and bounces back to your eyes. THAT light that you SEE is referred to as LUX. The brighter the OBJECT looks to you, the higher the lux.

When a person says a light is "bright", they might mean it gives you high lux, or, high lumen values...or both....but, might not know why.




If you imagine that water is lumens, and its depth is brightness, so that the deeper the water, the brighter it looks to you...and you look down into a shot glass of water, say an inch deep...and see that brightness in that little glass...

...and then dump that shot glass of water into a kiddie pool, so it spreads out into a wide film of water....it will look "dimmer" but be the same number of lumens.



Humans suck at judging brightness in of itself...but you can see more with more lumens, but, most of the added vision is to the sides in a broad pool of light...and less is added to a central hotspot.

The hotspot generates glare, and the eye tells the brain that more glare = brighter....so people TYPICALLY will say a 100 L focused beam is "brighter" than a 1,000 L floody beam, as the floody one didn't glare and tell the brain how bright it was.



If you looked into the kiddie pool, and saw the dim light, you'd say, "that flashlight is dim".

If you looked into that shot glass, you'd say "that flashlight is bright!".


They both put out exactly the same amount of water/lumens though.


Lux is the lumens per square meter on the target....so, the more lumens you have, the easier to spread them out and still have enough lux to see targets.


If your beam spot is 10 square meters in size, you'd need ten times more lumens to have it look as bright as if it were focused down to only 1 square meter in size.

IE: For the same "brightness", you'd need 1,000 lumens to get your 10 square meters to look as bright as the 1 square meter would look with only 100 lumens.


This is why a guy with a 100 lumen light with a tight beam might say "its impossible to read with it because there's too much glare", but a guy with a 500 lumen floody beam can read the same page with no glare.


:D
 
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TEEJ

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sigh (There were some posts deleted for the sake of brevity/clarity)

:D

For the record...10 square meters (The way I was using it) is not 10 meters by 10 meters, its representing Length X Width = 10.

As we are actually discussing a flashlight beam, its typically ROUND anyway....so a round area that covers 10 square meters is (In my world) might have a diameter of ~ 3.5682 meters.




∏ times the radius squared = 10

:D

For a SIMPLE explanation though, I try to avoid terms like ∏, etc.


For the inverse square law, I like to think of it as the light getting 4 times dimmer when you double the distance, or 4x brighter when you cut the distance in half, etc...



Can a mod trim off the superfluous posts after the first one to clean this up a bit?

- Thanks!

(Cataract, bro, you are cracking me up)
 
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TEEJ

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I've used that idea too, but I think people get lost in it when there's no visual.

Pressure = brightness seems harder to get than depth = brightness...as they can visualize depth and not pressure.

I wanted to explain lumens vs lux more than how to get throw vs flood per se...with an easy way to visualize what each is about.
 
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Cataract

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The pool analogy explains lumens VS lux best
The shower head analogy explains throw VS flood best. I believe that if you do a small revision with that in mind it would make an excellent way to explain throw and flood to newbs..


2 completely basic things that do have some common ground. Perhaps an organized cumulation of plainly explained concepts like these could be made into a full introduction course. For now, it might be best to keep these analogies separate and them point to them through a master thread.

p.s.: I take full responsibility for the deleted posts. I've been bad... Sorry TEEJ!
 
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Fresh Light

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I'd like an alcohol analogy.

Lux being the alcohol percentage
Lumens being the actual amount of alcohol in the container
Tint is the particular brand, flavor, or vintage
CRI is the score on ratebeer or winespectator
 

ShineOnYouCrazyDiamond

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TEEJ - thanks for this explanation. I had a grasp on the concepts but this made it very easy to understand.

Poppy- BTW, the explanation of yours on the garden hose is also a perfect way to help explain to people the difference between Volts and Amps. Where volts is the pressure pushing the water out of the hose and Amps is the amount of water being pushed.
 

TEEJ

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TEEJ - thanks for this explanation. I had a grasp on the concepts but this made it very easy to understand.

Poppy- BTW, the explanation of yours on the garden hose is also a perfect way to help explain to people the difference between Volts and Amps. Where volts is the pressure pushing the water out of the hose and Amps is the amount of water being pushed.

You are welcome.

:D
 

Cataract

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TEEJ [...]

Poppy- BTW, the explanation of yours on the garden hose is also a perfect way to help explain to people the difference between Volts and Amps. Where volts is the pressure pushing the water out of the hose and Amps is the amount of water being pushed.

Basic electronics are very easy to explain by using plumbing comparisons. That's exactly how my first electronics teachers taught us Volts, Amps and capacitors. In my particle/optical physics classes, we also had to experiment with water to understand the basic principles. Your statement is more than true. If only I had enough time I would try to write up similar threads on all the basic principles about flashlights and water analogies. I hope this thread helps start a new trend of teaching all the basics on flashlights.
 

TEEJ

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Basic electronics are very easy to explain by using plumbing comparisons. That's exactly how my first electronics teachers taught us Volts, Amps and capacitors. In my particle/optical physics classes, we also had to experiment with water to understand the basic principles. Your statement is more than true. If only I had enough time I would try to write up similar threads on all the basic principles about flashlights and water analogies. I hope this thread helps start a new trend of teaching all the basics on flashlights.

I could see a new wave of analogies flowing from this source.
 

njhart

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Very useful! Actually this is my first trip to CPF (I've long been aware, but hesitant to jump full in to more gear collecting) and this was one of the things I wanted to know.
 

TEEJ

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Very useful! Actually this is my first trip to CPF (I've long been aware, but hesitant to jump full in to more gear collecting) and this was one of the things I wanted to know.

Excellent!

We try to help people learn what they came for.

:D
 
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