Easy to Understand Lumens Vs Lux Explanation

[reppans]

Re: Integrating sphereLux to lumens, final conversion confusion

I happen to followed this post from the general section...

So you get an integrating sphere as described elsewhere on these forums. You make sure you surce cannot directkly strike the meter sensor. The whole idea is to make the light source as diffuse as possible. You measure the lux. Then what? One thread said you divide by 36. Why? Doesn't the ratio of the entire sphere's area to the area seen by the sensor (or the area of the sphere) come into play here? That was what I could not find, either here or looking elsewhere.

Thanks for any help

Not to take anything away from what TEEJ said on a proper sphere and calibration, but most of us use cheap homemade contraptions that are "close enough" and if nothing else, perfectly fine for at least relative measurements between similar lights.

So, for DIY light boxes, your lux>lumen multiplier depends on the efficiency of your lightbox and is simply the "plug" multiplier between your lux reading and lumen output of your trusted calibration light. Mine happens to be a nice even 10x multiplier using a $5 PVC plumbing elbow rig .

I calibrate to ti-force's lumen scale, the only reviewer on CPF to claim laboratory ANSI accuracy, and since his scale matches most of my lights/modes anyway . I also always use lower modes to calibrate since max output tends to have more sample variation, and is very battery sensitive.

 

[OldNick]

Re: Integrating sphereLux to lumens, final conversion confusion

5 characters

 

[TEEJ]

Re: Integrating sphereLux to lumens, final conversion confusion

I happen to followed this post from the general section...



Not to take anything away from what TEEJ said on a proper sphere and calibration, but most of us use cheap homemade contraptions that are "close enough" and if nothing else, perfectly fine for at least relative measurements between similar lights.

So, for DIY light boxes, your lux>lumen multiplier depends on the efficiency of your lightbox and is simply the "plug" multiplier between your lux reading and lumen output of your trusted calibration light. Mine happens to be a nice even 10x multiplier using a $5 PVC plumbing elbow rig .

I calibrate to ti-force's lumen scale, the only reviewer on CPF to claim laboratory ANSI accuracy, and since his scale matches most of my lights/modes anyway . I also always use lower modes to calibrate since max output tends to have more sample variation, and is very battery sensitive.

It doesn't take away from what I said.


Its just a question of degree. For example, the DIYS work best when comparing similar beam patterns, etc, but tend to fall short when the throw or flood is different, or the tints are different, etc.

A real IS of course uses a radiometer type meter, not a home style lux meter...etc.


On the other hand, if you feel your home made version is "close enough", you could submit it to ANSI for certification, and then sell a ton of them to fools who shelled out thousands of dollars for your competitor's ANSI certified IS.

:twothumbs


Seriously though, we ALL try to make out own versions, and, they CAN be pretty good...but, ALL will have the limitations imposed by the throw/flood issue, because none will be able to completely integrate the beam and homogenize the output.

Given the cost of a "real one", its typically the DIYS, or nothing.

 

[domdbomb]

Thanks for explaining! My friend kept telling me that it's not about the lumens when you're concerned about the brightness, and now I understand what he was talking about. Great way to put it.

 

[Mark Yan]

i think the lumen like pressure and the lux like intensity of pressure...:kiss:

 

[scs]

i think the lumen like pressure and the lux like intensity of pressure...:kiss:

I've always thought of lumen as the total force and lux as the pressure at a location (stress) at a given distance. Lumen is total output; lux is intensity at a given distance.

 

[TEEJ]

The lumens are the total supply, and, the lux is how its distributed...so, the higher the lux, the less distributed/more concentrated, those lumens are.

Again, as lux is the lumens per square meter, if you make the same lumens cover a larger surface area, the lux will be proportionally lower.

If you make the same lumens cover a smaller area, the lux will be proportionally higher.

If you keep the area covered the same size, but double the lumens, you are also doubling the lux...and so forth.


So, yes lux is definitely a way to express the intensity of the illumination produced on a target.

Lumens are just what you have to work with as a total supply....for your eventual lumens per square meter concentration.

 

[reppans]

I like the pressure/force analogy, I think I'll use "weight" going forward.

Imagine lying on the floor and a beautiful 115 lbs (lumen) woman lays directly on top of you > mule (no pun intended). Next she stands on a large book on your chest > flooder..... Coke can > thrower.... Long masonry nail > laser (and you die ).

 

[TEEJ]

I like the pressure/force analogy, I think I'll use "weight" going forward.

Imagine lying on the floor and a beautiful 115 lbs (lumen) woman lays directly on top of you > mule (no pun intended). Next she stands on a large book on your chest > flooder..... Coke can > thrower.... Long masonry nail > laser (and you die ).

I didn't know how kinky you were.

Now I have laser mule woman in my head....

 

[reppans]

Now I have laser mule woman in my head....

 

[ACOLJNSD]

It's nice to know that someone's differentiating between brightness, lumens and lux or footcandles. From an optical standpoint, there are equations that governs all of these parameters. And not only the parameters, but how they relate and what they mean. Brightness or Radiance is flux/(A*O) where Flux is lumens, A is the Area and O is the solid angle. Irradiance is flux/Area and Intensity is flux/Solid Angle. To convert Intensity to Irradiance, simply divide the Intensity by the distance squared. So if a flashlight has a centerbeam candlepower of 5000cd, the irradiance is 5000Lux at one meter or 5000 ft-candles at one foot. At 464ft, the irradiance is 0.023ft-candles or 0.25LUX. This corresponds to the ANSI FL1 standard for distance.

 

[TEEJ]

It's nice to know that someone's differentiating between brightness, lumens and lux or footcandles. From an optical standpoint, there are equations that governs all of these parameters. And not only the parameters, but how they relate and what they mean. Brightness or Radiance is flux/(A*O) where Flux is lumens, A is the Area and O is the solid angle. Irradiance is flux/Area and Intensity is flux/Solid Angle. To convert Intensity to Irradiance, simply divide the Intensity by the distance squared. So if a flashlight has a centerbeam candlepower of 5000cd, the irradiance is 5000Lux at one meter or 5000 ft-candles at one foot. At 464ft, the irradiance is 0.023ft-candles or 0.25LUX. This corresponds to the ANSI FL1 standard for distance.

LOL

This thread was for those who needed a lay version of how to understand the concept. If they got the math, it would not be needed.

 

[renovipaz]

Good information, Thanks!

 

[kostas147]

After this thread I understand the difference between Lumens and Lux!!! :thumbsup:

 

[eric1565]

I have always wondered about that. thanks

 

[kill bill]

Thank you for the info, makes it a little clearer!

 

[Rivine]

thanks for your clear explanation about lux vs lumen. it was very much helpful for me.

 

[TEEJ]

I'm glad it helped!

 

[Rolz]

Thanks for the easy explanation. To be honest I've never really looked for an explanation of the difference and assumed one could be derived from the other, but clealry not.

 

[forbes617]

very helpful