LUX vs. LUMENS
- Thread starter Turbo6
- Start date
Help Support Candle Power Flashlight Forum
Jace
Newly Enlightened
I'm still new and learning as well, and this would be my WAG, but for the same reasons that motorcycles are rated by cc's, and cars/trucks are rated by litres. If I were to put my 7.3 litre truck engine in my CBR-600, it would become a CBR-7300 turbodiesel!
And I would probly upgrade the headlight with HID. /ubbthreads/images/graemlins/smile.gif
And I would probly upgrade the headlight with HID. /ubbthreads/images/graemlins/smile.gif
Think of Lux as measurement of an area of light (square meter of light, to be precise) from a meter away. And think of Lumens as a measure of total output of light that's being produced by a single source.
Both are different measurements, and both really do not correlate with each other. Comparing one to the other can be quite misleading. A high Lux light may not have much lumens, because the beam it casts may be very narrow and intense, but the bulb may not produce much light. But a floodlight may not produce a high lux reading, yet its total light output in lumens will exceed the aformentioned high lux light...
In short, they're different units of measurements that are intended to show different types of applications for a light source...
Both are different measurements, and both really do not correlate with each other. Comparing one to the other can be quite misleading. A high Lux light may not have much lumens, because the beam it casts may be very narrow and intense, but the bulb may not produce much light. But a floodlight may not produce a high lux reading, yet its total light output in lumens will exceed the aformentioned high lux light...
In short, they're different units of measurements that are intended to show different types of applications for a light source...
Jonathan
Enlightened
[ QUOTE ]
FalconFX said:
Think of Lux as measurement of an area of light (square foot of light, to be precise) from a meter away. And think of Lumens as a measure of total output of light that's being produced by a single source.
Both are different measurements, and both really do not correlate with each other.
[/ QUOTE ]
1 correction and 1 expansion.
The _Lux_ is a measure of the light falling on a surface, measured in terms light _quantity_ per _unit area_. The lumen is a measure of total light, or light _quantity_.
As FalconFX said they are _not_ correlated in the sense that given any two light sources one might have a high lux measurement and a low lumen measurement, or vice versa.
However the two measurements _are_ related by a well defined mathematical connection.
In particular, a lux measurement when multiplied by an area gives a lumen value. This means that if you have a square meter of surface, evenly illuminated, and 1 lux is falling on that surface, then the total light falling on that square meter will be 1 lumen.
Similarly, if you have 1 lux falling on 1 cm^2, then the total light on that 1 cm^2 is 1/10000 lumen.
Finally, if you make measurements of lux values from a surface which surrounds a light source, and associate each lux value with a patch of area of that surface that is evenly illuminated, and then multiply that lux value by that area, and sum it all up, you will get a total lumen value for the source. (Whew!) This is _integrating photometry_, and is often done with an integrating sphere, where the math is done by the hardware (the big sphere) rather than by lots of measurements and calculations.
The small correction: for the Lux, the unit of are is the _square meter_. 1 Lux is 1 Lumen per meter^2.
-Jon
FalconFX said:
Think of Lux as measurement of an area of light (square foot of light, to be precise) from a meter away. And think of Lumens as a measure of total output of light that's being produced by a single source.
Both are different measurements, and both really do not correlate with each other.
[/ QUOTE ]
1 correction and 1 expansion.
The _Lux_ is a measure of the light falling on a surface, measured in terms light _quantity_ per _unit area_. The lumen is a measure of total light, or light _quantity_.
As FalconFX said they are _not_ correlated in the sense that given any two light sources one might have a high lux measurement and a low lumen measurement, or vice versa.
However the two measurements _are_ related by a well defined mathematical connection.
In particular, a lux measurement when multiplied by an area gives a lumen value. This means that if you have a square meter of surface, evenly illuminated, and 1 lux is falling on that surface, then the total light falling on that square meter will be 1 lumen.
Similarly, if you have 1 lux falling on 1 cm^2, then the total light on that 1 cm^2 is 1/10000 lumen.
Finally, if you make measurements of lux values from a surface which surrounds a light source, and associate each lux value with a patch of area of that surface that is evenly illuminated, and then multiply that lux value by that area, and sum it all up, you will get a total lumen value for the source. (Whew!) This is _integrating photometry_, and is often done with an integrating sphere, where the math is done by the hardware (the big sphere) rather than by lots of measurements and calculations.
The small correction: for the Lux, the unit of are is the _square meter_. 1 Lux is 1 Lumen per meter^2.
-Jon
Joe Talmadge
Flashlight Enthusiast
[ QUOTE ]
However the two measurements _are_ related by a well defined mathematical connection.
In particular, a lux measurement when multiplied by an area gives a lumen value. This means that if you have a square meter of surface, evenly illuminated, and 1 lux is falling on that surface, then the total light falling on that square meter will be 1 lumen.
Similarly, if you have 1 lux falling on 1 cm^2, then the total light on that 1 cm^2 is 1/10000 lumen.
[/ QUOTE ]
But, since companies who publish lux measurements never ever ever publish data on the size of the area being measured, knowing that lux can theoretically be translated to lumens is of no practical use, would you agree?
For practical purposes, you should read lux measurements as a measurement of the brightest part of the beam, but you're getting no information about how big that bright part is, or how much total light is being put out. There are lights that have high lux measurements but pencil thin beams that are not that useful. Lumens measure the total light put out, but you have information about how bright or big the beam might be. A 60W light bulb would have an enormous lumen count, but obviously that light is evenly distributed and no one part of the "beam" is all that bright.
Joe
However the two measurements _are_ related by a well defined mathematical connection.
In particular, a lux measurement when multiplied by an area gives a lumen value. This means that if you have a square meter of surface, evenly illuminated, and 1 lux is falling on that surface, then the total light falling on that square meter will be 1 lumen.
Similarly, if you have 1 lux falling on 1 cm^2, then the total light on that 1 cm^2 is 1/10000 lumen.
[/ QUOTE ]
But, since companies who publish lux measurements never ever ever publish data on the size of the area being measured, knowing that lux can theoretically be translated to lumens is of no practical use, would you agree?
For practical purposes, you should read lux measurements as a measurement of the brightest part of the beam, but you're getting no information about how big that bright part is, or how much total light is being put out. There are lights that have high lux measurements but pencil thin beams that are not that useful. Lumens measure the total light put out, but you have information about how bright or big the beam might be. A 60W light bulb would have an enormous lumen count, but obviously that light is evenly distributed and no one part of the "beam" is all that bright.
Joe
Here is everything you didn't want to know about light measurement:
http://www.intl-light.com/handbook/ch07.html
thanks to Quickbeam for linking to this site. I think it's best to compare apples to apples, and foot-apples to foot-apples (or convert to meter-apples). FYI, 1 foot-candle is 10.76 lux (so sayeth my HP28s anyway).
~ned
http://www.intl-light.com/handbook/ch07.html
thanks to Quickbeam for linking to this site. I think it's best to compare apples to apples, and foot-apples to foot-apples (or convert to meter-apples). FYI, 1 foot-candle is 10.76 lux (so sayeth my HP28s anyway).
~ned
Quickbeam
Flashlight Enthusiast
Actually, if your foot-candle is measured at one foot, it's the same as Lux measured at one meter. It's a one to one ratio when measured at the specified distances. /ubbthreads/images/graemlins/thumbsup.gif
Jonathan
Enlightened
[ QUOTE ]
Quickbeam said:
Actually, if your foot-candle is measured at one foot, it's the same as Lux measured at one meter. It's a one to one ratio when measured at the specified distances. /ubbthreads/images/graemlins/thumbsup.gif
[/ QUOTE ]
Not quite.
Both the foot candle and the lux are measures of the illumination of a surface, and the conversion factor is 10.76 to 1 as described above.
But if you wish to compare the light _sources_, you want to use either Lumen (for total light output) or Candlepower (for intensity of the beam.)
You can use a device which measures foot candles or a device which measures lux if you wish to measure the candlepower of a light source, and this is where the two different measurements can come together to the same units.
A light source of 1 candlepower will produce an illumination of 1 foot candle at a distance of 1 foot.
A light source of l candela will produce an illumination of 1 lux at 1 meter.
Candlepower and candela are historically related, and essentially the same.
So if you have a device which measures _lux_ and place it 1 meter from a source, then you will also be measuring the candela of that source. Similarly, if you have a device which measures foot candles, and place it 1 foot from a source, then you will be measuring the candlepower of that source. Since candela and candlepower are essentially the same measurement, the results (measuring lux at 1 meter or foot candles at 1 foot) will be essentially the same measurement of the light _source_.
-Jon
Quickbeam said:
Actually, if your foot-candle is measured at one foot, it's the same as Lux measured at one meter. It's a one to one ratio when measured at the specified distances. /ubbthreads/images/graemlins/thumbsup.gif
[/ QUOTE ]
Not quite.
Both the foot candle and the lux are measures of the illumination of a surface, and the conversion factor is 10.76 to 1 as described above.
But if you wish to compare the light _sources_, you want to use either Lumen (for total light output) or Candlepower (for intensity of the beam.)
You can use a device which measures foot candles or a device which measures lux if you wish to measure the candlepower of a light source, and this is where the two different measurements can come together to the same units.
A light source of 1 candlepower will produce an illumination of 1 foot candle at a distance of 1 foot.
A light source of l candela will produce an illumination of 1 lux at 1 meter.
Candlepower and candela are historically related, and essentially the same.
So if you have a device which measures _lux_ and place it 1 meter from a source, then you will also be measuring the candela of that source. Similarly, if you have a device which measures foot candles, and place it 1 foot from a source, then you will be measuring the candlepower of that source. Since candela and candlepower are essentially the same measurement, the results (measuring lux at 1 meter or foot candles at 1 foot) will be essentially the same measurement of the light _source_.
-Jon
Quickbeam
Flashlight Enthusiast
Boy... Try to keep it simple around here and see what you get! /ubbthreads/images/graemlins/twak.gif /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/smile.gif
