Equipment & Techniques > Beginner's Questions
LED-How to tell the real ligthing output of led lights?How to compare lighting p
haring:
I am looking at several led light options. Obviously, one of the considerations is how much light the led panel emits.
Some companies list their products specifying out put via "lux"
http://www.adorama.com/fpvl500c.html
Others list Watt, W.
http://ikancorp.com/productdetail.php?id=998
Others use lumens...
My questions: How to measure/compare the lighting output of led lights? Is there a way to convert these numbers? All I want to know how much light these lights output so I can compare them.
GrahamBy:
Lumen is the unit of measure the actual light output, whereas Lux is the unit of the intensity of that light reaching what you want to photograph:
ie if light A has 4 times as many Lumen as light B, but you place it twice as far away, the inverse square law predicts there will be the same illumination.
I've made the gross assumption of both lights having the same spread of light: a concentrated beam will yield more illumination (Lux) than a wide flood for the same total output (Lumens).
So if the output is specified in Lux, it should also specify at what distance the light is placed. If it's specified in Lumen, you're a bit stuck without knowing the beam pattern.
You can then convert Lux to Ev (for a given ISO) using the chart here:
http://www.sekonic.com/support/evluxfootcandleconversionchart.aspx
Bart_van_der_Wolf:
--- Quote from: haring on January 13, 2016, 09:50:47 am ---My questions: How to measure/compare the lighting output of led lights? Is there a way to convert these numbers? All I want to know how much light these lights output so I can compare them.
--- End quote ---
Hi,
You can try this calculator.
I haven't tested whether it's absolutely correct, but that is basically the input needed for a conversion. Lumen is a total flux of light (in all directions, or concentrated by a reflector), Lux is the amount of light a given surface area receives or emits (usually expressed per square metre, if you want to avoid angles and distance).
One Lux is one Lumen per square meter, but for conversion you would need to know how the flux in Lumen is spread and the distance at which it is measured.
Watts only tell something about the power consumption, nothing about how efficient that power is transformed into visible light (and e.g. heat).
Cheers,
Bart
P.S. Here are some more calculators.
digitaldog:
--- Quote from: haring on January 13, 2016, 09:50:47 am ---My questions: How to measure/compare the lighting output of led lights? Is there a way to convert these numbers? All I want to know how much light these lights output so I can compare them.
--- End quote ---
You could measure the this using something like an i1 Pro Spectrophotometer from X-rite and a number of software options (BableColor). You could get this info and a lot more about the illuminant.
http://www.babelcolor.com
BobShaw:
Measure it with a light meter at say 2m. As Metallica would say, nothing else matters.
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