How do I find an equipment to meassure the light output and throw of my lights? Should be cheap /ubbthreads/images/graemlins/smile.gif and and good /ubbthreads/images/graemlins/wink.gif and available for buying from Europe? As far as i know bu now, you meassure light in Lumens, Lux and Candlepower. Am I right, saying that Lumens is the total output, and the two last ones is the concentration of the light, just in two different scales?
How to measurre the light output?
- Thread starter PrebKlok
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SilverFox
Flashaholic
Hello PrebKlok,
It sounds like you have the basic concepts down...
To measure lumens you need a $10000-20000 integrating sphere and some specialized training. I am not sure where you get those but a Google search should reveal some sources.
Doug (Quickbeam) reports overall output (which is kind of like lumens) with a device he made from a milk carton. Other people set their lights on a table and bounce the beam off the ceiling taking a reading at table level. This is great to check the differences between lights, but the numbers you get will not transfer to other people due to differences in ceiling color and texture.
Lux (and foot candles) are measured with a light meter. These run in the $50-100 range. Bernhard (Kiselling) is in Germany and has one and you may want to send him a message to find out where he got it. A search of this forum should reveal information on several types of meters. I believe a photographic light meter can also be used, but I am not sure of the conversion from EV to LUX.
Please note that lux are usually reported at 1 meter and foot candles at 1 foot. If you take measurements at other distances, please include the distance in you comments so we can figure out what you are talking about. It is usually best to report you meter reading and the distance. If you say your light reading is 100 lux, I will assume that you have taken the measurement at 1 meter. If you say your light puts out 100 lux at 1 meter, there is no possibility of confusion.
Good luck...
Tom
It sounds like you have the basic concepts down...
To measure lumens you need a $10000-20000 integrating sphere and some specialized training. I am not sure where you get those but a Google search should reveal some sources.
Doug (Quickbeam) reports overall output (which is kind of like lumens) with a device he made from a milk carton. Other people set their lights on a table and bounce the beam off the ceiling taking a reading at table level. This is great to check the differences between lights, but the numbers you get will not transfer to other people due to differences in ceiling color and texture.
Lux (and foot candles) are measured with a light meter. These run in the $50-100 range. Bernhard (Kiselling) is in Germany and has one and you may want to send him a message to find out where he got it. A search of this forum should reveal information on several types of meters. I believe a photographic light meter can also be used, but I am not sure of the conversion from EV to LUX.
Please note that lux are usually reported at 1 meter and foot candles at 1 foot. If you take measurements at other distances, please include the distance in you comments so we can figure out what you are talking about. It is usually best to report you meter reading and the distance. If you say your light reading is 100 lux, I will assume that you have taken the measurement at 1 meter. If you say your light puts out 100 lux at 1 meter, there is no possibility of confusion.
Good luck...
Tom
Roy
Farewell our Curmudgeon Administrator
Nicely said! /ubbthreads/images/graemlins/happy14.gif
wasBlinded
Flashlight Enthusiast
A photographic incident light meter can be used for lux measurement at 1 meter.
Here is the formula:
2.5*(2**EV) where EV is for ASA 100
i.e. 2.5 times (2 raised to the power of the EV reading)
Naturally, a digital exposure meter will give the most precise results.
Here is the formula:
2.5*(2**EV) where EV is for ASA 100
i.e. 2.5 times (2 raised to the power of the EV reading)
Naturally, a digital exposure meter will give the most precise results.
Why don't people use a light meter, as silverFox mentions? I hear so often that an integrating sphere should be used. But for a small shop or hobbyist, I cannot see why there would be a functional difference in the result -- just more labor in taking the measurements.
It would work like this: take intensity measurements at regular angular intervals in a half circle, in the plane of the light. Go from behind the light around the side of the bezel to the front. Then numerically "integrate" these values over strips that make up an imaginary sphere, multiplying each intensity by the appropriate area and summing the total. Convert units, and poof, you have output.
The catch is that you have to do this where there is not a reflected light problem, i.e., don't do it in a white room.
I can see why you would pay $10k for equipment if you are Surefire, but the above approximation should be perfectly adequate for informal purposes. You shold be able to get lumens output that way.
Scott
It would work like this: take intensity measurements at regular angular intervals in a half circle, in the plane of the light. Go from behind the light around the side of the bezel to the front. Then numerically "integrate" these values over strips that make up an imaginary sphere, multiplying each intensity by the appropriate area and summing the total. Convert units, and poof, you have output.
The catch is that you have to do this where there is not a reflected light problem, i.e., don't do it in a white room.
I can see why you would pay $10k for equipment if you are Surefire, but the above approximation should be perfectly adequate for informal purposes. You shold be able to get lumens output that way.
Scott
Mike Painter
Flashlight Enthusiast
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- Sep 16, 2002
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If you are talking about a bare bulb with nothing that focuses the light that might work but most lights are not designed this way. In most cases an attempt is made to place most of the light in a particular area and the drop off tends to be very rapid. In most cases aveeraging such measurements would be of less value than doing what is done now. Take a reading in the hottest spot and publishing that.
If the object of the measurement is to get lumens, not lux, you have to measure the entire field. This is true whether you have a bare bulb or a tightly focused beam. Unless the laws of physics changed when I wasn't looking, it will work.
Scott
Scott
