Could you use a camera as a PAR meter? - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 02-05-2011, 12:33 AM Thread Starter
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Could you use a camera as a PAR meter?

If somebody with a PAR meter took some readings of different light levels in a tank and then went back to those same locations and put a white plate in the tank then using a camera with the ISO and F-Stop set to a fixed value see what the camera calculates for a shutter speed when amid at the white plate. Then you could build a table of PAR vs. shutter speed at a fixed ISO/F-stop.

Could this work?

Roger
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post #2 of 10 (permalink) Old 02-05-2011, 12:36 AM
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i know you can do this for foot candles, but only as an estimate. im not sure about a par meeter....let me know if you find anything


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post #3 of 10 (permalink) Old 02-05-2011, 12:43 AM
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that would have a lot to do with the minute variables of ambient light that would drastically change your readings ... after you built an acceptable range of ppm to shutter speed # you could work it out I'm sure ( i do some photography myself)

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post #4 of 10 (permalink) Old 02-05-2011, 01:25 AM
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I'm sure it'd work...but I don't know how much you'd be able to generalize those results to other people's tanks / cameras if you were looking to make a chart that other people could put to use. That being said, as long as the camera you are using has spot metering as an available option, I'd think it would be a reasonable approach.

You could always test it out by making the chart, then using the camera to meter another tank, convert it with the chart, and confirm with the PAR meter. If you end up with accurate results in a few different settings...you'd be on to something IMO
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post #5 of 10 (permalink) Old 02-05-2011, 02:17 AM
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The problem is that when you measure PAR you are only measuring the amount of light at the wavelengths that are useful to plants for photosynthesis (mostly from 400-500 nm and from 650-700 nm), but a camera CCD is going to pick up light across the whole visual spectrum (and actually up into infrared). So if you make a reading with one lighting setup, and then the next lighting setup calculates a faster shutter speed, that means there's more light across the all wavelengths the CCD picks up, but does not necessarily mean it's brighter at the PAR wavelengths.

It's the same problem as when you compare two different fluorescent tubes that might have the same lumens rating (i.e. visible light), but depending on their spectrum one could be putting out a lot more PAR than the other.

Larry
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post #6 of 10 (permalink) Old 02-05-2011, 02:18 AM Thread Starter
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I'd love to but I don't have access to a PAR meter, I hoping that someone with one would give it a try
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post #7 of 10 (permalink) Old 02-05-2011, 02:21 AM Thread Starter
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Quote:
Originally Posted by larryl View Post
The problem is that when you measure PAR you are only measuring the amount of light at the wavelengths that are useful to plants for photosynthesis (mostly from 400-500 nm and from 650-700 nm), but a camera CCD is going to pick up light across the whole visual spectrum (and actually up into infrared). So if you make a reading with one lighting setup, and then the next lighting setup calculates a faster shutter speed, that means there's more light across the all wavelengths the CCD picks up, but does not necessarily mean it's brighter at the PAR wavelengths.

It's the same problem as when you compare two different fluorescent tubes that might have the same lumens rating (i.e. visible light), but depending on their spectrum one could be putting out a lot more PAR than the other.

Larry
That makes sense Larry, oh well it was worth ask anyway.

Thanks,
Roger
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post #8 of 10 (permalink) Old 02-05-2011, 05:20 PM
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Digital cameras do have seperate Red, Green and Blue pixels and you can measure the intensity of each of those with software. Photoshop for instance can display a histogram for each colour. With a bit ot math someone with more time on their hands than me could convert the individual R, G & B readings into a better approximation of PAR than the total exposure reading alone.

Alternatively you could use the apporpriate filters on the lens to measure the wavelenghts you are interesed in individually.

Landau

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post #9 of 10 (permalink) Old 02-05-2011, 08:18 PM
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I have asked the same question, but instead of a camera I have a lux meter.
Actually it is feasible with a lux meter, but you must know the LUX->PAR conversion ratio for each light source.
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post #10 of 10 (permalink) Old 02-05-2011, 08:25 PM
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For most of what we do, the difference between using lux or PAR as a light measurement isn't significant - assuming we are testing cool white/pure white/natural white, etc. sources. That also means you can use the rated lumens output of LEDs or T5 bulbs to get fairly close to the PAR you want, with some manipulations. For my design calculations on PAR for multiple LEDs I am using PAR meter data that I can only get to one significant figure - 1, 2, 3, etc. micromols of PAR. That is likely to be no more accurate than using lux and converting it to PAR. The PAR meter we use is only giving us 2 significant figures up to 100 micromols, so even that isn't super accurate. (A meter reading of 2 micromols means the real value is between 1.5 and 2.5. A reading of 10 means the real value is between 9.5 and 10.5)

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