Cheapest PAR Meter DIY - Page 5 - The Planted Tank Forum
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post #61 of 65 (permalink) Old 02-25-2016, 10:25 PM
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Hoppy I'm thinking about ordering one of these as is. I'm gonna take apart the sensor and silicone like you showed to waterproof. Then using the lux meter reading lux, I then divide whatever number it says by 78? Correct? This cheap diy stuff can get confusing
Yes, that's correct. You use the meter as it is designed to be used, and it measures in lux. Divide the lux value by 78, or for some lights the number to use is as low as 70, and you get about the right PAR reading.

Don't forget how hard it is to get the sensor completely waterproof. I was successful once, but other times it would eventually seep a little water in, and stop working until I dried it out, not easy to do. This was so frustrating to me that I finally decided that it would be best for me to just use it by propping my light across a couple of chairs, and measuring the lux at the same distance from the light as the substrate was, then divide by 78 (I finally switched to 70 as the divisor, but I forget why )
Would propping it on some chairs still give you an accurate reading? I would think the dead air would give you a higher reading then it would be going through water.
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post #62 of 65 (permalink) Old 02-25-2016, 10:47 PM
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Would propping it on some chairs still give you an accurate reading? I would think the dead air would give you a higher reading then it would be going through water.
somewhat the opposite.. Water refracts the light and light hitting objects/glass has a tendency to bounce it back in..

not much of a difference but some..esp. deeper in the tank.

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post #63 of 65 (permalink) Old 02-26-2016, 10:39 PM
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Would propping it on some chairs still give you an accurate reading? I would think the dead air would give you a higher reading then it would be going through water.
somewhat the opposite.. Water refracts the light and light hitting objects/glass has a tendency to bounce it back in..

not much of a difference but some..esp. deeper in the tank.
So even doing it in dead air no water would give you about the same reading as it would in water?
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post #64 of 65 (permalink) Old 02-26-2016, 10:54 PM Thread Starter
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So even doing it in dead air no water would give you about the same reading as it would in water?
Yes. When I have checked this I almost always got about the same PAR reading in the water as out in the air. Considering all of the other inaccuracies in measuring PAR the lack of water has a minor effect.

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post #65 of 65 (permalink) Old 02-27-2016, 02:19 PM
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So even doing it in dead air no water would give you about the same reading as it would in water?
Yes. When I have checked this I almost always got about the same PAR reading in the water as out in the air. Considering all of the other inaccuracies in measuring PAR the lack of water has a minor effect.
Well hell im just gonna get one of those lux meters since they aren't even $20 and do it that way
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