DIY PAR meter, Yeah you heard me

[Chlorophile]

I wonder what you could do with 3 sensors, each with their own cellophane color filter on them!

[Hoppy]

Originally Posted by mistergreen

... You can go ahead and build the sensors. This filter isn't a big deal since Nobody has odd color bulbs. It's out of curiosity. The range of human perception seems to work fine.

I agree. Since you calibrate the meter it will be plenty accurate for all of the commonly used planted tank bulbs. If this was for lab use, where very accurate measurements of nearly equal PARs was needed, then it could be a problem. When I was playing with the PAR meter two days ago I noticed just how sensitive it is to very small mistakes. I don't think I could do a calibration that I would swear was accurate to better than 10%. To do that I would want some kind of fixture that held the PAR sensor very precisely where it was supposed to be.

[O2surplus]

OK, I'll go ahead and build them with the original materials. I've got a 5 day weekend coming up, so I should have some time to get a few built.

[theblondskeleton]

If you wanted more precision in the filter, check out Rosco gel filters (or GAM for that matter). If you check out the website, you can order a swatchbook that has small samples of each filter with a card showing the spectral energy distribution curve for each filter. Takes the guesswork out. These should also be available at any stage/film/DJ lighting outlet. The swatch is about 2"x4" so you could probably equip all 20 units with one of these from one swatch book. Here's a link:

http://www.rosco.com/filters/roscolux.cfm#colors

[O2surplus]

Originally Posted by theblondskeleton

If you wanted more precision in the filter, check out Rosco gel filters (or GAM for that matter). If you check out the website, you can order a swatchbook that has small samples of each filter with a card showing the spectral energy distribution curve for each filter. Takes the guesswork out. These should also be available at any stage/film/DJ lighting outlet. The swatch is about 2"x4" so you could probably equip all 20 units with one of these from one swatch book. Here's a link:

http://www.rosco.com/filters/roscolux.cfm#colors

Hey thanks for that link. They've got a ton of color choices there and good documentation. Now the question becomes what color filter would be the best choice? If PAR is normally found in the red and blue regions of visible light, wouldn't we want to use a green/yellow filter to reject NON Par producing wavelengths? Or is it the other way around and we'd use red/blue?

[mistergreen]

You'd want the magenta or lavender filters like the cellophane I used. That spectral graph is what plants look for.

But since we don't use yellow and green light bulbs over our tanks, the regular sensor without the filter will work fine, not super accurate.

[O2surplus]

We don't use yellow and green bulbs per se, but those two colors are included in sources of "white light". So don't they contribute enough energy to raise the output of the photo diode and throw off the actual PAR value?

Originally Posted by mistergreen

You'd want the magenta or lavender filters like the cellophane I used. That spectral graph is what plants look for.

But since we don't use yellow and green light bulbs over our tanks, the regular sensor without the filter will work fine, not super accurate.

[theblondskeleton]

You would use a lavender colored filter, which filters out green and amber to a higher degree than the red and blue. A low saturation filter would likely be best, as it maintains a higher amount of red/blue, but the compromise is more green/yellow gets through. Typical balancing act

[mistergreen]

Originally Posted by O2surplus

We don't use yellow and green bulbs per se, but those two colors are included in sources of "white light". So don't they contribute enough energy to raise the output of the photo diode and throw off the actual PAR value?

Yes, they are included in white light but only a portion and not the total. That's why I wanted to play with the cellophane. Could the sensor be more accurate with the lavender filter? Sure.
Does it need it for the hobby? Not sure. Depends on cost and such.

[mistergreen]

Oh, if you want to play with it, go for it. You have the apogee sensor to do some comparisons.

[theblondskeleton]

Rosco's R52 "light lavender" looks like it would be an excellent choice.

http://www.rosco.com/filters/SED.cfm?titleName=R52:%20Light%20Lavender&imageNam e=../images/filters/roscolux/52.jpg

It retails around $7.00 for a single 18"x24" sheet. That would go a very long way, haha... I have some lying around somewhere as I use this color a lot. I could send a small sample if you want to play around and see if it makes any difference.

[mistergreen]

Here's the photosynthesis spectrum for comparison

[Hoppy]

This looks like the one that would work best. Green and yellow add to the PAR, and they should do so. Removing all of those two colors leaves you with a number that isn't PAR. It looks like this filter removes about the right amount to make this comparable to the Quantum meter.

[Jeffww]

What modifications would I need to make to measure PAR under relatively blue reef lighting?

[mistergreen]

Originally Posted by Jeffww

What modifications would I need to make to measure PAR under relatively blue reef lighting?

none.. it might be wonky if you have yellow or green light.