Hello and thanks for reading. I was curious if there is a compelling reason to use an underwater meter to determine when it's time to change bulbs. If I take initial readings over a nuetral color at x height would that do the job?
Par Meter
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Crabs McJones
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I meter mostly at top. I have a center brace in one tank and lids on the other so I can find the same spot.
I actually encourage folks to meter this way to help understand the fields of light in the tank.
Dana Riddle
2500 Club Member
I can read your question a couple of ways. If you're wondering if there is a preference of a submersible meter v. non-submersible, then my 2 cents worth says go for the one capable of underwater measurements. There are a number of factors that a non-submersible probe can't see - for example, focusing of light by surface wave action (shimmer, glitter, caustic network) and selective attenuation of UV/violet/blue wavelengths by organics that 'yellow' the water and results in low light readings. The second interpretation is about the neutral color, but more importantly, the height. Take all precautions necessary to standardize the position of the sensor. As you probably know, light fields can change drastically in short distances (inches) and single measurements can be useless unless sensor positioning is exactly the same. Did this answer your questions?
OP
OP
Thanks. You did answer my question. Any recommendations on which PAR meters to purchase? I'm mainly looking to compare various fixtures I own and to determine when to change my bulbs.
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Dana Riddle
2500 Club Member
PAR meters have come a long way in the last few years, and the less expensive meters now compete with the 'lab grade' instruments such as LiCor. Apogee Instruments offers sensors that are cosine-corrected and have good spectral response, and meters are capable of data logging. They also offer USB sensors. Seneye's device isn't cosine-corrected and I have a report from a source that I trust that it generate useful measurements.
If you are member of a Marine Aquarium club they generally have one to use for participating members. in my club I go to the members house and help them with checking their lighting as it takes a couple of people to do it right. One to hold the meter probe and one to write down the readings.
Dana Riddle
2500 Club Member
Ed makes a good point - clubs often purchase a meter for members' use. Might save you some bucks.
The SQ-520 will have a better spectral response than the BioTek Marine but they're always tethered to a computer. The MQ-210 also has limitations to its spectral response when compared to the SQ-520. With that said, there isn't a giant difference when comparing readings from these devices - do we really care if PPFD is 500 or 540? Probably not. You probably know this - BioTek Marine is a private label for sensors made by Apogee.
Apex unit is meant to be installed in a tank. Not my favorite way to use a Par sensor. As it can get a bio film on the senor throwing off the reading.
Dana Riddle
2500 Club Member
I'm not familiar with Apogee's software for the SQ-520. Hopefully, you can toggle between 'air' and 'underwater' measurements. Glad to hear you joined the PPFD Club. Every serious aquarist should have (or have access to) a quality quantum meter.
Sleepydoc
Valuable Member
One note of caution - I'm not sure that a PAR meter is the best method to determine when you need to change bulbs. PAR meters don't show you spectrum, rather they give an aggregate number of the amount of light within a certain spectrum range. As bulbs age, the spectrum shifts and you can have the same PAR reading with a different spectrum.
No. It’s the best.
You can also use a lux meter.
Both take a tiny amount of practice.
Same “Caution” could be said if any test. Cal alk no3 Po4.
Overblown caution imo.
Dana Riddle
2500 Club Member
Yes, there is a better method, but it is going to cost you - a spectrometer, or a radiometer,at least a $1,000 US, and probably much more. Method of measurements in order of 'common sense' preference: quantum meter (starting at $199 U,S.); lux meter (cheap, but beware of cosine correction and ability to be submerged); spectrometer, fiber optic (such as Ocean Optics) and spectroradiometer (requires conversion, complications.) Go with the quantum (PAR) sensor - it is the best compromise.
Apogee MQ-510 was my choice after a lot of research. It is already corrected for use underwater, is fast and consistent (I was going to say accurate, but I have no basis for comparison).
I use it myself at least weekly. I also use it to help other people who are curios what kind of par X light is at what distance. I has helped me to figure out that Hydroponics T5 fixtures are fine over a frag tank and fuge and still put out massive amounts of light at shallow depths.
I also used it to tune in my Halides over my new tank... I was 550+ over the entire bottom and I do have a few that acropora I like to be around 350 with (Dragon Varieties). They would have been fine under 550+, but their color would not have been as rich. The other stuff that I keep is fine up to 750, or sometimes, more, but I did need a few places where it was lower. I angled the reflectors where I had some lower light spots, but also an area in the sand where I was at about 625 where I can put my clams.
The main thing that I use it for it help folks who get coral from me find a place where they can put it in their tanks, or at least know where it came from. Example, trade a LE Blue Matrix the other day... put the sensor right next to the coral at 475 PAR. Let the guy borrow the meter... he was 275 to 310 all over his tank... he is thinking about different lights, but at least he knows that if it looks different, one of the explanations might be 200 PAR difference.
