A practical, affordable PAR meter?

[mcarroll]

Sunlight Calculator | Eartheasy.com

Anyone who follows me knows I'm not a huge fan of measuring lights in PAR because the meters are so expensive and the info they give is (in most cases) no more useful than readings you can get with a cheap or free lux meter.

This little unit comes through in a couple of notable ways.

First, at $20, it's acceptably cheap.

Last, instead of pooping out a real-time number (a lux meter will do the equivalent of this for free), this unit takes an accumulated PAR reading over the course of a whole day and converts that to useful information - telling you if the monitored location can be considered in "full sunlight", or another shadier designation. Perfect! I may have to try one (haven't yet) - it would be interesting to know how my LED dimming cycle really adds up in terms of a whole day's illumination.

Let me know if you try one!

-Matt

 

[FX CharityCorals Verified Sponsor]

I would assume its not waterproof but I'm guessing it would work fairly well still sealed in a clear plastic bag? Cool idea

 

[redfishbluefish]

Especially for LED's, how can you compensate for the approximate 10% error of warm whites and blues?


It would also be nice to know what the average PAR numbers would be for the various light levels.....Full Sun, Partial Sun, Partial Shade and Full Shade. I would imagine Full Sun is an average or 400 or so PAR.

 

[mcarroll]

I would assume its not waterproof but I'm guessing it would work fairly well still sealed in a clear plastic bag? Cool idea

You could try a high-quality freezer bag if you don't mind risking your $20 and want to experiment. But if you ask me there's not a lot to gain from measuring below the water surface anyway. If you're just trying to "spot read" a specific coral or area, why bother with the waterproofing, etc? Just use the shadow that the unit casts from the surface to target the coral or area intended.

Especially for LED's, how can you compensate for the approximate 10% error of warm whites and blues?

If you know the error is about 10% then you have your compensation...but there's really no point in this either. 10% apparently isn't enough to be worth quibbling over for our needs.

It would also be nice to know what the average PAR numbers would be for the various light levels.....Full Sun, Partial Sun, Partial Shade and Full Shade. I would imagine Full Sun is an average or 400 or so PAR.

One more reason I'm no fan of measuring in PAR....there seem to be very few useful standards, or few that are well-known.

It's really a linear variation of measuring lux unless you get very high end about it. (Even measuring lux changes quite a bit when you get high end about it.) If you have a lux meter and can borrow a PAR meter, you can calculate the lux-to-PAR conversion factor for your lights and meter. (Most of the variation is with the lights not the meter, so every light combo will have a unique conversion factor.) With that, your lux meter is now a PAR meter. Voila.

Lux is a well-established unit of measure. The Wikipedia entry will even do you well, informing you what several standard lighting levels are. No conversion factors are needed to get the info we need to know.

After some digging on what full daylight is in PAR...it still depends on the units you're using:

"2000 µmol m^–2 s^–1" or "400 W m^–2" can be considered full daylight.​

-Matt

 

[Shtiff1]

Is there a conversion table for lux to par?

 

[Coraloliseffect]

Is there a conversion table for lux to par?

If my understanding is correct. ( please jump in if not)
Could be done knowing the lux spectrum at source and filters going through. It water and particulate in it. But it is kind of a fruit stand conversion from apples to oranges.

 

[mcarroll]

Is there a conversion table for lux to par?

The short answer? No.

The long answer...

If you have a lux meter and can borrow a PAR meter, you can calculate the lux-to-PAR conversion factor for your lights and meter.

I suppose this could be useful if you were trying to compare numbers with someone who'd gathered data in PAR instead of lux. That's a pretty esoteric case though...dunno how far I'd go to get that PAR meter.

If you have a commercial light it's possible someone else out there with the same light who's taken PAR readings. Take the same reading over your tank with your lux meter and combined with that PAR reading you have your conversion factor as well.

-Matt

 

[Shtiff1]

The short answer? No.

The long answer...

If you have a lux meter and can borrow a PAR meter, you can calculate the lux-to-PAR conversion factor for your lights and meter.

I suppose this could be useful if you were trying to compare numbers with someone who'd gathered data in PAR instead of lux. That's a pretty esoteric case though...dunno how far I'd go to get that PAR meter.

If you have a commercial light it's possible someone else out there with the same light who's taken PAR readings. Take the same reading over your tank with your lux meter and combined with that PAR reading you have your conversion factor as well.

-Matt

Thank you

 

[feh]

I have heard of people getting the sensor for a PAR meter and connecting it to a volt meter and finding PAR this way instead of buying the whole unit. There is a little work involved same as using a Lux meter, but at least it really is measuring PAR.

 

[mcarroll]

I have heard of people getting the sensor for a PAR meter and connecting it to a volt meter and finding PAR this way instead of buying the whole unit. There is a little work involved same as using a Lux meter, but at least it really is measuring PAR.

In practice, measuring in PAR doesn't seem to help much vs measuring in lux.

FWIW, most (maybe all) probe-based meters are simply calibrated volt meters.

Like making the conversion factor for a lux meter I think you would still need a calibrated PAR meter at least one time to compare with. I think the probe would have to be darned cheap to make it a worthwhile effort. Otherwise just download a lux meter app to your smartphone or buy a cheapie handheld lux meter from EbAyMazon for less than $20....or the PAR meter I linked in this thread.

-Matt

 

[mcarroll]

BTW, the PAR meter in the first post is made by the same company that makes the soil test kits you'd find for sale in most garden centers/nurseries....so if you search around there should be plenty of retailers that carry or can get this PAR meter. (In addition to the one I linked.)

-Matt

 

[mcarroll]

Here's the mfgr:
Luster Leaf Gardening Products

...which I linked from here:
Luster Leaf Gardening Products - Outdoor Meters & Thermometers

...and a quick excerpt from their FAQ:

Water-resistant... not waterproof. Rain or sprinklers will not affect the unit's operation. However, do not submerge unit in water.

And FYI it looks like you can get it delivered to your local Sears store via Sears.com....lots of nurseries and garden centers carry this line, so call - they may have this as well. It's not hard to find online (sears, kmart, walmart, amazon, ARBICO organics, etc) if you can't find it locally.

Will be ordering from ARBICO this morning.

-Matt

 

[cope413]

$199 pH, NH3, temp, PAR, Kelvin, Lux meter...

I just got mine from Reef Radiance. Pretty awesome little device

Aquarium monitor system - Fish Tank water sensor - seneye

 

[mcarroll]

Very interesting device, and blend of features, but if you're interested in measuring PAR....you're in the price-ballpark if getting a field-grade PAR meter (with no consumables). You're also in the price-ballpark of some popular aquarium controllers. You're out of the price-ballpark of the Sun Calc.

It's also noteworthy that after spending $199 (or more) you still don't get information about your overall daily light levels like you might with the ~$20 unit in the opening post. You still might want the Sun Calc!

At least in theory (mine's in the mail!!), the Sun Calc unit is accounting for all the dimming cycles, dark/storm periods, cloud cover, etc that I'd want to include in a typical day, and then telling you if that's enough light to still count as (e.g.) "full sunlight".

-Matt

 

[cope413]

Actually, you do get overall levels. In fact, it updates and stores light readings every 10 seconds. You can specify "top", " middle" and "bottom", place the device in the desired spot, and get a complete chart/graph of PAR, Lux, and Kelvin.

I plan on playing with it for the next few weeks to see exactly where my tanks at

 

[mcarroll]

I'm not sure charting the day's levels (data) is the same thing as telling you whether the day's events add up to a "full sun" day vs a "part sun" day (information). But with a little added research and some math applied to meaningfully summarize that day's data and you can probably get there.

-Matt

 

[Shtiff1]

I borrowed a friends par meter and compared it to my lux meter; looks like lux divided by 46 gives you a close par. I also measured the Parr in my tank and was shocked to see it was only 40 at the sand bed. Maybe this is why I'm getting polyp bailouts. Hmmm...

 

[mcarroll]

I borrowed a friends par meter and compared it to my lux meter; looks like lux divided by 46 gives you a close par. I also measured the Parr in my tank and was shocked to see it was only 40 at the sand bed. Maybe this is why I'm getting polyp bailouts. Hmmm...

That's the conversion factor for your particular light setup. Useful for comparing your future lux readings with others in the form of PAR.

What lux are you reading at the water surface over the "problem" corals?

-Matt

 

[Shtiff1]

4200 the surface

 

[mcarroll]

4200 the surface

10,000 is the low end for "full sun" conditions. 30,000+ is "direct sun".

So, unless you are keeping low-light corals, I'd suggest doubling your light output and see how thing go when you're close to 10,000. For reference, I think my tanks run at about 14,000 lux and 60,000 lux respectively and both grow the same corals.

Make any increases gradually over at least a week - a few weeks would be better.

-Matt