Standard Bulb for PAR Meter Calibration - The Planted Tank Forum
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post #1 of 47 (permalink) Old 05-30-2015, 08:03 PM Thread Starter
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Standard Bulb for PAR Meter Calibration

People who make their own DIY PAR meter have a difficult time adjusting the calibration so the meter reads correctly, unless they have access to an Apogee PAR meter. After a PM discussion with Quizcat I decided to see if a specific manufacturer's CFL bulb of a specific wattage and color temperature could be used as a "standard light", giving a known PAR reading at a specific distance. With this one could set up their PAR meter at that distance from the bulb and adjust the readout to give the known PAR.

I had a new GE CFL bulb on hand, so I made a fixture that let me use an Apogee PAR meter, borrowed from Plantbrain, to determine the PAR vs distance from a specific location from the bulb. The bulb is: (from Ace Hardware)


The fixture used to measure PAR at a specific location relative to the bare bulb is:


The fixture is a spare table lamp, with a wood bracket that clamps onto the lamp below the bulb, with the bracket adjustable in distance from the face of the bulb in 1 inch increments, and the Apogee sensor attached with the screw it comes with to a piece of aluminum angle attached to the bracket. The sensor is aimed at the middle of the bulb, and the distance is from that face of the bulb to the sensor white diffuser.

I warmed up the bulb for 15 minutes, then started taking PAR readings. After I took the last of 5 readings I repeated the first and last reading. All read the same, except the first one which was within 1 of the same reading. All readings were done in 30 minutes.

Here is a graph of the results:


This is plotted on loglog graph paper, which makes curves plot as straight lines, making it more accurate. You can see that all of the data points come very close to being on the line.

If you want to use this, use a bare bulb identical to this one, not just similar, or made by a different manufacturer. Aim your PAR meter at the middle of the side of the bulbs coiled tube and measure the distance from the bulb surface and the diffuser on your PAR meter. Use the value of PAR from the chart as what your meter should read.

After discussing this with Plantbrain (Tom Barr) he convinced me that using an ordinary incandescent bulb would work better. Li-Cor, who make the best PAR meter in the world, recommends using an incandescent bulb to check the calibration of their PAR meters. You get a new bulb, measure the PAR at a specific distance from that bulb with their PAR meter, record that number. Then carefully store the bulb and use it again and again every year or so to verify that the meter continues to read the same.

Incandescent bulbs are just very hot wires radiating light (and heat) as a "black body". There are no quirks in the spectrum of that light, which is a standard black body spectrum. Fluorescent or LED lights all have a complex spectrum, with peaks and valleys, and two different bulbs might have some differences in the heights of those peaks and valleys, so they can't be assumed to all be the same, nor can you assume that aging will not affect that spectrum. It doesn't matter that the incandescent bulb spectrum is much different from our aquarium light spectrums. (This I'm still a bit wary of.)

If anyone thinks this is a worthwhile effort I will try to find a cheap, readily available to everyone incandescent bulb to try with this. Or, perhaps someone knows of a better, more available CFL bulb to try.

Hoppy
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post #2 of 47 (permalink) Old 05-30-2015, 09:01 PM
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Cool idea. I'll be watching.
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post #3 of 47 (permalink) Old 05-30-2015, 09:02 PM
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Any bulb can be used to compare one sensor to another.. bigger problem is knowing if either is "right"..



Personally using a 12v halogen on a switching power supply will "hopefully" keep the output stable.
Using an old computer power supply and a quartz bulb is the simplest and relatively more consistent method..
and Hoppy, a good set of filters w/ known spectrum can be used to track "anomolies" in one sensor vs another..

Running lamps on line voltage is problematic from surges dropouts ect..

https://www.bulbamerica.com/products...FZGLaQoddTgApA

Actually use a Zenon bulb:


https://www.1000bulbs.com/product/67...FVNufgodYSQASA

Arguably running a constant current 2A driver might be a bit better.......

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Last edited by jeffkrol; 05-30-2015 at 09:17 PM. Reason: edit
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post #4 of 47 (permalink) Old 05-30-2015, 09:26 PM
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Quote:
Originally Posted by jeffkrol View Post
Any bulb can be used to compare one sensor to another.. bigger problem is knowing if either is "right"..



Personally using a 12v halogen on a switching power supply will "hopefully" keep the output stable.
Using an old computer power supply and a quartz bulb is the simplest and relatively more consistent method..
and Hoppy, a good set of filters w/ known spectrum can be used to track "anomolies" in one sensor vs another..

Running lamps on line voltage is problematic from surges dropouts ect..

https://www.bulbamerica.com/products...FZGLaQoddTgApA

Actually use a Zenon bulb:


https://www.1000bulbs.com/product/67...FVNufgodYSQASA

Arguably running a constant current 2A driver might be a bit better.......
Ya but,,,, doesn't the guy at home have to easily duplicate the result?
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post #5 of 47 (permalink) Old 05-30-2015, 10:03 PM Thread Starter
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This only works if those who are making a PAR meter have access to one of the bulbs used, and at a price that is far less than a good PAR meter. If that bulb costs $5 I think the idea works well. It it costs $15 I suspect that would discourage anyone from using this method.

I know that CFL bulbs, with a color temperature in the range of 6500K, will work for either an Apogee meter or a DIY PAR meter made similar to what I was making or what mistergreen makes. I'm not yet convinced that an incandescent bulb will do it, even though it works fine for re-checking your PAR meter once it is adjusted to read correctly. If there is a problem with that use it is the probable very low PAR reading you would get if you used it like I show here. At low readings there is a big inherent error just from the inability to read enough significant numbers.

What is a widely available CFL bulb, 6500K, that costs under $10 per bulb?

Hoppy
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post #6 of 47 (permalink) Old 05-30-2015, 10:14 PM
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Hoppy,

In my particular case, I've been using the Sylvania brand CFLs that have the spiral elements, the ones that advertise that they put out 5 Watts or 13 Watts, but claim to deliver more "Light" than that, I suppose more light with respect to lumens than the wattage ratings would otherwise be anticipated to deliver from a conventional/incandescent bulb.

Here are the links to the exact ones I'm using via Lowes.com regarding the 5-Watt and the 13-Watt Versions:

Here is the link on Lowes.com to the 5 Watt ($4.57 each):
http://www.lowes.com/pd_47188-3-2690...ania+cfl+6500k

Here is the link on Lowes.com to the 13 Watt ($6.98 each):
http://www.lowes.com/pd_302424-3-269...d=3202351&Ntt=

Sylvania also manufactures a 23 Watt version, and here is the link to that one as well, but I haven't used it because I figured that the lumens rating is too high for my tanks, which are small, only 10 gallon, 20 gallon, and 28 gallon (Cube).

http://www.lowes.com/pd_302257-3-269...ania+cfl+6500k

The 23-Watt ($10.61 each) might be applicable too your request for a listing. I'm not advocating the use of CFLs particularly for use in aquarium light fixtures, but I do like that they're at least in the light color range that has relevance to aquarium lighting, versus the incandescents. I am curious to know if the CFLs can be used to reliabily calibrate the CEPs, and whether those readings can be relied upon to design other more sophisticated fixtures to PAR.

I recommend testing these models above because they are commonly available, from a well known manufacturer, under or about at the $10.00 amount Hoppy mentioned depending on size, and other forum members can easily obtain them throughout the entire country.

The other thing is they have a very small footprint, and I've been able to incorporate them into fixtures very easily. But, I have to admit, I haven't tried some of the other brands that might be out there. But, these in particular do burn cool, and can be easily incorporated into a home-made fixture. I'm sure there are much more sophisticated fixtures out there that are being built, ones that are really far superior than just a couple of CFLs. But, if we are trying to establish PAR for calibration of a CEP, and that PAR number from the CFLs can be established to be consistent between other types of bulbs and fixtures, using a commercially produced PAR meter, then we have a very convenient way of getting "close" with respect to calibration of the CEP without having to have a commercially produced PAR meter in our possession, or having to send our CEPs off to those members that might have a commercially produced PAR meter.

In the interest of being totally thorough, it will be necessary to test between several of the same model CFLs to establish a consistency level between CFL bulbs of the same model, but also between Lot Numbers, in order to establish a consistency expectation between CFLs of the same brand. And, to be really enterprising, perhaps comparing CFL PAR using a high quality commerically produced PAR meter to other types of light emitters.

We'll probably have to factor-in some kind of (+) or (-) statistcal deviation. But, I am hopeful the CFLs are relatively consistent between lot numbers, etc...and that the PAR readings from the CFLs are consistent with other types of emitters. If so, then theoretcially we could be relatively confident that we'll be able to calibrate our CEPs based on particular models of CFLs that have been tested for consistency, provided we use the same testing methodology by which Hoppy's testing process is conducted. And, of course, there is also the inconvenience of having to re-test when new designs come on the market, which is bound to happen.

I would also suggest that brand new bulbs be used to calibrate at all times, unless we can somehow forecast when the consistency in the bulb's life begins to drop off. If we can establish a length of hours that the bulb's performance is on "PAR," no pun intended, then we could conceivably save bulbs year after year for calibration purposes. But, even if we have to buy a new bulb each year, costing $5.00-$10.00, it's not particularly expensive to know that our CEPs are on PAR. But, having to buy a new bulb year after year, when there is a high likelihood that new models will emerge on the market that are untested, makes saving the bulbs for many years of use much more attractive.

I think it would be very interesting to see what the deviation is between different brands, such as Hoppy's GE, versus the Sylvanias I mentioned. It would really be quite a revelation if PAR readings are also consistent between various brands and lot numbers of CFLs. If that turns out the be the case, then the likelihood of new models throwing a wrench into past testing is significantly reduced.


Quote:
Originally Posted by Hoppy View Post
This only works if those who are making a PAR meter have access to one of the bulbs used, and at a price that is far less than a good PAR meter. If that bulb costs $5 I think the idea works well. It it costs $15 I suspect that would discourage anyone from using this method.

I know that CFL bulbs, with a color temperature in the range of 6500K, will work for either an Apogee meter or a DIY PAR meter made similar to what I was making or what mistergreen makes. I'm not yet convinced that an incandescent bulb will do it, even though it works fine for re-checking your PAR meter once it is adjusted to read correctly. If there is a problem with that use it is the probable very low PAR reading you would get if you used it like I show here. At low readings there is a big inherent error just from the inability to read enough significant numbers.

What is a widely available CFL bulb, 6500K, that costs under $10 per bulb?

Last edited by Quizcat; 05-31-2015 at 02:46 AM. Reason: comments...
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post #7 of 47 (permalink) Old 05-31-2015, 02:00 AM Thread Starter
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I think I will get a pair of the Sylvania 23 watt ones, since the lower wattage ones will produce PAR readings too small to maintain any accuracy. With 2 of them I can see if they both produce the same PAR. If they don't the idea probably won't work well.

I'm still thinking about the incandescent bulbs.

It is pretty cheap to get data on a bulb, so maybe having this data for several different bulbs is a good idea. I can always use the bulbs in lamps later.

Remember, this tells us almost nothing about using these bulbs to light a tank, since I'm intentionally not using any form of reflector, and I'm measuring the PAR much closer to the bulb than the substrate would be in almost all tanks.

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post #8 of 47 (permalink) Old 05-31-2015, 02:39 AM
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True, but it may give us a standard to go by with respect to calibration of CEPs if your commercially produced PAR meter returns consistent results between two bulbs. While the CFL may or may not be the best choice to use in lighting a tank, a reliably calibrated CEP, or commercially produced PAR meter, is a great tool to assist us in designing the best lighting we can, whether that turns out to be LEDs, or whatever.

Since most of us don't want to purchase a $300-$400 commerically produced PAR meter, an accurately calibrated CEP from a $10.00 CFL is a fantastic alternative, and especially if we can save it for calibration year after year.

I appreciate your efforts very much!


Quote:
Originally Posted by Hoppy View Post
I think I will get a pair of the Sylvania 23 watt ones, since the lower wattage ones will produce PAR readings too small to maintain any accuracy. With 2 of them I can see if they both produce the same PAR. If they don't the idea probably won't work well.

I'm still thinking about the incandescent bulbs.

It is pretty cheap to get data on a bulb, so maybe having this data for several different bulbs is a good idea. I can always use the bulbs in lamps later.

Remember, this tells us almost nothing about using these bulbs to light a tank, since I'm intentionally not using any form of reflector, and I'm measuring the PAR much closer to the bulb than the substrate would be in almost all tanks.
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post #9 of 47 (permalink) Old 05-31-2015, 02:55 AM
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Quote:
Originally Posted by Quizcat View Post

Since most of us don't want to purchase a $300-$400 commerically produced PAR meter, an accurately calibrated CEP from a $10.00 CFL is a fantastic alternative, and especially if we can save it for calibration year after year.

I appreciate your efforts very much!

The current bar is $200 plus a laptop..
http://www.aquariumspecialty.com/bio...h-15-usb-cable

Quote:
A fully equipped PAR Meter from Apogee presently costs just south of $400 for the entire assembly but Apogee also offers up bare quantum sensors for measuring Photosynthetically Active Radiation for just $155.

Presumably, a standalone USB PAR meter could be offered up for a reasonable $200 and paired up with our own laptops and computers, a feature which would further streamline the process of logging different PAR data points. The Apogee USB PAR meter in the U.S. is a collaboration with Aquarium Specialty’s Biotek Marine brand
Read more: http://reefbuilders.com/2014/12/05/a...#ixzz3bgIVaenb

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post #10 of 47 (permalink) Old 05-31-2015, 03:49 AM
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Yep, I was thinking of the ones I saw online that were self contained for around $360.00. I have seen a few advertised that are quite a bit less than certain other models I've looked at. I'm not sure if there's a performance difference between them, or whether most of the lesser expensive ones perform consistent with the higher priced ones or not.

I watched the video at the link you sent. Pretty cool!!! They are getting more affordable aren't they...

I can't justify spending money on the higher priced ones or the lesser priced ones. One thing is for sure, the CEP is truly affordable for anyone.


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post #11 of 47 (permalink) Old 05-31-2015, 05:29 PM
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Yes, but once you can establish that PAR is consistent at those distances on your chart, then PAR should be whatever PAR is at greater distances, all-be-it most likely at a reduced number.

When I tested using the CEP on my 10 gallon tank, which has (2) 13 watt CFLs contained in a converted Perfecto light housing, bulbs oriented horizontally in the fixture housing, with aluminum reflective tape as a reflector adhered behind the bulbs to the original housing, a housing converted from florescent to standard bulb recepticals, the numbers being returned at 8" of depth, were pretty respectable, high 60's to low 70's depending on where the sensor was in the tank. Since you had no reflector system as part of your test fixture, your numbers from the CFL seem like they could be pretty reliable, in the 30s to 40s, not to mention that my readings were taken under water, from bulbs that were horizontally oriented, and your readings were taken out of water.

Thost readings I took previously were taken before I had the meter calibrated properly, so I have to confirm the numbers above once I get the meter back from Mistergreen after his "official" calibration with a commercially produced PAR meter. But, based on what Mistergreen reported to me this morning, the calibration added another 30 points to the PAR readings I took before his "official" calibration, which were high 30's to low 40s based on noon day sun calibration.

During my "unofficial" calibration, I had calibrated to 1950 PAR from the mid-day full sun at noon. So, the numbers I am estimating above, result from Mistergreen adding about 30 points to the POT position, adding about a 1/4 turn, versus the calibration I made based on the noon-day sun.

Now, whether my CFLs are delivering the proper color temperature in the correct dosages is the question. But, all my tanks are fresh water tanks, and I would suspect that at 6500K that they're fine.

If the tanks were marine tanks, with coral, etc..., then I can see where the color temperature would be much more of an issue. I do get some brown algae in all my the tanks, but according to my readings with the CEP, the light factor isnt the issue, probably more to do with phosphate levels due to my water quality. Well, not my water quality, but the water quality in my neck of the woods. I do routine and frequent water changes to my tanks, but the algae usually returns over the course of several months, even after I clean it up thoroughly, and change the water frequently, meaning every week of so. Anyway, I don't think the Algae is a result of the CFLs because I am also experiencing that problem from the LEDs as well. Probably phosphates. It's not likely nitrates (usually under 10ppm), because they read low when testing for them.

The PAR readings on the RGBW+W(Warm White/Cool White) LED light fixture, and the SMD2835 fixture (all Cool White 6500K), before Mistergreen's calibration, returned readings of 12 Par to as much as 18 PAR. When you add Mistergreens additional adjustment to the POT, the LED strip lights should be delivering enough PAR theorectically for low to medium light plants using LED strip lights, 40 to 50 PAR.

Quote:
Originally Posted by Hoppy View Post
...and I'm measuring the PAR much closer to the bulb than the substrate would be in almost all tanks.

Last edited by Quizcat; 05-31-2015 at 05:48 PM. Reason: comments...
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post #12 of 47 (permalink) Old 05-31-2015, 06:44 PM
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The sun is alway a good standard but indoor light takes more finesse. 30 micromol difference can mean low light and medium light but in sunlight, it doesn't make much difference.

I think having a PAR meter to calibrate against will give you the most accurate results. But having known values to lightbulbs is good enough or even just calibrate against the resistor values given it's built the same as the CEP.
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post #13 of 47 (permalink) Old 05-31-2015, 09:50 PM Thread Starter
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This is proving to be as complicated as I thought it might be. Today I bought a 2 bulb package of the Sylvania "100 watt" (23 actual watts) bulbs, and measured the PAR for both bulbs after a 30 minute warm up. The two bulbs differed by about 10%, which surprised me. So, I let one bulb "warm up" for another 30 minutes and it then agreed with the other bulb. The PAR output seems to oscillate slowly as the bulb warms up, or burns in. I'm now running both bulbs in lamps and will let them run for about 4-5 hours before trying this again. Maybe this can only work if the bulbs are run in for hours before using them. And, maybe the manufacturing tolerances are only good enough to keep them within 10+% of each other.

The Sylvania bulbs, at 23 watts give more PAR than the GE bulb at 26 watts!

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post #14 of 47 (permalink) Old 05-31-2015, 10:50 PM
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How do you calibrate against the resistor value of a bulb? Can you elaborate with "how to" specifics please? Just curious...Do you just take an Ohm Meter reading between where the bulb is iinstalled in the circuit to get the resistance...Then, how do you convert that resistance number to calibrate the PAR meter? If that would work, then one could measure the resistance of a random individual bulb that one might acquire, calibrate to that each time based on the individual bulb performance, and the slight PAR difference between bulbs pulled from the shelf really wouldn't matter.

Quote:
Originally Posted by mistergreen View Post
...or even just calibrate against the resistor values given it's built the same as the CEP.

Last edited by Quizcat; 05-31-2015 at 11:44 PM. Reason: comment...
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post #15 of 47 (permalink) Old 05-31-2015, 11:44 PM Thread Starter
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Quote:
Originally Posted by Quizcat View Post
How do you calibrate against the resistor value of a bulb? Can you elaborate with "how to" specifics please? Just curious...Do you just take an Ohm Meter reading between where the bulb is iinstalled in the circuit to get the resistance...Then, how do you convert that resistance number to calibrate the PAR meter? If that would work, then one could measure the resistance of an individual bulb that one might acquire, calibrate to that each time based on the individual bulb, and the slight PAR difference between bulbs pulled from the shelf really wouldn't matter.
I think that is referring to the resistor in the CEP meter that sets the sensitivity of it.

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