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Unread 03/30/2012, 07:49 AM   #1
chuckdallas
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LUX vs PAR?

I'm an Electrical Engineer (by schooling) but fly planes for the Air Force and American Airlines, so I can't spell PAR vs. LUX.

Back in the first 6 months of my newbie-ness, I bought a Milwaukee Lux meter on a Black Friday special thinking I was getting a PAR meter for a really good deal. I know you can't convert LUX to PAR, but can I measure my lights and then use it to compare with the lights at the Local Fish Stores to see if my lights are stronger or weaker?


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Unread 03/30/2012, 07:54 AM   #2
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You need par.


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Unread 03/30/2012, 09:59 AM   #3
chuckdallas
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Thanks "USC-fan". I understand I SHOULD have bought a PAR meter. Just wondering from the crowd if I measure the LUX of the MHs at the LFS and then measure my LEDs if I can use that as a relative gauge, even though LUX doesn't mix with PAR.


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Lots of equipment left over from the 140 gallon tank teardown. Oct 21st was a sad day. Wife said I would have to get a new wife to get a new tank. I'm sure gonna miss the wife.

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Unread 03/30/2012, 10:59 AM   #4
gbru316
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i believe so, but i'm not 100% sure.

a little FYI, you can purchase the PAR sensor from Apogee and attach it to any multimeter, and multiply the voltage reading by 5 to get PAR in umol/m.

This will save you about $200 vs buying the PAR meter/sensor combo


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Unread 03/30/2012, 12:07 PM   #5
alton
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Since 2004 I have used my LUX/Footcandle meter to check my MH's. I check them when they are new and then around 12 months, if they drop 10% I change them. I have not lost a coral since doing this. PAR meter is better but you can use your LUX meter also to check your lamps life. I have had lamps last 12 to 18 months. I have 3 250w radiums, one I changed because it dropped below the 10%, the other two are less than 5% so I continue using them. No one has ever been able to tell me which one is the new one because your eyes can not tell. I also used it to check my LED light and found that they where going bad the same way and got a new light from the dealer because of it.


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Unread 04/04/2012, 08:16 AM   #6
GeorgeMonnatJr
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LUX is the human eye response and PAR attempts to measure a plant's response to the same light. As you can see in this graph from Aquarium Lighting Measuring Light with a PAR Meter, what is really bright for you (green/yellow) is very dim for a plant. They have almost opposite responses. Lux meters measure the "useless" green/yellow light while PAR, or quantum, meters measure all photons between 400nm and 700nm (I wish they measured/weighted the 500-600nm photons less but nothing's perfect).



That same article states the following for aquatic plants (all in micromols/m2/s):

Low Light: 40-80
Moderate: 80-120
High Light: 120-300

and

normal light ~ 120
high light ~ 200+

Anyone have feedback on that? I used an Apogee SQ-110 yesterday and have about 120-130 where I plan on putting coral. I don't know if that's "normal/moderate" or "high" light, since I've yet to actually have coral in my DT.


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Unread 04/04/2012, 08:30 AM   #7
chuckdallas
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George, it depends on what type of coral you want to grow and how deep your tank is. I'm a softies and LPS kind of guy. I have a large Meat Coral or Open Brain in the far right corner on the sand of my 22 inch deep tank. That corner has 60 PAR, as measured by a fellow reefer's Apogee MQ-200 meter.

The middle section of my tank right under one of the two 60 watt LED fixtures has 100-150 and the top 2-4 inches of the water column has 150-250 depending on if you are RIGHT under the 60 watt rectangular LED fixtures or under the 37 watt Reefbrite strip. I have mushrooms in the quiet left corner (low flow) and they are doing well. I also have a small piece of leather coral about 6-8 inches off the sand about a foot left of the Open Brain.

What kind of coral do you want to keep?


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Lots of equipment left over from the 140 gallon tank teardown. Oct 21st was a sad day. Wife said I would have to get a new wife to get a new tank. I'm sure gonna miss the wife.

Current Tank Info: No tank, no fish, no coral :(
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Unread 04/04/2012, 08:32 AM   #8
chuckdallas
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Can anyone comment on what PAR readings are "normal" for SPS'es? I want to start getting some but I think my 2 X 60 watt LEDs and the 1 X 37 watt Reefbrite strip are not ENOUGH light for SPS'es, even if they are placed high in the tank.


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Lots of equipment left over from the 140 gallon tank teardown. Oct 21st was a sad day. Wife said I would have to get a new wife to get a new tank. I'm sure gonna miss the wife.

Current Tank Info: No tank, no fish, no coral :(
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Unread 04/04/2012, 08:41 AM   #9
gbru316
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Chuck, the apogee reads as much as 50% low when measuring LED PAR because it not calibrated to properly measure response in the blue region. It is meant to measure natural sunlight.

Also keep in mind that PAR is not the only lighting variable. Spectrum is important too. spectrum = quality, PAR = quantity.


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Unread 04/04/2012, 08:42 AM   #10
wayne in norway
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At least 100, and I'm pretty happy with 200 on my sandbed.

As described above LUX should not be the same as PAR, but in practice the PAR readings from my Apogee 200 correlate linearly with my LUX meter, indicating that they are measuring the same thing but putting different values and scales on them. While PAR should not be weighted by the wavelengh (but the Apogee does a little bit) the LUX meter should bed towards green a lot (but is only a little bit).

Both convert photons to electrical charge at the sensor, and scale that same charge to PAR or LUX.


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Unread 04/04/2012, 08:58 AM   #11
GeorgeMonnatJr
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chuckdallas, thank you for the information.

For all, there's a ton of useful information here:

AQUARIUM LIGHTING By Carl Strohmeyer Updated 4/03/12

BTW, I don't disagree with alton, a LUX meter is a useful tool to measure the relative degradation of a light source.


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Unread 04/04/2012, 09:12 AM   #12
GeorgeMonnatJr
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Quote:
Originally Posted by chuckdallas View Post
George, it depends on what type of coral you want to grow and how deep your tank is.
...
What kind of coral do you want to keep?
Sorry, I forgot to answer this in my last post. I plan on starting with zoas then softies and LPS. I'm going to try to take it slow.

Quote:
Originally Posted by gbru316 View Post
Chuck, the apogee reads as much as 50% low when measuring LED PAR because it not calibrated to properly measure response in the blue region. It is meant to measure natural sunlight.
That makes sense, here's Apogee's response graph:



Most "white" LEDs are actually blue LEDs with a white phosphor (called "blue-driven white"), so LEDs have a huge spike around the 450nm graph tick. As gbru316 said, that means the Apogee quantum meter will underestimate the LED's PUR. I use LEDs, so maybe I'm golden



Last edited by GeorgeMonnatJr; 04/04/2012 at 09:13 AM. Reason: typo fix
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Unread 04/04/2012, 09:17 AM   #13
sirreal63
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This should help as a rough guide.



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Unread 04/04/2012, 09:30 AM   #14
GeorgeMonnatJr
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Quote:
Originally Posted by sirreal63 View Post
This should help as a rough guide.
Thank you, that's exactly what I needed.


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Unread 04/04/2012, 09:54 AM   #15
sirreal63
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The only issue I have with that chart is some of those creatures can adapt to very high light, and thrive. Zoa's and most Acro's can do very well in the very high light area. I prefer to think of that chart as a minimum light guide. Clams can be put in as high of light as you can muster.

One problem with buying SPS from your LFS is the light they have them under is often too low, and the majority of what they buy are maricultured corals that are used to the sun, so they are wanting a lot of light and are in decline as soon as you buy them. Frags from local reefers is a better way to go, the corals are already adapted to our lighting. I rarely ever buy SPS from a LFS, the survival rate is too low and I have rarely ever lost a coral as a result of lighting that came from someone else's tank. I am local to Austin as well, and there are some good LFS's to buy from and we have a coral farm in the area too.


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Unread 04/04/2012, 03:02 PM   #16
sahin
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Chuck: I recall a thread some time ago where someone found a decent conversion that will provide very decent figures for Lux to PAR.

Here is the post:
http://www.reefcentral.com/forums/sh...89&postcount=3

From my further reading around on the subject, those who used this sort of conversion factor and compared to a borrowed PAR meter said the conversion was good enough.

There is also an Advanced Aquarist article you can read:

http://www.advancedaquarist.com/2008/2/review

So you can get a decent estimate of PAR with your Lux meter.

I do own a PAR meter myself, I actually own the Apogee MQ-200 PAR meter. Having done tests over the years on MH, T5 and now LED, I can tell you that a PAR of 150-200 is VERY decent for SPS corals (as long as your water quality is in order).

Hope that helps you.


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Unread 04/04/2012, 07:05 PM   #17
DiscusHeckel
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Quote:
Originally Posted by sahin View Post
I do own a PAR meter myself, I actually own the Apogee MQ-200 PAR meter. Having done tests over the years on MH, T5 and now LED, I can tell you that a PAR of 150-200 is VERY decent for SPS corals (as long as your water quality is in order).

Hope that helps you.
The following PAR values have been given to me by a coral farm in the UK. Levels shown are healthy min and max - colouration will vary accordingly. I have also taken PAR measurements with my Apogee quantum sensor. You can't get decent colouration in most SPS, especially Acropora spp with just 150-200 mmol.

#############################################
Pocillapora damicornis 100 - 400 (pink 300-400)
Stylophora pistillata 150 450 (green 150-250, pink/purple 250 - 450)
Acropora nana (300-450)
Acropora blue tip spp2 (300 - 450)
Acropora purple tip (300 -450)
Acropora millepora (300 - 450)
Porites cyclindirica (200 - 400)
Montipora monaseriata (200 - 350)
Montipora digitata (200 - 400)


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Unread 05/17/2012, 10:26 AM   #18
DerrickH
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Using the sensor combined with a multimeter, whats the magic formula? I used this and ended up with 38mv on the sandbed and 62mv on the top of my rockscape. Is it mv x 1.2 x 5 = par?

Edit: For checking LED's not halides or T5's.

52 Cree LED



Last edited by DerrickH; 05/17/2012 at 10:32 AM.
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Unread 05/17/2012, 02:35 PM   #19
wayne in norway
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mv * 5 gives PAR.

It doesn't matter if it's from MH , T5 or LED, where the spectra sits is what counts. Look at the shape of the blue line in the plot in post 12. It shows that btween 525 and 650nm a PAR of one would display at one. If you look at say 450nm on the blue line, the Apogee response correlates to a y of 0.8, so 1 PAR would register as 0.8. Conversely any reading at 450nm needs scaling up by 1/0.8 (1.25).


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Unread 05/17/2012, 02:43 PM   #20
ganjero
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Is LUX degradation proportional to PAR degradation? That should be the question to know if you can use a lux meter to check the life of your bulbs.


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Unread 05/17/2012, 02:57 PM   #21
GeorgeMonnatJr
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Quote:
Originally Posted by ganjero View Post
Is LUX degradation proportional to PAR degradation? That should be the question to know if you can use a lux meter to check the life of your bulbs.
The answer is really, "Maybe." Lux, or luminous flux, is a measure of how well the human eye would respond to the light. The human eye is vastly more responsive to green light.



So really lux is a measure of how "green" a light is. If your bulbs degrade all wavelengths evenly, then yes, a lux meter is a great way to measure degradation. If your bulb doesn't degrade at all in the green, or degrades less in the green than in the other "colors", or if it shifts from another wavelength to green, then it's a horrible relative measure.

PAR is an equal counting of all visible light photons. That's why it's a better measurement of aquarium lights, especially if corals don't care about green but cyano/dino/bryopsis/etc. love green light.



By the way, lux and the human eye response is why a green LED will look super bright to you while a blue or royal blue will look dim. But the blue is probably giving off a lot more energy than the green, which may cause some people to bleach their stuff as they turn up the blue LEDs to make things look as bright as their old MH.


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Unread 05/17/2012, 03:03 PM   #22
alton
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When I checked my tank using a foot candle meter and a PAR meter it was. The difference across all three Radium lamps where proportional.


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Unread 05/17/2012, 03:19 PM   #23
GeorgeMonnatJr
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Quote:
Originally Posted by alton View Post
When I checked my tank using a foot candle meter and a PAR meter it was. The difference across all three Radium lamps where proportional.
In a lot of cases it may be exactly the same. A lot of detectors, including Apogee's quantum sensor, are based on silicon which all have response curves similar to the green one in the previous picture. So if your LUX or PAR sensor isn't calibrated for different wavelengths or weighted differently, it would read just like the green line. Or you have very green light


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Unread 05/18/2012, 06:02 AM   #24
alton
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I ran into an issue with a marineland reef capable led fixture. I checked each of the leds with a foot acndle meter, the best had 3500 ftc, the worst only had 700 ftc. I could not tell the difference between the ones from 1600 to 3500, they looked the same. Only when the leds got below 1000 ftc could you tell they where not as bright(the human eye can not tell). I found this out the hard way the first time I switched to MH, after 8 months my corals started to die and I could not figure it out? Finally got to the the lighting and it had dropped by 50% and in only 8 months. I switched to Reeflux and now Radium and never had that issue again.


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