LUX vs PAR question??

Dave Splain

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Everything I read uses PAR however the only thing I can find are LUX meters. From all the information I read LUX and PAR is not the same thing can somebody make this more simple for me? Can someone also give me the name of the app that gives PAR not LUX readings?

Thank you for your time and information!
 
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Dr. Reef

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you are right LUX and PAR are not the same.
LUX meters measure the amount of usable light for humans while PAR meters measure a spectral range including how many photons fall on the the plants in 1 sec within that spectral range.
i am not sure of an app as i have a PAR meter. i am sure someone else will chime in.
 

jda

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You can use a LUX meter and convert it to PAR. I do not know of any LUX meters will go under the water, though.

Both are equally good and worthless at the same time. Both only capture parts of the visible spectrum and corals use waves below and above what we can see. However, either can be a good guide when used with other things like spectrum charts and stuff so that you can normalize for the testing/reading difficulties.

Some of the common PAR meters are Apogee 210, Apogee 510/520 and Seneye. They are more than a normal LUX meter that is around $20-25.
 

oreo5457

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Everything I read uses PAR however the only thing I can find are LUX meters. From all the information I read LUX and PAR is not the same thing can somebody make this more simple for me? Can someone also give me the name of the app that gives PAR not LUX readings?

Thank you for your time and information!
20170823111939567.jpg



Think of a LUX meter as measuring a subset of "PAR"..


LUMENS measure of photons in the range that the human eye is most sensitive to.
See bell curve above.

PAR measure of the photons over the range of 400-700 (most common).

LUX = lumens/area/second
PPFD = PAR/area/second

PAR is often substituted for PPFD..
 

mike werner

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I only measured par because it is the standard of reefers for the most part.I wanted to make sure I was not above or below the suggested levels. now I just go off the reaction of the corals and have not found a reason to adjust things.
finding that sweet spot with lighting is easy but takes a little time.i'm sure I sound like the broken record but"go slow" barrow a meter if available and see what ya have.
 

Scrubber_steve

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Everything I read uses PAR however the only thing I can find are LUX meters. From all the information I read LUX and PAR is not the same thing can somebody make this more simple for me? Can someone also give me the name of the app that gives PAR not LUX readings?

Thank you for your time and information!
You can put your lux meter in a zip lock bag & use it under water.
There is a conversion from lux to par, but I'll have to search for it.
Another way to get a guage is if your LPS will allow you to get a reading on one of their reef tanks using your lux meter.
 

oreo5457

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You can put your lux meter in a zip lock bag & use it under water.
There is a conversion from lux to par, but I'll have to search for it.
Another way to get a guage is if your LPS will allow you to get a reading on one of their reef tanks using your lux meter.
lux2par.JPG

https://www.apogeeinstruments.com/conversion-ppfd-to-lux/
Dividing LUX by 60 to 70 is pretty standard..

You would think it gets tricky w/ sooo much blue but for some reason..isn't so bad..
 
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Dave Splain

Dave Splain

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mcarroll

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(paraphrasing from the Beginners Lux article...)

Conversions are based on the light source being measured....so every light source has it's own par : lux conversion factor.

Most reef lights are very similar in their overall color profile thanks to similar combo's of LED's being used to meet a fairly common "20,000K" color. So most reef lights will fall into a pretty narrow range of conversion factors.

IMO, if you can't get a PAR meter to "calibrate" your lux meter, then sunlight's conversion factor of 50 is ideal.

Mainly since it lets me do the math in my head. :) :) :) But also, I regard all light measurements as very approximate whether they come from a PAR meter or a lux meter, so the difference (vs 60 or 70) doesn't matter too much in practice.
 

oreo5457

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Bump.

Links are broken. Anyone using a lux meter to convert to PAR? I just want really ballpark results. Thansk!
In the article is says you can convert LUX to PAR as stated below. (estimate conversion).

...it is possible to convert lux measurements to PAR values. Use these results with some caution - in most cases it would be safe to assume the results will be low.
•Divide blue (450nm) LED Lux by 69
•Divide white (7,300 K) LED Lux by 45
•Divide blue (450nm)/white (7,300 K) combination LED (2:1 white/blue ratio) Lux by 67

Dividing by 60 to 70 is pretty "standard".

Advancedaquarist is all screwed up..thinks it's a security cert. issue.

anyways one can use the"Wayback Machine"

 
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chipmunkofdoom2

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The conversion factors I've seen are 40 for MH, 50 for T5, and 60+ for LED. I set up a spreadsheet where I input my lux reading to get a general idea of the PAR:

LuxChart.png


The 60 - 75 range is appropriate for LEDs. The more blue you use, the higher up the range you go. I don't know the relative blue to white ratio I use, so I show all of these conversion factors and an average of the four. I treat the "average" as my actual PAR number, but seeing the min and max are useful to get an idea of the probable range of values.
 
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oreo5457

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The conversion factors I've seen are 40 for MH, 50 for T5, and 60+ for LED. I set up a spreadsheet where I input my lux reading to get a general idea of the PAR:

LuxChart.png


The 60 - 75 range is appropriate for LEDs. The more blue you use, the higher up the range you go. I don't know the relative blue to white ratio I use, so I show all of these conversion factors and an average of the four. I treat the "average" as my actual PAR number, but seeing the min and max are useful to get an idea of the probable range of values.

Conversion factors should be based on spectrum not type of light.
A 6500K t5 will have a very different conversion from an "actinic" T5.

I suppose ther are some things to consider , like MH's huge and pure LUX green spike in the spectrum.
 

chipmunkofdoom2

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Conversion factors should be based on spectrum not type of light.
A 6500K t5 will have a very different conversion from an "actinic" T5.

I suppose ther are some things to consider , like MH's huge and pure LUX green spike in the spectrum.

Well yes, but how on Earth is the average hobbyist supposed to calculate the exact color temperature or spectrum of their light? There's no master database that exists of lux to PAR conversion factor for every single type of lighting used over reef tanks. Even if there was, it wouldn't be possible to derive the exact spectrum of the light hitting your tank. Not unless you run one type of MH or T5 bulb or only run a single LED spectrum.

If you or anyone else would like to try to derive the exact spectrum for your specific light so that you can get a perfect conversion factor, be my guest. I don't think that's possible with an accuracy that would be meaningful to most hobbyists. Generalized conversion factors are a quick and reasonably accurate way to get an estimate of PAR in your tank with a lux reading. If you need an exact conversion factor for your lux reading based on your specific light and spectrum, buy or rent a PAR meter. This is really the only meaningful difference between the two anyway. Lux meters measure intensity, PAR meters measure intensity and apply a correction factor based on the specific spectra measured.
 

chipmunkofdoom2

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@oreo5457 @chipmunkofdoom2

Very helpful info thanks. Can you link lux meter you use? I cant find any waterproof, do you put into plastic bag? Do you even use it under water? Do you need to correct for water imersion or anything?

Thanks!

I don't see the one I have for sale anymore. It was just a cheap $10 - $15 one from Amazon. Most of the cheap ones probably work okay. Just make sure the reviews are good and that it can measure up to 100,000 lx.

I don't test mine underwater. The last time I adjusted my light I measured lux during a water change. I measured at various water levels and recorded the results. I don't keep any corals in the bottom of my tank, so I really don't measure below half way. Water will probably change the intensity, but I don't need reading that specific. I just need to know am I blasting my acros with 600+ PAR or am I in the 200 ballpark.
 

oreo5457

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Well yes, but how on Earth is the average hobbyist supposed to calculate the exact color temperature or spectrum of their light? There's no master database that exists of lux to PAR conversion factor for every single type of lighting used over reef tanks. Even if there was, it wouldn't be possible to derive the exact spectrum of the light hitting your tank. Not unless you run one type of MH or T5 bulb or only run a single LED spectrum.

If you or anyone else would like to try to derive the exact spectrum for your specific light so that you can get a perfect conversion factor, be my guest. I don't think that's possible with an accuracy that would be meaningful to most hobbyists. Generalized conversion factors are a quick and reasonably accurate way to get an estimate of PAR in your tank with a lux reading. If you need an exact conversion factor for your lux reading based on your specific light and spectrum, buy or rent a PAR meter. This is really the only meaningful difference between the two anyway. Lux meters measure intensity, PAR meters measure intensity and apply a correction factor based on the specific spectra measured.


Point was the more blue in the spectum (spectrum charts for most things are readily available the lower the divisor.

Start w/ 60 as an average light (blue plus some white, i.e AB +, t5 blue plus, 1400k metal halides (though MH's are notoriously mis-labeled)
Decrease from 60 as one adds blue.
According to this "pure actinic" LED @450nm
1000LUX = 115.55 "PAR" (really PPFD) Divide by 8.6 :eek:

Need to just gues the best one can based on the best info one assumes.. ;)
LUX meters measure a subset (visual sensitivity) of PAR heavily center weighted on green w/ tailing off as one goes to red or blue
 

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