Why all the talk about LUX?

[Daniel@R2R Verified Admin]

Basically, the cheap lux meters we use could be 20% off.

This is another concern I have with the free/cheap meters.

 

[Daniel@R2R Verified Admin]

I appreciate the data given so far in this thread. It let's me see that I definitely need to read up more on light readings and specifically how LUX and PAR differ from one another. I notice Dana Riddle is quoted quite a bit (and he's certainly far more knowledgeable than I). Is he the only one doing anything on this? Has anyone else corroborated his research? Has anyone (at a research level) disagreed with his findings?

 

[gus6464]

People who love to quote Dana Riddle on here about Lux meters on this board love to omit his statement that a conversion factor is needed for every wavelength and source of light being measured. A 6500K LED does not have the same conversion factor as a 4000K one. A Lux meter reads light like the human eye, all in the green and almost none in the blue, violet, and red. You are playing with fire not knowing the conversion factors and the ones Riddle has published are completely outdated by now.

Then there's the whole off yeah you want 30000 to 60000 Lux on your tank. That is a random blanket statement that doesn't in the slightest take into account the source and wavelengths being measured. This is an example of why Lux is useless for our purposes.
http://www.danireef.com/2013/11/28/led-fixture-sicce-gnc-am-466-in-depth-review/

Notice the Lux reading of 19000. Some have pointed out before that this reading is too low. Well guess what? The PAR reading is 512.

An ATI True Actinic bulb puts out 500 Lux but over 360 PAR.

It is so easy to make a Lux meter throw off a super low number when in fact you are pushing tons of PAR.

Whenever the LUX meter evangelists come out of the woodwork ask them to give you the correct conversion factors for your specific light source and wavelengths. You will not get that number from them.

 

[Phil Cusimano]

Maybe it's bc of the apps that people are talking about it more, but in my understanding of photosynthesis, knowing LUX isn't really helpful because the amount of USEFUL light (based on PAR) is not the same under every light bulb, so a coral going under X amount of LUX in 1 tank may be getting a total different amount of PAR than a coral under the same LUX rating in another tank.

Very true, I've always used Par. Not a fan of LUX at all

 

[madweazl]

People who love to quote Dana Riddle on here about Lux meters on this board love to omit his statement that a conversion factor is needed for every wavelength and source of light being measured. A 6500K LED does not have the same conversion factor as a 4000K one. A Lux meter reads light like the human eye, all in the green and almost none in the blue, violet, and red. You are playing with fire not knowing the conversion factors and the ones Riddle has published are completely outdated by now.

Then there's the whole off yeah you want 30000 to 60000 Lux on your tank. That is a random blanket statement that doesn't in the slightest take into account the source and wavelengths being measured. This is an example of why Lux is useless for our purposes.
http://www.danireef.com/2013/11/28/led-fixture-sicce-gnc-am-466-in-depth-review/

Notice the Lux reading of 19000. Some have pointed out before that this reading is too low. Well guess what? The PAR reading is 512.

An ATI True Actinic bulb puts out 500 Lux but over 360 PAR.

It is so easy to make a Lux meter throw off a super low number when in fact you are pushing tons of PAR.

Whenever the LUX meter evangelists come out of the woodwork ask them to give you the correct conversion factors for your specific light source and wavelengths. You will not get that number from them.

PAR meters use correction factors when measuring various wavelengths as well. All of it seems a bit crazy to me.

 

[gus6464]

PAR meters use correction factors when measuring various wavelengths as well. All of it seems a bit crazy to me.

Not nearly the same. You rarely need to do a conversion factor on a PAR meter on a single wavelength basis. Plus the cheaper PAR meters like Apogee now have an updated unit whose quantum response is super close to the LiCor.

The only factor required on an Apogee MQ-500/SQ-520 is the immersion effect factor and that is because the sensor does not have a clear cover but frosted.

 

[Coastie Reefer]

All I know is that I get a reading of anywhere from 90k-100k LUX at about 14 inches under my old school BoostLED 135w fixture that I have over my frag tank. Below is the old PAR graph they used to have on their site. Best I can read is 225 PAR at 20". This photo taken from their old FB page as BoostLED is no longer in business.

I don't know what to think...

 

[Daniel@R2R Verified Admin]

a conversion factor is needed for every wavelength and source of light being measured. A 6500K LED does not have the same conversion factor as a 4000K one. A Lux meter reads light like the human eye, all in the green and almost none in the blue, violet, and red. You are playing with fire not knowing the conversion factors and the ones Riddle has published are completely outdated by now...

...Notice the Lux reading of 19000. Some have pointed out before that this reading is too low. Well guess what? The PAR reading is 512.

An ATI True Actinic bulb puts out 500 Lux but over 360 PAR.

It is so easy to make a Lux meter throw off a super low number when in fact you are pushing tons of PAR.

THIS! This is my understanding of the way all of this works. It seems that measuring levels of LUX doesn't actually measure what's important and may actually give a false understanding of things that aren't important. I'm well aware that I'm no expert, so I'm open to being corrected, but if what I do know is correct, LUX readings may be high when PAR is still low and LUX may be low and PAR actually still be high. So I'm missing how this ends up being really helpful.

I do totally understand the "better than nothing" argument, and I definitely agree that it IS better than nothing (unless it gives a false sense of security to someone who doesn't understand it, and then it might actually be WORSE than nothing). LUX (again, in my understanding) can help to quantify the light intensity that we see, but it will not tell us how much USEFUL light is actually being transmitted to our corals.

If the conversion factors can be proven to work and a method can be used t insure precision in measuring the LUX of useful light, then that may be worth explaining and perhaps research can provide ways to do this (or maybe it already has and I'm unaware). I need to read more...

I still say that an article explaining the differences and some detailed explanation of how LUX should be understood in relation to PAR (and both of these in relation to corals and other photosynthetic marine life) would be useful. It would need to sufficiently explain what LUX readings can do and what they can't (same for PAR). Ultimately, it would give a fair and balanced way of looking at this conversation...at least that's what I'd like to read.

 

[madweazl]

Isnt "useful" light by definition, PUR?

 

[gus6464]

Isnt "useful" light by definition, PUR?

Yes. PUR is the wavelengths plants and corals use mainly for photosynthesis. This is 400-500nm and 600-660nm. 500-600nm is used purely for aesthetics as most don't want a super blue tank. Now this is where it get's tricky. With the advancements in LED diodes it is insanely easy to have a reef light that is 99% diodes in the 400-500nm range and then have that 1% be the aesthetics diode. How? Lime and Mint. Because lime and mint have such massive output in green and yellow but it being insanely narrow bandwidth you can make a super blue tank look whiter with just a tiny bit of it. How much LUX do you think a light like this will put out? Almost nothing. So now we have something called very high PUR and PAR/no LUX.

BTW that light above has ZERO white LEDs but will still look white.

 

[Daniel@R2R Verified Admin]

Isnt "useful" light by definition, PUR?

Maybe...and based on what I've read and understand (sometimes what I read and what I understand are not the same thing...LOL), in theory PUR is more precise than PAR...but PAR is also defined as being light that is useful for photosynthetic organisms. So, the term "useful" can be applied to PAR in a way that it cannot be applied to LUX. Again, this is my understanding, and I am open to correcting that understanding if need be (hence, this thread).

 

[NCreefguy]

The only factor required on an Apogee MQ-500/SQ-520 is the immersion effect factor and that is because the sensor does not have a clear cover but frosted.

This is the par meter that I have. I have read that the correction factor is 1.32 or 32% for this meter due to the immersion effect factor. So to make sure I'm understanding this correctly, I take the readings that I get and add 32% to get my actual par levels?

 

[gus6464]

Maybe...and based on what I've read and understand (sometimes what I read and what I understand are not the same thing...LOL), in theory PUR is more precise than PAR...but PAR is also defined as being light that is useful for photosynthetic organisms. So, the term "useful" can be applied to PAR in a way that it cannot be applied to LUX. Again, this is my understanding, and I am open to correcting that understanding if need be (hence, this thread).

PAR is basically measure of flat quantum response between 400-700nm. This means that photon output at 550nm is measured the same as 450nm and 650nm. PAR takes everything in the range and spits out a number. PUR or photosynthetic usable radiation is the photon output measurement only required for photosynthesis.

Dana Riddle has measured PUR output for some bulbs. So for example a UVL Actinic is 99% PUR output. A blue bulb like the Blue+ because of it's peak in green region is something like 85% PUR. So the fact that the actinic bulb is weaker in PAR is offset by the fact that 99% of it's output is absorbed by corals.

 

[gus6464]

This is the par meter that I have. I have read that the correction factor is 1.32 or 32% for this meter due to the immersion effect factor. So to make sure I'm understanding this correctly, I take the readings that I get and add 32% to get my actual par levels?

Correct.

 

[ksc]

On the new mq500 you add 32% if you are taking readings underwater. If taking readings in air you don't add anything.

 

[NCreefguy]

Perfect! Thank you

 

[Brew12]

PAR: Photosynthetically Active Radiation - it is a measurement of the intensity of lighting in the range that causes photosynthesis.
Lux: Latin for light - equal to 1 lumen spread over 1 meter
Lumen: The amount of light given off by one candela.
Candela: The visible light given off by one unfiltered candle

So, Lux is a unit of measure of all visible light in the spectrum. PAR only reads light in the 300nm-700nm range. Lux concentrates at the 550nm range.

I'm not even sure where I am going with this anymore! Other than that as we try to convert PAR to Lux, the conversions only hold true for certain light wavelengths so rough estimations are about as close as we can come. Theoretically, an LED that emitted in the 1100nm range would have a slightly lower Lux than our eye would perceive but wouldn't have any PAR.

 

[saltyfilmfolks]

How much LUX do you think a light like this will put out? Almost nothing. So now we have something called very high PUR and PAR/no LUX.

I don't understand this statement sorry.
If you can see light. You have a measurable amount in Lux or foot candles. If you set a per meter next to it would that not create a conversion number?

 

[saltyfilmfolks]

I dunno. I think LUX falls between "better than nothing" and "good enough." It's definitely a step above eyeballing it, but it's still deficient on many levels. My fear is that people might look at LUX levels and think that's an accurate way to determine a coral's needs when it really doesn't tell us much about what the coral actually needs.

Agreed. I think that's also where PUR comes in too.

I'll go back to a per meter was not made for us. You can have great par in your orchid garden. Not goona work that great for a deep water coral.
You have to look at the spectrum amounts provided by the fixture as well. Not just amounts on the par meter as they too can be deceiving

That's why my claim is if you have a good marine coral fixture with good spectrum you can then just measure its intensity and get pretty darned close.
If it were plants I'd say the same but it would be a different fixture w different spectrum. Yellow and red give you great par.

So yea you need to understand all three. What kind of PAR does your coral want in what intensity


Hey thanks for a great thread and debate. I hope to learn a lot.

 

[gus6464]

I don't understand this statement sorry.
If you can see light. You have a measurable amount in Lux or foot candles. If you set a per meter next to it would that not create a conversion number?

Have you ever seen a 400nm LED? To the eye it puts out almost no visible light. A lux meter will read almost 0. If I need to have a par meter next to your lux meter so you can do the lux conversion factor why do you need the lux meter in the first place?

You can't just say "ohh you need to have a lux reading in the whatever range" without knowing the wavelength and source of light being measured. A light with all 400-500nm leds and a tiny hint of lime or mint will look whiter to a person and still read super low lux when the PAR will be sky high.