PAR vs. Lux/Lumens

[davelin315]

I was at a science teacher conference this past weekend and received some light/temperature probes on an educational loan. I am going to use them at first to test out the effects of lighting on temperature and also to see how much light actually makes it through the water, but I'm not sure how PAR and lux/lumens come into play. Anyone out there know how to actually use the lux/lumens information I get from these probes to determine light quality vs. depth of water?

 

The probes themselves are called HOBOs and are completely submersible, very small, and can withstand freezing and boiling, so they'll do great in a reef tank, but I'm not sure what to make of the readings. Any information or references to good information on lux/lumens would be extremely helpful. The probes themselves are made by a company called I-science.

[dhoch]

PAR = photosyntheic Active Radiation... That's to the best of our knowledge the light that plants (and corals) use for photsynethesis...

 

A PAR Meter measures this type of light.

 

LUX is a measurement of visible light (to the human eye).

 

Hope that helps.

 

Dave

[davelin315]

It does help, but is there a correlation between the amount of visible light that is able to penetrate water and the amount of PAR that is able to? Basically, is there a way to estimate PAR based on a lux or lumens reading? I know that there has to be some correlation as visible and ultraviolet light energy are both effected by traveling through water, but I don't know if they are effected at the same rate.

[dhoch]

From my understanding of physicis it should be the same (photosynthetic vs lumes)... there is not enough difference in the wave lengths of the light to really matter in the scale you will be talking about.

 

Dave

[Lee Stearns]

Dave,

My son is setting up a nano cube for his Biology project at Lake Braddock High School and is going to measure as best as possible the effects of lighting and photosenthesis on the chemical composition of the salt water on a mixed reef environment. To keep it simple it will be no skimmer- I would like to get any information of where to get these Hobo's or even just borrow one for a couple of readings. Let me know when would be a good time to contact you.

Regards,

Lee

[ErikS]

Absolutely no correlation between lumens & PAR - can have high lumens & low PAR, also the reverse. PAR deals with a very narrow band of the spectrum, lumens could be any visible light.

 

If there was any correlation I assume Sanjay or others would use the more familiar scale (lumens) to publish data - they don't.

[dhoch]

Erik,

 

But I belive in terms of penetration through water they are equivalent...

 

Albeit you are correct that you can have high Lumens/LUX and low PAR and vice-versa.

 

if one was only interested in measureing light penetration through different media then it wouldn't matter if you were meausring lumens or PAR.

 

Dave

[ErikS]

Yep, that's true - the only "gotcha" would be that different spectrums penetrate further. But then the light we want does & that would mean we were measuring the penetration of the desired spectrum...........seems good.

[davelin315]

Lee - send me an e-mail at school, I have the link and information there. david.lin@fcps.edu Your son should be able to get one himself for loan and possibly win it if he submits his plans.

 

Erik and Dave - does that mean that the measurement of lux would reflect the amount of PAR as well depending on the quality of the light bulb? For instance, if there was a PAR reading done on this particular bulb (Ushio 10K 150W mogul base) then I could extrapolate what PAR would be at the position of the lux meter based on the lux reading as compared to the lux reading at the light itself? I'm having a bit of a difficult time following the debate here...

[dhoch]

Your a teacher...

 

The intensity of any wavelength of light at any depth is described by the following equation Iz = Io e^(-kz)

 

Where

Iz = intensity of light at depth z

Io = Initial intensity of light

k = coefficient of attenuation (more on that in a bit)

z = depth

 

the coefficient of attenuation is the measure of penetration of light and it depends on 2 factors:

 

1) the clarity of the water

2) the wave length of the light

 

So to answer your question... If you can find the dependancy of the coefficient of attenuation on wavelength... (and it's not simple I'm sure).

 

Dave