PAR meter light readings

Tom Barr

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Well, I finally brought a light meter for personal use that measures both sunlight and electronic sources over the 400-700nm useable plant light range.

I measured my EI test tank set up and was surprised to find that the level was fairly close to the max 600 micromoles/m^2/sec that aquatic subsmersed plants saturate photosynthesis at. The amount was 450 micromoles/m^2/sec over the entire central region at 8cm distance from the light source.

Pretty good and pretty high.
I've never known the actual value till today.

Next I'll add a chamber for the water proof design. This will find the PAR extinction for the water proof lens and then be submerged and subtract the lens' removal in the waterproof housing.

This will allow the meter to measure anywhere in the tank.
Very easy to use also.

My first victim, Alan's open house in Napa this Sunday.
Muuuuhahahahaha!!!

I also have a K+ meter that reads to about 0.5ppm of K+ over a 0-50ppm range, far more accurate than any cheesy turbidity test kit. The test are about 1 dollar a pop though.

Regards,
Tom Barr
 

Bonsai_Swamp

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Re: PAR meter light readings

Hi Tom.

What type of light meter did you get? I've been thinking about getting one as well - I'm curious about accumulated light exposure and marine spring plankton blooms.
 

Tom Barr

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Re: PAR meter light readings

Li-COR is one, the other is Apogee.

Regards,
Tom Barr
 

rusticitas

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Waterproof housing

Tom,

I am curious to get get myself the Apogee meter that you have, and was wondering if you ever constructed the underwater housing. Would be interested in knowing what you came up with.

-Jason
 

Tom Barr

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It should be fine as is.

If you cover anything, it'll affect the readings.............

I generally do not risk it and take readings right at the water's surface, or when water levels are low during a water change but many reef folks have used it underwater.

Regards,
Tom Barr
 

rusticitas

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Ah, I misunderstood then. I was under the impression one would take the readings at the surface, and also underwater, perhaps at a midway point, or at the substrate level.
 

Tom Barr

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You can do that. See thr Reef Central review.

Regards,
Tom Barr
 

defdac

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What is the exact lighting setup (type of bulbs and reflectors and tank dimensions (width, height, depth)) for the 450 micromoles/m^2/sec reading?

The reason I ask is that I want to check a calculator I've made and see how close it comes...
 

Tom Barr

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Bulbs are about 1 year old, 55w 8800K and a 5000K, Hamilton ballast, mirrored reflector, at 4" distance (water's surface).

Regards,
Tom Barr
 

defdac

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Hmm.. A really good 55 watt bulb will omnidirectional emit around 40 uE/s of usable plant light. With near perfect reflectors you probably are able to concentrate that light to a say 0.6 by 0.4 metres rectangle giving around 130 uE/s/m^2.
With 4 of those pointing at the same square you reach around 450-500.
 

rusticitas

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Misunderstanding PAR meters

I am realizing that I do not understand PAR meters as well as I thought! As I come from a photographic background, I was likening it to a photo meter. (Obviously, I was not assuming it was exactly the same, just likening it to one.)

In what ways can I use a PAR meter to help me better learn and understand the keeping of plants? It would seem that I could use it for both aquarium plants, and vivarium plants. It seems to me that I could also use a PAR meter to evaluate different types of lighting sources (CF, T5, T8, MH), and perhaps if/how color temperature (ex 5500K, 10000K) can/might affect growth.

Would one want to correlate the electric light to sunlight at any point?

And perhaps I am trying to bite off a lot more than I can chew!
 

defdac

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This is a good article that explains and shows how to use the bulb data from manufacterers to calculate the total PAR/PUR (instead of using a meter):
Aqua Botanic-light bulb comparison

It's over most folks heads though, especially when it comes to making your own calculations.. Have no fear though - I'm making a web 2.0 calculator that is able to both calculate the pur-efficiency of any bulb and also calculate an aproximate light level at arbitrary depths..