# How do I determine how far a light will penetrate?



## CatG

Hello,
I was wondering how I could tell how far a particular light will penetrate through water and still be able to get the proper color spectrum to the depth I need. I have a 150 gal tall tank that is about 31" from top to bottom, and I need to know what "specs" to look for in a light that would show me how far the light will penetrate. I have done some reading about lights and par/pur values, lux, lumens, etc and find it all very confusing. I am afraid I don't understand much, if any, of it.

Any help would be appreciated.
Thanks,
Cat

Ps. If it makes a difference, I am looking into LED lights for this purpose.


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## Seattle_Aquarist

Hi Cat,

Our club has an Apogee PAR meter and that is the way I determine the light penetration in my tanks. You are correct in that a 31" deep tank will provide challenges. I have a 24" deep tank and it is difficult enough. Here is a good link on lighting intensity verses bulb type and depth of tank.

When doing my research I found that the reflector has as a great deal of impact on the ability to get light to the bottom of my tank. That is why I went with the AH Supply CFL kits with their MIRO4 reflectors. With my 1X96 watt kit I can achieve a reading of about 106 'Micromol' at a 21" depth.

The LED fixtures I have seen and tested to date seem to have trouble attaining this level of illumination. If you like the "look" the LED fixtures give an aquarium with the shimmering surface why not use T5HO or CFL as the "workhorse" portion of you lighting and an LED strip light for the special shimmering effect?

Here is my 45 gallon (tall) 24" deep tank


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## bamboosharkbark

a reminder, if you go with leds get some lenses witht hem as this hugely increases the amount of light that penetrates to the bottom get ur hands on a par meter if you want to check


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## CatG

Thanks for the replies!

I want to do LEDs if possible due to the relatively higher costs associated with the other lighting options. It seems to me that flourescent lights are going to cost me a good deal more in the long run with bulb replacement and energy usage. Plus, LEDs take up less space and seem to have a cleaner look.

However, I do not know if the LEDs can penetrate that much water and a glass top, and still have a useful spectrum at depth. Is there a rating to look for in an LED that might give me this info? I am unsure what a micromol is or what it means. Is this the rating I need to look for? I could buy a meter to check, but they are expensive, plus I would have to spend money on a light fixture to be able to test it, and then have to pay shipping to send it back if it didn't work out. I really don't have the money to do all of that, although I would LOVE to have one of those meters to play with.

I have seen LED lenses mentioned, and I wonder if this would do the same thing: http://telesightmagnifiers.com/catalog/i144.html

The LED fixture I was thinking of is one mentioned on this forum by another poster. It's this one: http://www.ebay.com/itm/White-Hydro...n_0&hash=item2eb16891f1#ht_8869wt_946&afsrc=1

Do you think this magnifier would get that LED light to the bottom of the tank and still have a useful spectrum?

Thanks again!
Cat


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## bamboosharkbark

the website I linked has the lenses you would require. Theres a few option 120degree, 60degree, and 45degree. With some of the narraower option you should get enough light reaching the bottom. Ive seen huge reef tanks that use leds and can grow corals which require more light than planted tanks.

here are some useful links:

http://www.plantedtank.net/forums/lighting/153331-diy-led-lighting-project-suggestions-please.html

http://www.plantedtank.net/forums/lighting/155364-leds-so-many-choices-make.html


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## bamboosharkbark

Oh and I personally would stay far away from the ebay grow lights. they use 1 w leds I think and would not have the versatility of lenses and you would be unable to change anything on it if failed. THey also would not grow plants in your tanks because of too low output and penetration. DIY leds seems difficult but learn how to do it and you'll save money and be in control of everything.


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## CatG

Thanks so much for your input.

So, just so I understand, you are saying that the 711 light LED panel won't work for that depth, even with that magnifying sheet? If so, that is too bad, because it seemed to be a really cost effective solution.

I emailed the guys at Cree and they told me I would need about 48 LEDs for that tank using 80 degree lenses to get a good spread, but they weren't real specific as to whether the correct spectrum would make it down to the bottom. All they said was that the red and blue would make it down that far, but would not be very intense. (this was taking the lenses into account) I am not sure what "would not be very intense" means. They also suggested I put some red LEDs in the mix, using 40 degree lenses on those to focus it down, but he said it would definitely look red, which I don't think would look very good.

Cat


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## Zapins

It doesn't matter so much to plants what the exact spectrum of light is that reaches them is. Plants have accessory pigments that convert most wavelengths of visible light into usable energy. In conditions where there are less of one color and more of another the plant simply increases the number of pigments that absorb the abundant light. As long as the intensity is relatively good and the light isn't 100% green light or yellow light the plants should do alright.

As far as aesthetics go, I think the sales man might be right about adding more red bulbs to the tank. Red is filtered out pretty quickly in water so the light that reaches the bottom will be more blue/white looking. Adding more red will increase the amount that reaches the bottom making things look more normal. If you have ever seen a tank with 10,000 k (blue/white) lighting vs. a tank with only 6,500 k (warm/full color), you'll know what I'm talking about.


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