Lighting in a Planted Tank

This post was originally posted on FTTV by Benjamin Peterson. it's a huge help in trying to figure out what lighting area you may be in. This is a link to a video which explains the chart and how to read it made by me (Shane) - http://www.youtube.com/watch?v=hAT1e6bsOrY - From here forward is a direct copy and paste of his post.

This was posted on Monterfishkeepers.com by jcardona1.

Ok, so we all know the watts per gallon (wpg) rule is pretty much useless these days with all the different types of lighting. there are other ways using lumen calculation but i still dont like this, and is usually pretty damn confusing.

a member on plantedtank.net put together a great chart, using real data gathered with different bulbs and a PAR meter. this is awesome, and is a great reference for seeing what catergory of light youre in when it comes to plants. or how many bulbs you'll need to be in a certain category.

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example, let's assume that i have a standard 55g tank(48x15x18). now, with a height of 18", let's say our light fixture will be 18" away from the bottom of the tank after taking into account your substrate depth of approx 2".

so based on this chart, if i were to run one T5HO bulb (assuming the bulb spans the length of the tank), this bulb would give me 65 micromols of PAR, which puts me in the MEDIUM light category. now if my fixture had two T5HO bulbs, just multiply the figure by 2, which gives us 130 micromols of PAR and well exceeds what is considered HIGH light. this may be too much lighting and could potentially give you algae problems. easy enought right??? Big Grin

same scenario, but let's assume we're using a standard T12 bulb. that gives us 10 micromols of PAR per bulb, which isnt even considered low light. we'd need 3-4 bulbs to be in the low light category. wanna be "high" light with T12 bulbs? gonna need at least 8 friggin bulbs!!!

now you see why T5HO are the most effecient and economical choice when it comes to lighting, especially for planted tanks.

so what do you guys think? can we put an end to all those wpg rules? i think this is easy enough, and should be a good guide for those wondering about lighting. afterall, the hardcore planted tank freaks ignored the wpg rule a long time ago!!! Smile

here's the original quote, and full thread:

http://www.plantedtank.net/forums/li...t5-t12-pc.html

Quote:

I have been wondering how much PAR a typical T12 light produces. Like most everyone else I have just assumed that watts per gallon was a way to guess the light from T12 bulbs, but there is no more reason to expect that to mean anything than there is to expect it to mean anything for other bulb types. So, I decided to do some testing.

I borrowed a new two bulb 48 inch T12 light fixture from one of our local aquatic plant club members, bought a new T12 bulb - a Phillips "Natural Sunshine", 40 watt 5000K, 92 CRI bulb at HD, borrowed our club PAR meter and took some readings. Since I have previously found that I get virtually the same readings with water in the tank and with air in the tank, I omitted the water this time. Then I plotted my smoothed data on a common plot with T5 and PC data:

To compare this with "watts per gallon", I know that a couple of 2 bulb T12 fixtures will grow plants in a 55 gallon tank. That tank is 20 inches deep, so if the substrate thickness is about the same as the height of the bulbs above the top of the tank, each bulb should give about 9 micromols of PAR, or 36 micromols for 4 bulbs. That is right in the middle of the low light range. So my data is consistent with real life results.

The light fixture I borrowed has an acrylic splash shield and a removable back, which is a white reflector. I tested the light with and without the splash shield to find that the shield reduces the intensity about 7%. Testing with and without the white "reflector" shows that the reflector increases the intensity by about 36%. The data used for the chart is with both the shield and the reflector.

Some popular tanks are only 12 inches high. For those tanks T12 bulbs should give about 25 micromols per bulb, so a 2 bulb fixture will give low medium light intensity, probably a good choice for many people with one of those tanks.

I believe T8 bulbs produce about the same amount of light as T12 bulbs, but at a lower wattage, because they are more efficient. The fixture I borrowed uses starters and magnetic ballasts, so I didn't try it with a T8 bulb.

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Permalink Reply by frroK on August 8, 2011 at 11:22pm

got it! thanks dude.. its a power compact... i guess i just looked really quick ..lol

http://www.adana-usa.com/index.php?main_page=product_info&produ...

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Permalink Reply by 2apes2gp667wr on August 9, 2011 at 12:31am

There is no real standard of measuring PAR so the only way to really find out what you have for your tank is to get a PAR meter and measure bottom, middle and top ot the tank. There is no mega high light though. Plants have a maximum amount of light that they will use. Say you put a metal halide over your tank and it gave you a PAR level that was at maximum for the plants you had. It wouldn't matter if you put 100 more halides over the tank, the plant could not use any more than its maximum PAR. Kind of like if you fill a glass with sand. Once its full, no matter how much more sand you pour onto the glass no more sand will get in.

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Permalink Reply by 2apes2gp667wr on August 9, 2011 at 10:25am

Exactly right on the light levels. High PAR at the substrate is even higher at the surface. It's just that anything over a plants highest light requirement is wasted so you can't ever "overlight" a plant, but you will get algae. That's why you want to balance it out. You would use high light because some plants need that to thrive. It's just nature. Some plants need more sun than others.

When I say there is no standard I just mean that the chart is an estimate and the only true way to know is with a meter. You are absolutely right it's a good starting point, but every tank is different. The same light on two different tanks will give different readings because of tannins, shade of leaves, floating plants, etc. Even at the same depth, readings will vary between different areas of the same tank. That is why PAR readings are the most acurrate when done out of the water. But the chart is a good starting point. I would love to find a place that rents a PAR meter to see if the chart is right on. I'm sure some aquatic plant clubs rent them or loan them to members. There's a Boston Aquarium Society I think I'm gonna check out. Should be something like that in every city.

Personally I think a PAR meter for a planted tank is overkill and the chart is fine to use. I'd only get one if I had a reef tank with expensive coral. Then I'd want to know for sure.

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Permalink Reply by Pedro Pedro on August 9, 2011 at 12:05pm

To counteract the algae its good to plant more plants then right?

Does running the lights less time every day also reduce algae?

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Permalink Reply by 2apes2gp667wr on August 9, 2011 at 1:53pm

Yes both will reduce algae. More plants should outcompete the algae for the nutrients it needs to grow and less light will reduce algae growth.

Permalink Reply by 2apes2gp667wr on August 9, 2011 at 3:54pm

It's determined by the plants genes not outside factors.

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Permalink Reply by 1gh7ijdl92ra7 on August 18, 2011 at 7:16pm

thanks for posting this, helps me help others :)

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Permalink Reply by Anthony F on August 27, 2011 at 5:16am

If you have low light bulbs ( I am running 1 T8 8000K in a 20 gallon high [12 inches high bulbs]), do this mean I can run the light for twice as long to achieve the same amount of PAR of two bulbs in half the time? Or does light work differently?

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Permalink Reply by 2apes2gp667wr on August 27, 2011 at 9:07am

Short answer, no, it doesn't work that way.

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Permalink Reply by abraham avelar on October 27, 2011 at 3:23pm

cool thx u made it alot clearer for me

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Permalink Reply by sheathed011790 on December 27, 2011 at 12:10pm

is this also applicable to slim t5 bulbs or to t4 bulbs?

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Permalink Reply by Kevin Nguyen on January 1, 2012 at 1:50am

i have 2 10watt 5100k compact florescent ttwist in bulbs above about 10inches idk if this is even to be considered. i need help with reading this chart