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Old 02-21-2011, 09:49 PM   #1
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Lighting Guide for a Planted Tank

Due to frequent questions on lighting for a planted tank I've decided to make a small reference thread for lighting conditions in a planted tank. Hopefully we'll answer some questions. Anyone with knowledge feel free to contribute. Anecdotal evidence is also welcomed.

The Bulbs:
Planted tanks can be daunting. There are the myriad of species and cultivars that go misidentified or unidentified, countless fertilizers and regimens, frighteningly imposing CO2 setups and what comes up the most is also one of the most important investments in planted tanks: Lighting.

There are 6 basic types of lighting used in a planted tank.

Self ballasted spiral compact fluorescent bulbs (CFL)
Power Compact (PC)
T5 NO fluorescent
T5 HO fluorescent
T8 fluorescent
T12 fluorescent
Metal Halide

The most common fixtures take 15 watt or another relatively low wattage T8 bulbs or have screw in seats that are compatible with CFL bulbs. Often times stock fixtures are underpowered for plant growth. A general rule of thumb -but no longer quite accurate- is the watts per gallon rule. If you have T8 lighting the rule generally is:

less than 1wpg -> unacceptable for plants
1 -2 wpg -> low light to medium low light
2-3 wpg-> medium light to medium high light
3wpg+ -> high light

(Also applies to CFL bulbs)
**T12 bulbs have a wider diameter and wider spread. Their light is therefore more diffuse. The wpg guideline is similarly applicable but you will need slightly more light. Generally, T12 bulbs have come out of use in aquarium applications.

Strip fluorescent bulbs are not self ballasted. A fixture rated for 15watts will only take 15 watt bulbs. Higher wattage bulbs means more bulbs or a new ballast. Basically a new fixture.

Other bulbs such as HQI Metal Halide bulbs and T5 bulbs follow different rules. The theory of the WPG rule rests on the assumption all lights put out the same photosynthetically available radiation (PAR), this of course is not true. PC lights are comparable to T5NO bulbs, while T5HO bulbs are much farther ahead in PAR than the former. HQI MH bulbs are milestones ahead in terms of PAR. Simply put, watts were not all made the same.

More detail can be seen here:PAR vs Distance, T5, T12, PC

Between T8 bulbs and T5NO and PC bulbs there probably isn't enough difference in PAR to modify the WPG rule for them.

T5HO bulbs are another beast all together.

As a rule of thumb:

1wpg T5HO -> low to medium low light (sitting on the top of the tank)
1-2wpg -> medium light (Elevated above the tank)
2-3 wpg -> medium high light to high light (Elevated above the tank)
3+ wpg -> very high light and algae and CO2 fest. (Elevated above the tank)

HQI bulbs are like having the sun on your tank. I have no experiences with them. But, judging by the success of reef keepers and their corals which have much higher PAR requirements than plants, an HQI fixture, provided it has enough spread and is reasonably sized, will always put you in medium to high light.

I don't know enough about LEDs to give an opinion.

Important: WPG doesn't work the same way on really small tanks and really large tanks. The ratio of lumens: sq. in. cause discrepancies in WPG. Generally you want more WPG on a really small tank (1-10 gallons) than would normally be required. While a very large tank will reach high light with less WPG. Considering I have little experience with really large tanks someone else can shine some light on this.

Reflectors are also very important when it comes to lighting for a planted tank. White paint alone can increase the amount of PAR put out by a fixture by as much as 36%. Plain sheet aluminum will see even greater gains. Some very high end T5 and PC fixtures will use MIRO4 polished aluminum to reflect light. The gains made by these reflectors can nearly double your PAR output. If you can't find aluminum or if you're not a big DiY-er a simple coat of matte white paint can make a world of difference.
When looking for a high end fixture, you should find one with individually reflected bulbs or one with a parabolic reflector. It'll make the money you spend worth it.

Important: Glass mirrors are poor reflectors and should not be used. They are more expensive and reflect less than even white paint.

Color Temperature:
Color temperature is a relatively unscientific way to identify what color a light will be to our eyes. It's based on some hoo-ha I don't really know how to explain well. You are looking for a bulb with anywhere from 5000k- 10000k color temperature. The higher the temperature the more blue a light will be. 20,000k bulbs are bluish. 2700K warm lighting bulbs are disgustingly yellow.

Why does color temperature matter? Plants absorb light in the red and blue ends of the spectrum while reflecting green. 5000k - 10000k bulbs tend to have spikes in those particular wavelengths - more PAR.

If you don't like a certain color bulb mix them up to find your own personal favorite. It's your tank. Make it look like what you envision.

Okay, so why does any of this matter? Simply put, lighting will decide what plants you can keep. Some low-medium light plants that are popular in the hobby are:
Echinodorus (sword plants)
Egeria Densa (anacharis)
Guppy grass
Java Moss
Java Fern
Some Rotalas
Water sprite
Various Hygrophilas (water wisteria and brethren)
Marsilea sp (water clover)

High light tanks require CO2 addition or some other carbon source (Excel, or just plain gluteraldehyde for you money savers). Medium light tanks also benefit from CO2 addition. Most planted tanks will benefit from the addition of micronutrients. High light and some medium light tanks require fertilization due to growth demands.

Remember, you don't need a 300 dollar light fixture to have a beautifully planted tank. Just pick your species correctly and you too can grow some gang buster plants.

If I made any mistakes or if you disagree with me, chime in and add your opinions/facts. If you know something that I don't know please contribute.

A lot of this information came from information I've garnered from the folks at Aquatic Plant Central and The Planted Tank. Special thanks to Hoppy of TPT (if you ever see this) for your huge contribution to the hobby.

I am mistaken, you want matte paint. Not glossy paint.

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Old 02-21-2011, 09:50 PM   #2
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This should be stuck!

Great post crepe!

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Old 02-21-2011, 09:58 PM   #3
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Looks good to me. Excellent post. It should be a sticky. Will save lots of typing
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Old 02-21-2011, 10:14 PM   #4
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I agree...thanks for the post crepe.

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Old 02-21-2011, 11:17 PM   #5
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Great post!

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Old 02-22-2011, 06:29 PM   #6
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Cleared up that lil debate we had going on there lol. Great post!

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Old 02-23-2011, 12:16 PM   #7
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Excellent thread. I would also like to see this made a sticky.
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