The CassiDietsch Zoo Fish Page


Here is an excellent page on Tank Lighting one of the most talked about subjects in the plant tank hobby. Did you know that the recommended amount of light for a planted tank is 7000 - 15000 LUX. Oh LUX is Lumens per square meter. Do you know how many Lumens your bulbs put out? Well most of us do not but if you are curious a Link within the tank lighting link above can help, and here is a more detailed link, and one more. But really most of us do not think about it in LUX as much as the old rule 1.5 to 4 watts per gal. And boy, that too is a large range for determining the right amount of light. Which one do you choose? Well it depends on a few things, like what type of plants you have, and this site can help you there(towards the end). Another consideration is this the depth of the tank and as you may have noticed LUX is sq meters and doesn't consider depth. A third thing is the spectrum of the bulb you use, plants want blue and red light the rest is almost extra and algae really do not care. Also how far above the tank are your lights. For standard florescent bulbs you want to get them as close as possible. So the bottom line is there is no one answer to the lighting question as with many of the variables in the hobby. The right amount of light depends on a lot of factors one of which can be how fast do you want your plants to grow. What about Kelvin, and no, not the comic strip character. Kelvin in lighting refers to a perception as to what the light looks like and is also called color temperature. Color temperature is the term referenced as Kelvin and refers to the weight of one particular color in the spectral output of the bulb. So a bulb with a high Kelvin value like 10000K is a very blue light and one with a low rating is more red. Now, so what you say, but the relevance of this term is in that natural sun light at the equator, in tropical regions is approximately 5000K. So since our plants are mostly from the tropical regions we want a bulb that is near 5000K, and also since water absorbs a lot of red light the trend is to pick a higher Kelvin bulb as opposed to leaning to the low end. Now what about CRI, well that is another non-scientific term. It refers to the lights ability to illuminate an object and make it appear the color that natural sun light would make it look. CRI, color rendering index, is a measure of how close this lights looks to natural sunlight. Therefore a CRI of 100 means the light is a good spectrum, almost full. But a low CRI would be offered by a light that was very blue since the object would appear to blue. But keep in mind the numbers do not tell all, take the GE Plant Light Bulb for example. This bulb is excellent for growing plants and the CRI is -2 and the Temp is around 6400K. The same reason this bulb is great for plants is the same reason that the specs appear all messed up. This bulb was developed with a combination of phosphors that will output a very high amount of the red and blue portions of the spectrum with very little in between. This makes things look a purplish pink and therefore mess up the numbers. And another thing that makes this bulb N/G despite the fact that it can grow plants is that it will make the tank look funny. But if you want a black light poster as a back drop, this bulb should make it glow pretty nicely.

Now you are even more confused, and just say so what do I do.

  1. Get lots of light. Rip apart or through away you typical strips and fit a few more tubes on that tank so you have at least 2 watts per gal. I have retrofitted existing strips to hold two tubes and added new ballasts, and I have build full hoods from scratch. Remember a 55 will nicely accommodate two twin tube 4 foot fixtures.
  2. If you are setting up a new tank, get one that is 4 feet long as the 4 foot bulbs are the cheapest.
  3. If you have to skimp on the wattage, make up a good reflector. A good mylar reflector can increase the lux on the tank by 30%.
  4. Get good bulbs. The best are Tritons and Penn-Plax Ultra Trilux. These are aquarium specialty bulbs and thus cost. I am familiar with the GE numbers, but Phillips and Sylvania also make similar tubes. I recommend the GE Chroma 50, GE Daylight and Daylight Deluxe, and GE's newer series the GE SP50, SPX50, SP65, and SPX65. The GE Plant and Aquarium Bulb actually works nicely when mixed with other bulbs to add some blue. I run a mix, the Chroma 50, PL/AQ, and Daylight Deluxe make a good look. Here are a few spectral output curves for a few bulbs I have considered.
  5. Or if you want you can go with the Metal Halide lighting. It is reported to be of the best. I myself like the slim-line look of a tank covered, but the hanging pendants of MH lighting also offer other advantages.

Always remember to replace your tubes on an every 6 month basis. They loose a lot of their intensity by that time and you will start seeing that in, degraded plant growth and possible algae breakouts.

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Jeff Dietsch

Last updated 7/02/02 JCD