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Whether you have a planted tank or not, some kind of lighting is required for the freshwater aquarium. Fish need light to see. It is also important in the reproductive cycle. The amount (intensity) of light for a fish only freshwater aquarium is a bit difficult to answer. It is usually recommended that lighting be kept on 10 to 12 hours per day. This may need to be varied due to algae growth, personal schedules etc.
What is light? Simply put,; light is energy that travels in waves. These wavelengths come in many sizes. The light wavelength we can see is 400 to 700 billionths of a meter (Pretty small huh?). Light also has frequency which is the number of waves passing a stationary point at any given time frame (usually one second). Enough, Enough of the techie stuff you say!! Well almost. The frequency of visible light is known as color. (Ah Ha back to something we know about). Red, a warmer color, is 430 billion Hertz (Cycles per second) while violet, a cooler color is about 730 billion Hertz (Pretty fast huh and no they don't rent cars).
White light is a mixture of all of the colors of the visible spectrum. If you have ever seen a rainbow, it is really white light broken down into its component elements. Why are you telling me all of this? Well we now know that different colors are basically energy traveling at different speeds and wavelengths. As light travels it is absorbed, reflected and scattered. Plants absorb light in their growth cycle. This is called photosynthesis.
A pigment is any substance that absorbs light. Chlorophyll is the green pigment used in plants for photosynthesis. The green pigment absorbs reddish orange and blue light from the visible color spectrum. In the planted tank, this is the color spectrum we need to promote plant growth.
Another thing, almost all non-blue light is absorbed as it travels through the atmosphere and water. In water it is absorbed at much greater levels. Wow, now we know why things look so bluish under water (clean water that is). in fact, below 3 foot, it is almost all blue.
Bear with me one more second; we need to clarify two more terms.
Light color is measured in degrees Kelvin. The warmer looking bulbs (more red and yellow) are lower on the Kelvin scale which is measured in degrees. The cooler the bulb (more bluish and violet) are higher on the Kelvin scale.
CRI (Color Rendering Index)is how a bulb shows the true color of the object it is reflecting. In other words, 100 CRI would reflect the true colors of an object while a low CRI would make objects appear a different shade or color.
Ok,Ok, enough, What about my aquarium?
I'm glad you asked that. For a fish only tank,light as we mentioned earlier is still needed. Fish can see and need light to see. Remember, light is also energy. The light color is not so important, although recent studies show that some fish prefer certain color lighting and certain color lighting can induce spawning. This makes sense since they can be found at different depths in their natural habitat. As mentioned earlier, light is important in the reproductive cycle. For the fish only tank, you should have about 10 to 12 hours of light per day. The type of lighting and it's color can vary, and will affect how your fish look. You may need to vary the intensity and hours depending algae growth.
For a planted tank, we can determine how much light is required, depending on the type of plants that are being grown. A rough rule of thumb is 2 watts per gallon for plants with low light requirement, three to four for plants of medium light requirements and 5 watts per gallon for plants that require heavy lighting.
This assumes you are providing the right color range for photosynthesis to work (Remember, the reds and the blues in the color spectrum). Again, 10 to 12 hours per day.
I am going to leave the Power Compact and Metal Halide lighting discussion for another paper. Suffice to say that this type of lighting is usually left for heavily planted tanks and reef tanks. They are high cost lighting systems but very efficient and excellent for those applications. Planted tanks can also use regular fluorescent lighting as we will see:
This is your standard light bulb. It's main advantage is that it is not expensive. Many of the prepackaged kits sold in fish supply stores use this type of lighting. Its major disadvantage is the heat that it generates. On smaller tanks, especially during the summer, this heat can severely affect the aquarium's water temperature. Wide swings in the aquarium's water temperature can lead to increased stress and Ick. You also want to be careful in removing the hood on an aquarium with this type of lighting. It can get pretty hot!! Any water on a hot incandescent bulb can shatter it.
Incandescent bulbs are around 2700 degrees K (degrees Kelvin) and have very high CRI ratings (95 to 100). Now you know why I explained it earlier1) Their output is in the reddish or warm part of the spectrum. Little to no blue output, consequently making them almost useless for photosynthesis. Their Lifespan of about 1000 hours.
In my opinion a much better choice for the aquarium. They are 2 to 4 times as efficient as incandescent. Run a lot cooler and last a lot longer. You can get different affects with different bulbs because they come in a variety of colors. While the fluorescent bulb lasts longer, they need to be replaced about every six months on the planted tank because of cathode decay, reducing its intensity. Types of fluorescent bulbs
They also come in many color ranges:
Cool White and Warm White
These are the most commonly used and the least expensive. Ok for fish only tanks. Remember, plants require red and blue. These peak in the green spectrum.
Daylight
Closer to a natural color and would be better for plants and still inexpensive.
Plant Grow
Plant grow bulbs peak in the red and blue spectra. They look kind of purplish in color when they are turned on. Wide or Full spectrum plants bulbs are also available at a bit more price. They look pinkish. Full spectrum bulbs try to imitate sunlight around 5000K color range.
Plant grow bulbs are more expensive (10 to 20 dollars in the fish store) but deals can be found at other stores like gardening and home improvement stores. Now that you know what you to looking for (5000 to 5500 K for plants).
When you are purchasing your next tank, or looking at changing an existing one, consider the lighting requirements. You are your fish will be happier for it.