Question about lighting - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 3 Old 11-19-2010, 02:08 PM Thread Starter
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Question about lighting

Last night while I was doing a water change I decided to transplant the Amazon Sword that wasn't growing to my 45 gallon tank, and also snipped about 4 inches off of two Wisteria plants that were out growing my 10 gallon and put them in the 45 gallon. I have no idea what watt or kelvin rating the light in the 45 gallon hood has. It came with the tank which was given to me by a friend of the family's.

When I was looking at lights a few weeks ago at a pet store I noticed that all of the watts for the 24" bulbs were the same, 15, but the Kelvin ratings were vastly different. I have no idea what Kelvin rating I'm going to need for this tank. It's a 45 gallon tall, about 36 inches long and 22 inches tall. I plant on having more plants in this tank soon. More Amazon Sword, once they outgrow my 10 gallon completely, more Wisteria, most likely some Pennywort, and others that I haven't decided on yet. Any help in this area would be greatly appreciated. I haven't been keeping plants long and am still pretty ignorant when it comes to the lighting.
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post #2 of 3 Old 01-19-2011, 11:32 AM
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i would say a t8 bulb kelvin ( 6500k to 7000k) a brand name like ge etc..

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post #3 of 3 Old 01-19-2011, 07:19 PM
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Kelvin is the measurement unit for the colour temperature of light [nothing to do with "hot/cold" type temperature]. Light is comprised of various colours, each with its specific wavelength. When you see the "rainbow" you are seeing white light separated into its various colours caused by sunlight refracted through water droplets. Same as a prism.

Sunlight at mid-day is approximately 5600K. A lower K number means more orange/red ("warmer" light) and a higher K means more blue/purple ("cooler" white), in very general terms. Aquatic plants grow best in light between 6000K and 7000K, so one of the "daylight" type tubes having a kelvin of 6500K is perfect. The red and blue is there (aquatic plants need red and blue to photosynthesize) with a balance of green for a natural rendition of fish and plant colours.

"Watts" is the measurement of energy used by the tube or bulb to produce the light. It also has nothing to do with intensity of the light, although in very general terms the higher the wattage the more light is being produced. But with todays better-made T8 (and now T5) tubes and Compact fluorescent bulbs, the energy used (watts) is far less to produce fairly intense light compared to older tubes and incandescent bulbs. They also produce less heat, which is because the energy is not being used so much for heat with the newer types.

Fluorescent tubes are generally the same wattage for the length of tube, e.g., a 48-inch tube is 40 watts. However, the way the tube is made can have a significant difference in the light intensity emitted, and can also use less energy to do so, so the watts can decrease. Some manufacturers make 32w tubes that are equal in light intensity to 40w tubes, other factors (such as Kelvin and lumens) being the same. So when buying fluorescent tubes for a planted aquarium, within the length that will fit your fixture you want to look at the kelvin primarily. Lumens I tend to ignore as most of the daylight 6500K tubes are comparable, at least in my experience. The so-called "aquarium" and "flora" types are not, however, they are usually about 1/2 or less the intensity of daylight or full spectrum.

So, jbonez was correct, a tube with 6500K rating in a "daylight" such as those made by GE, Phillips or Sylvania will work fine; I hope my explanation above helps you to understand why.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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