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Lighting Question: What is Kelvin Rating

So your thinking about upgrading from your fish bowl, and are looking at your options for your next aquarium. You start looking at the live plant aquariums or the saltwater reef aquariums and what the requirements are. Quickly you realize that there is a wide range of specialty lighting available, and you have no idea what you are looking at. This is a common problem faced by many aquarium hobbyist.

One of the questions about specialty lighting that I am most often asked from customers in our store is what spectrum, or type, of light do I need for my aquarium. To really understand the answer to this question, you need to understand the universal rating system that is used to describe the spectral out of aquarium light bulbs; The Kelvin Scale.

For those of you who paid attention in science class, you know that Kelvin is a temperature scale in which zero occurs at absolute zero and each degree equals one kelvin. Water freezes at 273.15 K and boils at 373.15 K. Just thought I would throw that in there to confuse you, obviously that does not help describe the spectrum of a light bulb.

Kelvin Rating, or simply K. Without getting too technical, is a numeric scale that describes the color of an object at a given temperature. For aquarium lighting purposes Kelvin rating describes the color, or spectrum, of sunlight in a given environment. Most aquarium light bulbs will have a Kelvin rating between 5000K-20,000K. For example, the approximate Rating of natural sunlight at sea level is 5500K, this is a very warm white light that includes all the colors of visible light(red,orange,yellow,green,indigo,violet) This is the ideal spectrum of light for shallow water aquarium plants and fish. The deeper you go into the water column the higher the Kelvin Rating becomes. 20,000K light bulbs are designed to mimic deep water environments. Red, yellow, and orange light are short wavelengths and get filtered out of the water column very quickly. Blue and green light can pentrate much deeper. The result is that the deeper you get in the ocean the more blue the environment becomes. Animals that live in these deeper water environments have adapted to the light spectrum at these depths.

Now all you have to decide on is what you want to put in your aquarium, sorry I can not help you with that one. Here is a general guide for deciding what Kelvin rating bulb you should choose for your aquarium.

Daylight spectrum (5000K-10000k) bulbs are ideal for freshwater aquariums with live plants and Saltwater fish aquariums, higher Kelvin bulbs (6700K-20000K) are ideal for saltwater reef aquariums.

Hopefully that has shed some light(pun intended)on the different aquarium light bulbs available.

Until next blog,


Species Profile: Giant Clams

Just got back from MACNA XIX in Pittsburgh, and I would like to congratulate the Pittsburgh Marine Aquarium Society for hosting and outstanding conference.
The next few Blog topics will be about some of the Seminars and Events that I attended at this years MACNA conference.

One of the seminars that I found really interesting was the Giant Clam presentation by James Fatherree. James is the author of the book “Giant Clams in The Sea And The Aquarium”and gave a presentation based upon some of the most common questions that he is asked about Giant Clams, and the Answers to those questions.

How much light do I need to keep a Tridacna Clam? This is a question that I am commonly asked about clams from our customers here at TFP, and one of the questions that James Fatherree addressed during his presentation. How much light is needed is probably the most important question to be answered, in regard to keeping giant clams in the aquarium. Giant clams receive as much as 100 percent of their nutrition from light that provides energy for photosynthesis for their symbiotic algae (zooxanthellae). How much light depends much upon the species of clam that you are trying to keep. Clams are found in the oceans throughout a wide range of depths in the tropical Pacific Ocean, from near the oceans surface, down to more than 25 meters (83 feet). Some species are only found in fairly shallow water, like the Tridacna crocea, which require very intense lighting. Others Giant Clam species such as T. maximaand T. squamosa, are found at depths of up to 15 meters (50 feet) and required strong lighting. Another species of Giant Clam that is commonly kept in the aquarium trade, T. derasa, is found at depths of up to 25 meters (83 feet) and require moderate lighting. All these depths are extreme maximums, under ideal conditions. The vast majority of clams found in the wild are found at much shallower depths than these maximum. All species of Clams that are grown in commercial farms are typically grown in shallow pools or raceways under intense lighting.

The best answer to this question is that there is no such thing as too much light for Clams in the aquarium. Deeper water species, like Tridacna derasa and Hippopus hippopus, will tolerate fluorescent lighting in very shallow aquariums, or high output T-5, VHO, or Compact Fluorescent lighting in aquariums up to about 24” deep. All other clams should only be kept under the intensity of Metal Halide lighting. The deeper the aquarium the higher wattage metal halide light should be used, in general the more light you can provide, the higher your chances for long term health and growth.

For more great information on Giant Clams check out James Fatherree’s book “Giant Clams in The Sea And The Aquarium”

Hope this sheds some light on questions that you may have had about clams, until next time.