All About Aquarium Lighting

All About Aquarium Lighting

Written by George J. Reclos Wednesday, 09 January 2002 01:00

PDF | Print | E-mail

Article Index
All About Aquarium Lighting
Page 2: Light Sources
Page 3: Characteristics of Light
Page 4: Glossary
All Pages

 

Lighting is a key issue in fish keeping - I am sure most of you know that. Your particular set up may require too much or too low lighting, special colour lighting (colour temperature), special type of lighting (e.g. need for deep penetration), even lighting at special angles. All those elements can make a tremendous difference in what you and your visitors see when they look at your display aquarium and may also have a great impact on the well being of the animals and plants you keep in there. Of course, all those elements, when not explained in detail, create a much bigger confusion which forces hobbyists to opt for an "average" solution. What's worse, there are no rules of thumb and those that exist should not be used - another reason for more confusion. There are some principles though. Let's start by saying that the lighting requirements are dependent on the animals, plants and invertebrates which live in your tank and not on the size / shape of the tank.

Indeed, there are several issues related to lighting: Type of light source, amount of light (in Lumens or Lux but not Watts), light colour (more correctly: light temperature measured in degrees Kelvin), quality of light (CRI), duration of light and many more. Yes, things are not simple at all, when it comes to lighting. No wonder there is a whole chapter about it in our Physics books. I will try to make this issue as simple as possible but not oversimplify it. The aim of this article is to provide enough information for the hobbyist and enable him to choose the right lighting equipment because he knows what he is looking for. The article will have succeeded its goal if more and more hobbyists visit their pet shops asking for lamps with specific characteristics instead of relying on what is stock (or what the shop works with a greater profit margin). Of course, this is not going to be an "easy reading" article. It couldn't be - and it shouldn't be!

Light colour (temperature of light source). Our eyes (and of course the eyes of our fish and our plants' photosynthesizing elements) are "calibrated" to perform in ambient sunlight. Subsequently, our eyes interpret this light as white light. As all of us know, "white" light simply doesn't exist. In simple words, "white" is not a colour but a combination of many wavelengths (colours), which form a spectrum (see Glossary at the end of this article). What we perceive as "white light" is actually the average of the solar spectrum. This spectrum comprises roughly from six basic colours (and all their hues since the spectrum is continuous): Red, Orange, Yellow, Green, Blue and Violet. Those colours are listed in ascending frequency order (or descending wavelength, thus the Violet has the shortest wavelength and the highest frequency - hence higher energy). The visible wavelengths range from 760 nm (deep red) to 380 nm (violet) - see Diagram 1.

In the left diagram (Diagram 1, above) you can see the full spectrum of the visible light. Visual light is a tiny part of the electromagnetic wave spectrum. The right diagram shows the spectrum of sunlight. As you can see, the spectrum is continuous, while not all colours are emitted with the same intensity. However, all animals living on the surface of the earth or very shallow waters (sea or lakes) have light sensors (eyes or other organs) "calibrated" for this spectrum.

Any wavelength longer than 760 nm is in the infra red (IR) region while anything shorter than 380 nm is in the Ultra Violet region (UV). One very common misunderstanding occurs when we discuss the "temperature" of the light and the "warmth" of it. To the human eye, the "warm""cool" ones are at the bluish end of it. However, when we refer to light sources, things are exactly the opposite. Sunlight white usually has a temperature of 5000-5500 K while light sources rated at higher temperatures contain more and more blue in them (10000 - 20000 K) - see Diagrams 2 and 3 and Table 1.

Diagram 2 shows a full spectrum, low temperature light source. Note that the red / yellow region is enhanced while the emission in the blue region is reduced. This resembles the emission spectrum of an incandescent lamp.

Diagram 3 shows a full spectrum, high temperature light source. The red, green and blue regions resemble that of the sun. Compare this spectrum to the "bands" of the spectrum emitted by the full spectrum aquarium tubes (photos 2 and 3).

Of course, "white" is something relevant. We see the light coming from an incandescent lamp and the light coming from a normal fluorescent tube (the "cool white" ones) and we interpret both of them as "white", especially when we have nothing to compare them against. However, if you take a picture of those two light sources on a regular (daylight) film, you will see that the incandescent lamp is yellow while the fluorescent tube is green - see Diagram 2 and 4.

Diagram 4 shows the cool white fluorescent tubes found in most homes and buildings seem to be white while actually they emit a big amount of green light, which makes them unsuitable for the planted tank. This can be captured on daylight film.

This difference may not be crucial when reading a book, but it is very crucial for the well being of your corals or freshwater plants which need the energy of the red and especially the blue rays. Moreover, it is perfectly possible to create "white" light by mixing the three basic colours (red, green and blue). This creates a white light, although in this case the spectrum is not a continuous one but one which shows three peaks (or bands). This is the case in most good quality lamps. It goes without saying that, depending on the mixture of the colours a different result is obtained. Thus, the cheap household fluorescent tubes create a "green" cast with a narrow spectrum, the "full spectrum" lamps create a bright white colour, while the so called "actinic" lamps have a very narrow band in the blue section of the spectrum.

Some other factors that you should know (and perhaps use them to work for you) is that the shorter wavelengths (greens and blues) are less scattered in the water (and the air) therefore more penetrating while the red, orange and yellow rays are far more scattered (which is the typical answer to the question "why is the sky during the sunset orange?"). So, in an ideal, full spectrum lamp, more green and blue will reach the bottom than reds and yellows. Your plants will definitely appreciate that and the colours of the fish will be enhanced. However, you will "feel" that there is less light in your tank than actually is. In contrast, the red - yellow - green colour creates the impression of more light in your tank.

Moreover, the human eye "receives" different colours in different ways. If you had to take a look at monochromatic light sources (only one colour emitted) of the same intensity, then you would think that yellow is brighter than the rest and blue the dimmest. Keep in mind that the human eye is more sensitive to the green colour (hence the more green emitted by the normal tubes). Apart from that, red creates the "alert" feeling, orange the "warmth" feeling and blue the "cold" one. Thus we have two factors that make visual estimation almost impossible: One thing is what we see and another thing is how much light (and what type of light) reaches our plants, corals or fish.

Light is very important to the well-being of many organisms we keep in our tanks. Thus some of the organisms we use to keep in our tanks depend on light for their feeding needs. Corals, for instance, use the products of photosynthesis (food and oxygen), provided from the symbiotic zooxanthellae that live within their tissues. Zooxanthellae, on the other hand, use the by-products of corals with come in the form of carbon and wastes rich in Nitrogen and Phosphorus as their food source.

Light is also essential for the function of colour pigments of some organisms, while some other organisms use light to manage vitamins and/or minerals, useful for the constructing or maintaining structures of their skeletons.

Another critical fact for the right lighting of an organism is the angle that the specimen is placed in the tank. Some organisms prefer direct light, while some require that the light will "hit" them not directly from above but at an angle. Some others prefer to get the light obscured by shades. As already pointed, the species you will keep will determine the kind of light you need.

 

< Prev		Next >