Shedding light on Aquarium lighting

The correct use of lighting of your aquarium depends entirely on the specific set up, and influences growth of plants, corals and invertebrates, as well as the behaviour of your fish. Incorrect use will cause many problems and is related to things such as CO2, nutrients and photosynthesis.

There are basically four types of lighting suitable for fish tanks. These are;

Now, from your school days you will probably remember the rainbow colours. "ROYGBIV" as I used to call it; red orange, yellow, green, blue, indigo and violet. The main ones associated with "colour temperatures" - and measured in Kelvin (K) are Red, Yellow, Green and Blue. Red and yellow produce lower temperatures whereas Green and blue produces higher temperature (unusual since one often thinks of red and yellow as being hotter as they are brighter! Indeed blue is often thought of a cold colour). Sunlight is about 5500K.

Now, to confuse matters more there is also the figure of CRI, the Colour Rendering Index. This is on a scale from 0-100 where sunlight is 100. In sunlight we see things as they are supposed to be seen - put on blue tinted glasses and you see things in a different manner. There is also the Lux or Lumen figure, which tells you how intense the colour is. For example something of very low Lux, might have the correct "colours" but might be so feeble that you can’t see anything that it is trying to light up. Indeed any light moved 2" away from an object will be 4 times less intensive.

Lecture over. So here now are some hints on how to use the correct lighting on your tanks, based on observations I have made over the years;

• Light is a catalyst. Too much red light, when combined with high nutrients on the water will stimulate algae. The K value in this case is around 4000K
• Too much light with silicates will result in brown algae.
• Too much light with phosphates will result in more red and greenish algae.
• Dust, humidity and water turbulence affects the amount of light hitting the water.
• Dirty plastic or glass covers will cut down the amount of light hitting the tank.
• Whilst too much light won’t blind or cook your fish it may make them uneasy about swimming near the top of the tank. Don’t forget, fish can’t blink!
• It is good to provide areas in the tank which are sheltered from overhead lighting.

The types of lighting;

Fluorescent Light These are by far the most common type of aquarium illumination. Whilst most of use leave the tubes in situ until they finally pop their clogs, they should ideally be replaced every 6 to 12 months. During their life span they significantly lose their brightness, especially with the build up of calcium and other deposits caused by condensation and spray. The other reason is the phenomenon known as "cathode decay". More on that in the next paragraph! Generally lighting is used in tanks for two reasons; 1) so that we can see the fish and 2) to enable plant growth. Naturally deeper fish will appreciate lower lighting than, say tanks with corals polyps and light intense life forms. Generally provide areas of shade in all tanks. Careful use of the correct "colour intensity" of lights will provide the correct light for those tank inhabitants. Particularly in Eastern countries who produce man-made varieties of fish, they use specific types of lights that ‘show off’ the colours. Be warned that many tropical fish shops try the same selling technique, and you could find that once you have bought the fish and put them in your own tanks, the colours look quite different! Unless you wish to show off a particular type of fish, a full spectrum tube is likely to be the best option. Tubes with blue ands red spikes are the best option for promoting photosynthesis, with red being the best spike for plant growth. But remember that red colour also enhances algae growth in combination with high nutrients. A bit of physics lessons for you; Fluorescent lights work by placing an anode and a cathode at opposite ends of a glass tube. The tube is partially vacuum with a small amount of mercury vapour. When switched on the vapour is ionized and emits ultraviolet radiation. The inside of the tube is coated with a phosphor and it then "fluoresces" (gives off light) when it is stimulated by ultraviolet radiation. This then produces the visible light that makes the tank light up! It is the chemical makeup in the tube which gives it the particular spectrum of colours that we ask for when we select the particular type of tube we want.

Oh yes, and that "cathode decay" I spoke of earlier. That is where the over time less energy is transferred through the mercury vapour. The effect of this is that the tube emits less light as it gets older. And, if you ever wanted to know, 90% of all fish tubes made are 4 foot long! And, as a result, inch for inch this is the most financially economical size to buy!

Type of tubes available tend to be daylight / plant growth / full spectrum / Tri-phosphor (these ones emphasise the primary light colours red, green and blue, and tend not to emit ultraviolet. Therefore these are often the tubes used in clothes shops as they don’t bleach the garments!) / Actinic (emit from only the blue end of the spectrum and therefore are best used in marine set ups needed for the marine algae, anemones and corals. Also blue is a good colour if you wish to see your "night fish" such as catfish scurrying around the tank because they think it’s night time. Catfish also cannot see red light, so a red light in the tank will enable you to watch them in the dark without them noticing you. However, the chance is that if they can’t see you, they probably won’t see other fish scavenging around for a nice catfish meal!

Halide Lighting These are a more expensive form of tank illumination and this type of light produces by far the most intense lights with a lower angle of illumination. This type of lighting is therefore best for plant growth and invertebrates. As a general rule-of-thumb, think of using the ratio of 3 to 5 Watts per Gallon of water. Therefore a 50 Gallon tank would require around 200Watts. Also bear in mind the amount it will cost you in juice to light a tank this way! Also bear in mind that the fish in your tank probably don’t want this kind of intense lighting; watch the behaviour closely and provide areas of shade for them! A halogen bulb has a colour temperature of around 3000K and usually lasts for around 2000 hours.

Incandescent Lighting means using a normal Edison light bulb, just as you use to light up your house. This method is certainly less intense than halogen, but this type of bulb provides (as in the halogen bulb) lots of heat! So use it wisely! Bulb and halogen bulb lighting is best used as a supplement to a fluorescent tube for promoting plant growth due to the extra heat produced. Note also that it has a high CRI of near to 100 and has a heavy red content. The Colour temperature is around 2700K. A typical bulb lasts around 1000 hours, though the Guiness Book of World Records has listed one that lasted for over 70 years! The main reason for this is probably because being in a fire house in Boston it has never ever been switched off. Shoving high current on and off a filament does it a lot of harm, and this is illustrated by the fact that usually a light fails to work at the point when it is being switched on.