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Home > Articles > Questions on Lighting

Tuesday, 22 November 2011

Questions on Lighting


How long should I have the light on a fish only tank?
I recommend 8-10 hours a day maximum, though it is not very important to have your lights on.

What lights do I need for a fish only tank?
In a saltwater fish only tank the light is not important.

How long should I have the light on in a reef tank?
• If all is fine in the aquarium allow the light to be on for 10-12 hours.
• I recommend if you have any trouble with algae have your lights on for less time, 8-10 hours a day.
• It is better if the lights are on timers to achieve consistency. Try to set them so the tank is illuminated around the times it is most likely to be viewed.
• Some people like to set the actinic lights so they come on before and go off after the full spectrum lights. This limits stress on the organisms and imitates the sun rising and setting, plus it allows more time for the corals to obtain energy but not the algae.
• The tank must have no light at night (there are moon tubes that imitate the moons light, these can be use to achieve mass spawning).
• It is not really true that weaker lights should be kept on for longer periods of time to achieve more of an effect due to increased photosynthetic time.

What lights do I need for a reef tank?
• The lights you get will govern what you will have success keeping. For example Sponge coral don’t need light but some stony corals need a lot of light. You will soon learn what works in your tank.
• To create any display the minimum light I will recommend is 1 high intensity, full spectrum tube and 1 actinic tube.
• In most situations the more light the better because the photosynthetic coral will be able to use more energy.
• The more actinic lights you have in the tank, the fewer problems you tend to have with algae.
• Be careful the heat generated from the light shade does not affect the temperature of the tank too much. If you have more than one tube I strongly suggest you have a double light shade with remote ballast. This will keep most of the heat off the top of the aquarium. You can nail the ballast to the inside of the back leg of the stand.
• Mercury vapour lamps are better than fluorescent tubes because they generate less radiation, though they lack blue spectrum so they should be run with actinics as well.
• Metal Halide lights seem to give the best results for a reef tank.
• Metal Halide lights over 10000k don’t have to have an actinic, although it is better if you do.
• Metal Halides must have a radiation filter to minimise harm to you and your tank.
• The light that grows stony corals the best seems to be 10000K Metal halide. (Some halide can have a hum).
• The 03 actinic are better then the 05 actinic.
• Black light shades absorb light and should be avoided. White or sliver is better.
• Higher watts = higher lumens = higher lux.
• If you wish to find out the lux of you tank a lux meters can be rented from a camera shop.
• Most corals and desirable algae require over 10000lux.

How often should you replace your light tubes?
• The common aquarium tubes (or fish only tanks) needs to be replaced every 6 months.
• The high intensity full spectrum tubes need to be replaced at least every 2 years (you are better of replacing it more regularly e.g. once a year even better every six months).
• Actinic tubes need to be replaced every 9 months.
• It is a good idea to write the date you got the tube in your logbook or on the tube so you don’t forget when it needs replacing.
• Metal halides should be replaced every year.
• Mercury vapour globes need to be replaced every six months.

Do you need a light?
Fish and some corals don’t need light to survive though most corals and plants do.

Why do some corals require light?
Some corals require light to survive because the symbiotic algae within the coral require light to photosynthesize. The photosynthesizing symbiotic algae are what provide the coral with its nutrients and oxygen.

How long should you run your lights for?
• For a reef tank the total duration of light should be between 10 to 12 hours a day.
• For a fish only tank it is not really important.

How should you turn the lights on?
• It is best if the lights are on timers for a reef tank.
• The tank should not go from complete darkness to intense light because of possible stress to the inhabitants.
• Ensure the room light is on before the aquarium light is to be switched on, this should minimise stress. Switch off the tank light before the room light to allow them to get used to the dark.
• It is advisable to set the timers so that the actinic tube comes on a half-hour before and a half-hour after the full spectrum lights. This is to imitate dawn and dusk effect.
• If you have several rows of lights try and make it so that they come on and go off one row at a time.

What types of lights are available?
The best are Metal halides then Fluorescent tubes.

Mercury vapour lights can release excess UV radiation and are too yellow in colour, though they are good for plant growth.
Sodium vapour lights can release excess UV radiation and are too yellow in colour.
HQI metal halides- are the best as they have more blue spectrum and give off a more natural and better light in regards to growing corals or a reef tank.
HQI-NDL is fine for most corals but the fish may appear off colour.
Tungsten lamps are no good- they get hot, have a short life, an incorrect spectrum and are too yellow in colour.

How high should a Metal halide be from the water surface?
• It should be about 10 to 12 inches off the water surface because they get so hot.
• If the tank doesn’t have trouble with heat the light can be closer as long as there are no corals right at the top of the tank that may be affected by the temperature or UV.
• Metal halides don’t seem to actually burn the corals under any normal circumstances.
• If the tank is overheating the light may have to be raised or extra air circulation provided.
• Try to avoid the metal halide getting too close to your tanks centre brace because I have heard of them cracking if they aren’t made out of tempered glass.

How many Metal halides do I need?
On average 1 per 2ft x 2ft of surface area (if using 150w, 10000K). It depends in the size used.

How long should metal halides be on per day?
• They should be on for about 10 hours a day.
• If you have fluorescent tubes have them on for about an hour in the morning before the halide comes on and for about an hour after the halide goes off.

What size Metal halide should I use?
• Metal halides are commonly available from 75 to 400 watts, even 1000w.
• 75w is for under 18 inch high tanks.
• 150w is the most popular size, because these are best suited for 24-inch high aquariums.
• You should try to use 400w if your tank is 3ft high.
• Remember that the stronger the light you use, the more trace elements like calcium must be added to the water because they are used up be the coral quicker.

Can I use only Metal halide or do I need to have actinic tubes as well?
• No, a metal halide is able to maintain corals on its own if it is 150w or over.
• Metal halides are superior to actinic tubes for coral growth.
• But it is better if you do provide additional actinic lighting.

Can you use H.O. or V.H.O. tubes?
• Yes, you can but they require special ballast.
• HO tubes last longer than VHO.

Where should you place the light ballast?
• Keep it where heat build up won’t be a problem.
• Don’t let it get wet.
• It is often drilled to the inside of the back leg of the tank.
• Don’t put it under the hood.

How do you minimize UV radiation?
Plexiglass will filter some of the UV radiation.

Can you rely on direct sunlight to grow coral?
• This isn’t advisable because sunlight is unpredictable and seasonable.
• From one season to the next it is unlikely that the tank will receive even exposure to light.
• The main issue is that the water will normally be heated up too high as a result of the direct sunlight. So a large chiller would be required which would outweigh the price of the extra lighting anyhow.

What is the blue light?
It is an actinic (see glossary).

To grow corals are blue or white lights better?
• In general the more blue light you are able to offer, the better.
• The deeper the water that coral comes from, the more important the blue is because that is the only colour spectrum that is able to penetrate through any depths.

Are 50/50 light tubes any good?
• The only time I recommend a 50/50 tube is when you want coral but you can only have one tube.
• If having two tubes is not an option then a 50/50 is ok as long as you replace it every 9months.
• Remember the 50/50 has half intensity full spectrum and half-actinic, so it is obviously not as powerful as a tube each and maintaining particular corals is harder.

How do you create the ripple effect?
Spotlights set on an angle down from the top create a natural ripple effect.

What are colour wavelengths?
• Violet 400-420nm
• Blue 420-490nm
• Green 490-560nm
• Yellow 560-590nm
• Orange590-630nm
• Red over 780nm

by Paul Talbot


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