Lighting - What does it mean?
Please note:This article and pictures were taken from my website and was written by Stephanie Abbott, if you wish to use this article please message me for prior permission.
Many websites and livestock sellers use very generic terms when describing the lighting conditions corals need in order to survive and thrive. The reason for this is that it's very difficult to sum up appropriate lighting requirements for corals, mostly because there are various types of bulbs and fixtures available as well as the height of a tank making a large difference.
Many times bulb "reflectors" will be mentioned when determining what category lighting you fall into. It is always recommended to get a lighting fixture that comes with INDIVIDUAL reflectors on each bulb, rather than one large reflector around all of the bulbs. Individual reflectors can increase light output by up to 300%! Don't have them on your fixture? A little DIY can go a long way... Many fixtures can be modified to have reflectors added to them for an instant upgrade to your lighting.
There is such a thing as too much light. Two 250watt halides on a 12" tank will not cause your acropora to grow faster... it will causes it to bleach and die.
Linnaeus uses the following terms when describing the lighting requirement for corals: low, moderate, high, or none (in the case of non-photosynthetic animals). Here are some guidelines to help you determine what category your current lighting falls under, separated by tank sizes.
*** PLEASE NOTE: This is only a rough outline. Nothing in this hobby is straight forward or predictable. For example: Some fixtures rated as "moderate" lighting may be able to support "high" lighting corals if placed very high in the tank and/or supplemented with additional food.
*** ALSO: We are assuming you are using the appropriate length of bulb for your tank... (i.e. 48" fixture on a 48" tank).
Very Short Tanks - Height: 10" (25cm) or less
Nano tanks have one large advantage to them, and that is lighting. Being so short, the most simple of lights can support corals that generally require much higher levels in taller tanks.
One power compact or T5 bulb should be enough to do just about any coral in a tank this tall. Because of the fixture having only one bulb, it should have its own reflector. This would qualify you as having high lighting.
For those of you with T8s, one bulb would be plenty for you to qualify as having moderate lighting.
LEDs have become more popular with smaller tanks. Something like Azoo's neo LED light or similar can very easily support soft corals (placing them into the low lighting category), however, I have not seen very good results with LPS corals even in the shortest of tanks.
Short Tanks - Height: 11"-15" (28-38cm)
A two power compact or T5 bulb fixture with individual reflectors should be plenty to qualify you for high lighting. For fixtures without reflectors, it is recommended to have at least 4 bulbs, with 6 bulbs being better to fall into the high lighting category. It may be possible to have only one bulb and to support high light corals, if they are placed very high in the tank.
A fixture containing one power compact or one T5 bulb with individual reflectors will put you into the moderate lighting level. Without individual reflectors, a unit with 2-4 bulbs will put you into this category.For the low lighting level, a single T8 bulb (standard in many hoods) will put you here.
Please note that metal halides are likely to be way over kill on the smaller height tanks, even for the "high lighting" corals. Too much light will cause fading and bleaching.
Medium Tanks - Height: 16"-19" (40-48cm)
The following would be considered high lighting for these tanks: standard metal halide unit, 4 or more bulbs of either power compact or T5s, each with individual reflectors. For those without individual reflectors, 6 bulbs of either power compact or T5 would be best to get into this category. With two bulbs with individual reflectors, high light corals may do well if placed up high in the tank.
To qualify for the medium lighting category, a fixture containing 2 power compact or T5 bulbs with individual reflectors would be needed. Without reflectors, a 4 or 6 bulb fixture would be needed.
For low lighting, a single power compact or T5 bulb would be adequate. 1-2 T8 bulbs may be able to support very low light corals (ie. Mushrooms and Zoas).
Tall Tanks - Height: 20"-24" (50-60cm)
Metal halide lighting (more commonly either 150 or 250 watt) would be considered high lighting for these sized tanks. Many tanks this size have a middle brace on top of the tank, therefore more than one metal halide is recommended (on either side of the brace), in order to prevent dim spots on the edges of the tank. 4 or more T5 bulbs with individual reflectors will be suitable for high light corals, as long as they are in the upper levels of the tank, otherwise 6 or more bulbs is recommended.
Medium lighting, 2-4 bulbs of T5 or power compacts with individual reflectors. 6 or more bulbs if no individual reflectors are present.
For low lighting, 2 Bulbs of T5 or power compacts will allow good growth for corals. As low as 2 T8 bulbs is possible for very low lighting corals (ie. Mushrooms and Zoas).
Very Tall Tanks - Height: 25" (63cm) or more
***Please note***: Because this is pretty much 25" to INFINITE height, suggestions here are not fixed and vary greatly depending on exactly how drastically tall the tank is.
With a tank so tall, nearly all people would opt to go with at least two metal halide fixtures (potentially more depending on the length of the tank). Multiple 250 watt fixtures should be plenty of lighting to do just about any corals. Additional bulbs of T5 would be great supplements especially for color.
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