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The Lighting Cycle – What Is It

Written by John Cunningham · Filed Under Aquarium Lighting 

October 20, 2007 · Print This Article

Our everyday lives are controlled by time. We may not like it but that is how it is.
On the wild reef things are much the same. I know, reef life doesn’t have a lunch hour! What they do have is dawn, day, sunset and night.

Life on the reef is controlled by these changes in light intensity. Daylight fish prepare to disappear into their secure holes when sunset arrives. Night life prepares to emerge. At dawn it reverses.

The instincts of marine life do not change when that life is in a home marine aquarium. The light cycle still dictates to them. In the same way that aquarists wish to run their systems as close to nature as possible (live rock, DSB’s etc), it is very desirable to attempt to copy the light cycle of the reef. Aquarists call this the [tag-tec]lighting cycle[/tag-tec], meaning the actions their lighting system follows as time progresses. The benefit is to fish and other mobile life forms, and also to corals. The changing light also makes aquarium watching more interesting to the aquarist.

So it is obvious that there is going to be a dark period (night), a subdued light period (dawn), an all lights on period (day), and then a subdued light period again (sunset).

There are some very sophisticated lighting systems available that can produce the above ‘out of the box’. However, let’s look at a more typical system in use, one that is perfectly adequate.

The lights provided for the marine life in the aquarium depend on the type of life it is, and could be high intensity from metal halides or lower intensity from fluorescent tubes. It makes little difference; the lighting cycle can be achieved easily with both. If only a metal halide is in use, then it is necessary to purchase one or better two fluorescent tubes, with a spectrum known as [tag-ice]actinic blue[/tag-ice]. These are easily obtained. Some metal halide units come with fluorescent tubes fitted. With a fluorescent tube array, it is necessary for one or better two of the tubes to be actinic blue. The aquarist will also need two electric timers. These also are readily available, and should be of the plug in type.

So, let’s achieve the lighting cycle then. The aquarist knows how long his main lighting period is going to be, usually 9 to 12 hours. It is best that the lights are on when the aquarist is there to see the aquarium, pretty obvious really! Knowing the required lights on period in hours, decide when the lights are required to switch on.

The actinic fluorescents power supply is routed through an electric timer. The timer is set to the lights on time less 30 minutes. In other words, the blue actinic fluorescents will activate 30 minutes before the main lights. The main lights power supply is routed through the other electric timer, and the timer is set to switch on at the point 30 minutes after the actinic fluorescents came on.

At the other end of the ‘day‘, the main lights are set to switch off after the number of hours of the decided upon main lighting period. The electric timer for the actinic fluorescent tubes are set to turn off after a further 30 minutes.

Definitely simple. So the sequence in the lights is blue lights come on, fish wake up, corals begin to inflate, nightlife hides away. 30 minutes later the main lights switch on, and ’day’ is there for the main lighting period. At the end of the main period, the main lights switch off, leaving the blue lights on. Fish prepare to hide in the rocks, and night life begins to become active. Corals begin to deflate. 30 minutes later the blue lights switch off and night has arrived, and will last until the blue lights switch on again at the start of a new ’day’.

Though not necessary, a third electric timer can be added if desired. This controls ‘[tag-self]moonlight[/tag-self]’ lighting (usually a very small array of blue LED’s). This switches on 15 minutes before the blue fluorescents switch off for the night. The ’moonlight’ puts very weak light into the aquarium and enhances the lighting cycle effect further, and in addition makes a very attractive sight for the aquarist. The ’moonlight’ can be left on for 2 hours or more. The cost of running them is very low.

The fish soon learn when night is approaching and can be seen preparing to settle for the period. The same when the blue lights first come on, they peer out of their secure hideaways making sure all is well before venturing out. It works very well, and gives the livestock a reasonable resemblance of lighting changes to match their instincts.

Definitely better than suddenly bathing the aquarium in bright light, or perhaps worse plunging it into instant darkness.

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