They must get about 10 hours a day average, however I must admit I have been guilty of occasionally forgetting to turn them on before I go to work, or falling asleep and having them on all night. I will be putting them on a timer soon, how long would you suggest to have them on? I usually leave my blue LEDS on overnight so will not include them on the timer.
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I would get a timer, the type sold for table lamps is fine. It is important to have a fairly regular period of light/dark each 24 hours, not only for plants but even more for fish. Uneven light periods can cause stress to fish. I would also not leave the blue LED lights on at night. These are OK after the main tank light goes out, for a "dusk" effect of an hour or two, but then it should be total complete darkness for several hours. I will explain why momentarily.
A period of 8 hours or so of tank lighting (the full "daylight" lighting) each day is probably best, though you can go over this a bit, keeping an eye on algae. The plants cannot use the light if nutrients are insufficient, even one nutrient, so it is important to find the balance of light/nutrient supplementation that keeps the plants happy and doesn't encourage algae. Now to the light issue, for which I'll cut/paste an excerpt from an article I authored for another forum.
Most animals have an internal body clock, called a circadian rhythm, which is modified by the light/dark cycle every 24 hours. This is the explanation for jet-lag in humans when time zones are crossed—our circadian rhythm is unbalanced and has to reset itself, which it does according to periods of light and dark. Our eyes play a primary role in this, but many of our body cells have some reaction to light levels. In fish this light sensitivity in their cells is very high.
The rods and cones in the eye shift according to the changes in light. This process is also anticipated according to the time of day; the fish “expects” dawn and dusk, and the eyes will automatically begin to adjust accordingly. This is due to the circadian rhythm.
This is one reason why during each 24 hours a regular period of light/dark—ensuring there are several hours of complete darkness—is essential for the fish. In the tropics, day and night is equal for all 365 days a year, with approximately ten to twelve hours each of daylight and complete darkness, separated by fairly brief periods of dawn or dusk. The period of daylight produced by direct tank lighting can be shorter; and the period of total darkness can be somewhat shorter or longer—but there must be several hours of complete darkness in the aquarium. The dusk and dawn periods will appear to be stretched out, but that causes no problems for the fish. It is the bright overhead light that is the concern, along with having a suitable period of total darkness, meaning no ambient room light--as pitch black as possible. And the "day" period when the tank lights are on should be one continuous period, not sporadic, and it should be the same every 24 hours or it will impact the circadian rhythm causing more stress.
Byron.
