Aquarium 'moonlights,' e.g., LED (Light Emitting Diodes) lamps that emit a blue spectrum near 484 nanometers and actually duplicate the spectrum/light coming from the moon, first came to the marketplace in the very late 90's/early 2000's. While working with BrightLights Technologies at that time, which was the first company that I know of to bring these lamps to the marketplace, I was among the very first to utilize LED moonlights on aquariums. In fact, I can remember some very late nights sitting in front of my 125-gallon reef aquarium watching animal activity not seen during the daytime. I also remember trying several different 'polite' ways to make occasional guests realize it was time to go home, as my moonlights came on about 10:30 at night and their questions about activity in the now 'moonlit' aquarium sometimes seemed endless!
In today's aquarium world, most marine aquarists are very in tune with the light spectrum and intensity requirements of their daytime photosynthetic coral animals, and more often than not, also utilize a sunset/sunrise light timeframe that either slowly diminishes overall light intensity or slowly increases it to prevent animal shock when main lighting systems go on or off. Nevertheless, other than for aesthetics, they often seem somewhat less informed when it comes to the 'science aspects' of the moonlit timeframe. And that's the reason for this article, to discuss some of those and why it's more than just aesthetics.
As to those science-related aspects, besides tidal effects caused by various phases of the moon, Mother Nature has targeted its ocean shallow depths for eons with visible light from both the Sun and Moon. And because of that, there are major animal activity differences between daytime and nighttime, as there is in the species that encompass those timeframes. To define this further, scientists have placed these animals into three categories: Diurnal, Nocturnal, and Crepuscular.
As for those more active during daytime, they are called 'Diurnal' species, e.g., Angelfish, Butterflyfishes, Damselfishes, Gobies, Parrotfishes, Puffers, Surgeonfishes, and Wrasses to name only some. They mainly use their eyes to locate food, find their way through the areas they call home, and distinguish colors (even though some are color blind) to identify juveniles, the opposite sex or possibly a competitor or threat. At nighttime, they must find a safe place to sleep, yet many do not, but simply rest somewhere thought to be safe with their eyes open, as do all fishes, as they cannot close them since they do not have eyelids -- they are simply in a state of reduced consciousness. Some also produce a cocoon of slime to spend the evening in, such as some Parrotfishes, which helps deter nocturnal predators, or lodge themselves between the sharp spines of some corals or into small cracks in the reef structure, such as some Triggerfishes.
Then there's the nightshift, and those more active at night are called 'Nocturnal' and they include Cardinalfish, Eels, Groupers, Pinecone fish Scorpionfish, Snappers, Soldierfish, and Squirrelfish, to mention some. They are more solitary and prefer to stay in caves or under ledges during the daytime. Furthermore, they tend to have larger eyes than diurnal species (better to see in those dim conditions!), and also many tend to swim slower and are less colorful than diurnal species since it helps them blend into the low/dim level of actual moonlit environments. In fact, the color red is often seen on nocturnal fishes, e.g., Squirrelfishes, because this color becomes impossible to differentiate as the intensity of visible light levels decrease. Their very well tuned sense of smell is also a major asset as it helps find 'sleeping' prey in the dim conditions. Some, such as Lionfish/Scorpionfish, have a more developed lateral line, which gives them an improved ability to sense very slight water movements, which aid in finding prey in low light conditions. Also, nocturnal fish tend to be mostly carnivores, whereas diurnal species are more herbivores or omnivores.
Even some invertebrates fit into the 'Nocturnal' category, e.g., lobsters, shrimp, octopus, and crabs, as do other invertebrates such as worms, Seastars and urchins, and also the polyps on many corals that mainly feed during evening hours when plankton is normally more available. There is also another category that pertains to those especially active at dusk and dawn, and they are referred to as 'Crepuscular,' such as Goatfishes. There are also certain fish and invertebrate species that recognize moon-related cycles, which induce spawning. It seems Mother Nature has bred this more active time period into the genes of these animals for one very good reason, among others -- it's the time when 'their' food supply is the most available - and then added some physical attributes to enhance their skills and on-going survival.
So what do these differences mean to the aquarist and how do they relate to a moonlit aquarium environment? Good questions, as it's important to the animals in all three categories, and of course, the aquarist's overall visual pleasure. And since aesthetics are probably the number one reason why the aquarium moon-related lighting timeframe has been so successful, lets examine it first. - Picture in your mind swimming through a moonlit lagoon. Great isn't it! Unfortunately many have not been fortunate enough to experience such an exhilarating experience. But I can relate to that experience, and still remember seeing shimmering moonlight on the underwater reefs! And not until 'moonlights' became available was I able to duplicate that vision in my reef aquariums. No doubt a personal satisfaction, but one that also goes hand-in-hand with why we get into this educational hobby, as moonlights help provide an inexpensive way to create a more overall natural environment, whether it's in a fish-only or reef aquarium. And that's the goal of all aquarists (or should be) - to create a more natural aquarium environment!
Another reason to equip one's aquarium with moonlights is that some very 'normal' processes that the animals in all three categories have are affected by the phases of the moon/spectrum provided by the moon. Take away this natural trigger mechanism and some health aspects of the animal will be affected. And I've seen changes to some coral animals after being lit by moonlights for ten months that I've never seen in aquariums prior to systems without moonlights, such as my Yellow Leather coral, Sarcophyton elegans producing polyp-like structures on its 'underside' that eventually dropped off forming new daughter colonies! Also, my very large Chalice or Cup Coral, Turbinaria peltata, also developing a series of projections along its underside. Whether or not the moonlighting was responsible for these reproduction activities is not a question I can honestly answer. However, I've had these species in other aquariums years before moonlights became available, and never saw such interesting growths.
And when it comes to stocking the aquarium with fishes, be aware of the species natural environment and main activity timeframe. Keep in mind if it's a naturally nocturnal species and will be in a mixed species/community/diurnal environment that is fed during daylight hours, it opens the door for health problems for the nocturnal species if they do not get their share of the offered foods. Furthermore, if that occurs, bad behavior follows as they are forced by hunger to attack other more docile tankmates during evening hours. In fact, I've had letters from those that put some of the larger Squirrelfish species as juveniles in their large multi-species aquariums only to have their smaller fishes slowly disappear as they grew to adulthood! Therefore, keep in mind final size if choosing a juvenile nocturnal carnivorous specimen, as other smaller species in the aquarium could sooner or later, become breakfast, lunch or dinner (on their schedule)!
Since there's no doubt some of the species normally maintained by some aquarists are nocturnal, and their functions are better seen during evening hours, a system without moonlights is actually doing them a disservice. In fact, all animals in the aquarium! It's also opening the door to health problems, which could eventually affect all species in the aquarium.
As to moonlight timeframes, in my opinion, its better limiting it to nothing more than 10 hours per day, similar to what occurs in the wild. As an example, the following are my system schedules: main daytime lights - MH lamps come on at 12 noon and go off at 10:30 pm. Sunrise/sunset actinic fluorescent lamps come on at 10 am, and go off at 11 pm (this adds to the overall available light in the aquarium during daytime use of MH lamps). Moonlight LED lamps come on at 10:30 pm and go off at 6:30 am. Only natural daylight enters the aquarium during the 6:30 -- 10 am timeframe. The cycles then repeats and have found this scheduling to nicely fit the wide variety of aquarium environments that I've had over the past decade, and for most of those who have contacted me with similar lighting questions.
When it comes to selecting lunar/moonlights, LED lamped or an actinic fluorescent lamped fixture can be utilized to create the moonlit timeframe. As to LED lighting technology, it generates very little heat, e.g., probably only slightly above the temperature of your normally maintained tropical aquarium, and the lamps should last at least 50,000 hours without any significant decrease in spectrum or intensity. And past information on these lamps had them lasting up to 150,000 hours with only minimal reductions in their spectrum and intensity! In fact, I'm still using the LED 'review' preproduction moonlight model called 'MoonBeam' for 10 hours daily that was sent to me about a decade ago! Of course, actinic fluorescents can't make that statement, but I've used them on some past aquariums quite successfully in my opinion.
However, LED lamps provide one visual benefit fluorescent lamps do not, and that is pin-point focus of its light energy which results in glitter lines on the substrate during the moonlit timeframe, as seen in the wild and discussed above. Fluorescent lamps are designed, because of their length, to spread out its intensity/spectrum, thereby distributing its light over a wider area/not a more focused light shaft capable of producing glitter lines.
Presently, commercial lighting fixtures capable of producing the moonlight spectrum range from fixtures solely containing LED blue lamps to fixtures combining other light sources and ways to control the entire range of aquarium lighting requirements, such as those equipped with microprocessor controlled circuitry and LCD illuminated controller panels that can program moonrise, moonset, phases of the moon, cloud simulation, automatic dimming or intensity increases (sunset/sunrise intensity periods), and even letting the aquarist know when its time to replace fluorescent or metal halide lamps! For those that like to do it themselves, LED lamps themselves can be purchase on-line or possibly in a local Radio Shack store along with the other odds and ends needed to assemble a fixture.
Remember, you get what you pay for -- simply blue light, or the wavelength and intensity and 'focus' needed to replicate moonlight seen in the shallow ocean depths -- and -- possibly the other niceties some products offer! And yes, you could blue light your aquarium for far less than 100 dollars, then again, spend a few thousand dollars for an all-out model. The choice is yours.
To sum it up, there's no doubt animals have developed certain lunar-related characteristics, such as a 24-hour clock built into their makeup, e.g., some wrasses sleep under the substrate in the wild and go to sleep at the same time every evening and awake and leave the burrow at the same time the next morning. And when transported from their natural surrounding, still bury themselves at the exact same time in the aquarist's aquarium that they would have in the wild, even though it may be mid daytime in the aquarium! And yes, this nighttime burrowing behavior will slowly change and be more in tune with the lighting in the aquarium, but it does prove the 24 hour clock is built-in. Therefore, this and other natural time/lunar-related characteristics should be taken into consideration when populating the aquarium. In fact, equipping the aquarium with a moonlight fixture, which can be initially quite inexpensive and also inexpensive to operate and maintain, is simply commonsense, besides the additional viewing pleasure!