The Importance of Lighting
Most novice aquarists underestimate the importance of lighting on their new fish environments. The average aquarium set-up contains one all-purpose bulb which implies that special lighting is not necessary.
Lighting is of VITAL importance to the marine aquarist and a high priority for tropical fish keepers if they wish to simulate a true under-water environment that is both healthy and visually appealing. Corals and invertebrates use lighting to regulate and assist in digestion, feeding, reproduction and growth. Plant aquariums need proper lighting in order for plants to thrive. A fish-only tank will benefit from correct lighting with increased coloration, activity and spawning.
The most obvious use of lights is to light the tank so that you can see your fish. Light spectrum runs from violet on the short end (320 nanometers) to red on the long end (700 nanometers). Remember your red, orange, yellow, green, blue, indigo, violet light spectrum? Below are two light bulb spectrums represented visually by peaks and valleys on a ROY G BIV scale.
The sun has 3 wavelengths: UVA, UVB, and UVC. UVA is the visible wavelength of light and is responsible for the "physiological well being" of fish. The 420nm blue (UVA) range is particularly important to marine corals and invertebrates and also helps stimulate feeding and breeding behavior in fish.
UVB is the non-visible wavelength of lighting. UVB is the spectrum which gives humans a suntan. This is a critical component for reptiles in that the 320nm range of violet (UVB) is needed for many animals to assimilate calcium into their systems.
UVC is the wavelength used for Ultraviolet Sterilizers which kill harmful bacteria. This wavelength is very dangerous to all animals.
Different spectrums are required for different species who dwell in different latitudes and at different water depths in their natural environments.
Full Spectrum Light/CRI Rating
Full spectrum light is a light source that emits all of the wavelengths of the visible spectrum in proportion to that of natural sunlight. To give you the best color rendition (CRI rating) and bring out the natural beauty of aquarium fish and plants in both freshwater and marine tanks, choose a daylight lamp with a full spectrum of visible light. A CRI as close to 100 (the CRI of natural sunlight) is desireable for visual affect. Its spectrum graph would have higher peaks in the middle of the spectrum with low ends.
The color temperature of light is the ratio of red to blue light waves measured in degrees Kelvin (K). At 6000 degrees (K), the ratio between red and blue is equal. The lower the content of blue light waves, the lower the color temperature. During the day, the color temperature of sunlight varies. It also changes at different depths underwater as reds are filtered out more rapidly than blues. A "K" or Kelvin rating of 5500-6500 is a good estimate to simulate a noon sun in most tropical fish environments.
Although blue spectrums penetrate deeper into water, species which live fairly deep rarely see the red end of the spectrum because it is filtered out by the water. They can actually be "bleached" to colorless by a light that is too intense.
Many reef inhabitants need much higher K values (blue end) from 10,000K to 20,000K for happy growth.
Stimulate Spawning & Appetite
In freshwater aquariums, you may add tubes with UVA emmissions (higher in blues) and you will begin to stimulate feeding and mating behavior in your fish.
New LED Lunar lights also simulate the day/night cycle and help to increase spawning. They create a tropical night-time full moon effect in your tank for your viewing pleasure as well as the health of the fish. Some can be added to already-purchased hoods and light strips. see: Lunar Lighting
To maximize the photobiological process in plants, add more red AND blue spectrum, as plants require both red and blue enhancements. The use of a floral bulb with a daylight bulb will give good visuals AND healthy plants. (Remember, if you use plant-enhancing daylight with added red and blue spectrums, you may also increase the undesireable algae growth in your tank, so don't enhance these spectrums unless you have adequate freshwater plants to battle for the algae nutrients)
Trichromatic bulbs are an excellent full spectrum daylight lamp and provide maximum daylight simulation. They are very good for freshwater tanks simulating 10-15 feet of water depth. This is best for visuals as well as brightness. Some trichromataics are also high in blue UVA emissions to stimulate feeding and breeding behavior.
Marine and reef tanks are VERY specific and require much more exact lighting spectrums. A minimum of two fluorescent light sources is always required, and even more tubes are often beneficial, as you can balance visuals and health needs more easily with more tubes.
Actinic light promotes the growth of Zoaxanthellae algae, essential for the growth and well-being of all photosynthetic corals and invertebrates (not macro algae). However, Actinic and strong blue spectrum lighting is visibly blue and will definitely need a full spectrum bulb to help offset the color distortion.
If your reef or marine tank appears too blue, balance its visible spectrum with a more intense daylight bulb or add another daylight bulb to the group. 5,000K-6,000K is usually pretty good. However, remember that macro algae can be a problem. Too much "daylight" (enhanced red spectrum = lower K value) will promote plant growth, and macro-algae responds similarly. A good rule of thumb is to use one actinic lamp and one or two daylight lamps for each 30 gallons of water.
The 50/50 bulbs were developed specifically for marine and reef tanks where the hobbyist wants the best of both worlds: healthy invertebrates as well as visual appeal. Most contain a bulb of about 6700K (for great visuals) and an actinic bulb (high blue) or a 10,000K bulb for much better blue-end-spectrum lighting for reef inhabitants. If you can't decide, go for one or two 50/50's.
Metal Halide Light
Metal halide lighting is the most concenterated and intense artificial aquarium lighting. It is partciularly well suited to deep planted freshwater tanks and saltwater reef tanks containing corals and clams.
Metal halide lighting adds a "sparkle" effect, as it replicates the natural reflection of sunlight bouncing off of surface waves and onto the reef below.
The largest drawback to metal halide use is the amount of heat generated by the bulbs. Essentially super powerful incandescent bulbs, they get extremely hot. They must be mounted 6"-12" (preferably 12") above the tank. Additionally, some type of heat dissipation technique must be employed to get rid of the heat that will over-warm the tank water. At the very least fans must be used. Usually a chiller is required.
Compact Fluorescent lights are essentially just a fluorescent tube bent in half to take up a smaller space. They are very beneficial because you can put more bulbs into the light strip space, adding more light and finely balancing spectrums without covering the entire tank top with bulbs.
One of the newer innovations in aquarium lighting, lunar lights are actually LED lights with a light-emitting diode which draws practically no current, generates no heat, and lasts a long time.
Probably initially developed as a way to enhance the visual appeal of an aquarium (kind of like black lights - which should never be used), lunar lighting has turned out to be very important. It is now well established that the lunar or low-light cycle for reef tanks is an important part of reef inhabitants' normal metabolic cycle. Under the influence of moonlight, many reef species actually grow and even more begin the reproductive cycle. Additionally, predators come out and prey species hide.
Until Lunar lighting, it was impossible to view your aquarium at night without distrubing the inhabitants with bright daylight lighting. Besides the fact that lunar lights make your tank into an entirely different visual landscape, the bright lights made it impossible to see what really goes on in low light environments. Some species actually fluoresce under lunar lighting.
Lunar l ights can be purchased already incorporated into high-quality multi-purpose light strips that contain other daytime spectrums, or they can be purchased as add-ons.
The "T" value of a fluorescent light is nothing more than the size (diameter) of the tube. T-5 bulbes are really skinny. T-8 tubes are middle sized (1" diameter). T-12 tubes are the fattest tubes (1.5" diameter) and look the most like tubes you are used to seeing in your office ceiling lights. Be sure to check which size tubes your tank takes before ordering them.
The color spectrum of a lamp changes with age. Although it may still look like visible light, the first wavelengths to go are the blue and UVB/UVA spectrums not visible to the eye. If your lights are not changed at least once per year (preferably every 6-8 mos) you are probably not getting the original spectrum of light for which the bulb was rated, and your tank inhabitants will suffer. The high-blue lights needed by reef inhabitants wear out much more quickly than standard fluorescent visible light tubes. YOU still see the light, but the reef is not getting the light it needs.
Deeper aquariums require extra lamps. A good rule of thumb is to add an extra lamp for each 15 inches of tank over 20 inches high so that adequate light reaches the plants or reef inhabitants which dwell on the bottom of the tank.
Glass filters out 95% of all UVB rays unless your tanks's glass top has been specially produced for high quality light penetration.
The amount of time that a tank is illuminated should closely resemble the native environment of the inhabitants. Since most are tropical, a 12 hour light cycle (12 light/12 dark) will be fine. There is rarely any need for your aquarium to be lighted for more than 12 hours, and longer daylight cycles can induce undesireable algae bloom