Aquarium Lighting Tips

If hobbyists select the wrong type of lighting for a home aquarium, it can result in algae overgrowth, die-off of benthic plants, poor visibility and behavioral problems in fish. Fortunately, the challenge of lighting an aquarium is simple to address when the needs of the aquarium are taken into account. A proper lighting setup can make the difference between an unattractive, imbalanced aquarium and a beautifully aquascaped paradise.

Evaluating Biotope
The most successful aquariums are not hodgepodge “community” tanks; they instead combine fish that require similar water parameters and tank setups. These natural-environment tanks (called biotope aquaria by enthusiasts) mimic the lighting and water chemistry of wild aquatic ecosystems. To select a proper lighting strength, aquarists should research the lighting needs of each resident fish species. Some popular fish, like zebra danios, thrive under very bright lights. Others–including most tetras and cichlids–become shy, sulky and dull-colored in the presence of bright lights. Lighting requirements should suit the biotope of every species in the tank.

Selecting Kelvin Rating
Aquarium lighting fixtures are usually labeled with a Kelvin rating. This rating is a number–usually 5,500, 6,500, 10,000 or 20,000–followed by the letter K. Kelvin ratings indicates the wavelength or color spectrum provided by the lighting fixture. Shorter wavelengths, like 5,500 and 6,500, provide a reddish or yellowish cast, and longer wavelengths are blue-violet in color. Most aquatic plants can thrive under lights with shorter wavelengths, but reddish-toned plants and coral reefs require the ultraviolet rays found in 10,000 to 20,000 K fixtures. Additionally, tall tanks may need higher-Kelvin lighting because longer wavelengths are able to penetrate deeper water.

Timing and Cycling
Most fish and aquatic plants need anywhere from 10 to 14 hours of lighting per day. Too much light can cause fish to develop behavioral problems and may encourage the growth of algae; too little lighting can cause plants to die off. It is critical to set up a regular and predictable lighting schedule. For very sensitive biotopes, it may be necessary to set up a timer. While fish from dark, tree-shaded environments do not require a “night light“, fish native to open-water ecosystems can sometimes benefit from a whitish LED-based fixture that imitates moonlight. Breeders and professional aquarists may also adjust lighting times to mimic seasonal and lunar cycles; this can encourage temperamental fish to breed.

The right aquarium lighting can extend the health of your fish and encourage aquarium plant growth

The right aquarium lighting can extend the health of your fish and encourage aquarium plant growth, too. The wrong lighting or too little lighting can stress fish and even disrupt their life cycles. Aaron Hill explains, “Lighting not intended for aquariums lacks wavelengths of the daylight spectrum important to the health of your organisms, while including wavelengths that promote algae growth.” Focus first on creating the right lighting for your aquarium by considering the fish, plant or coral’s requirements and then add extra lighting enhancements to create unusual aquarium lighting for your observation pleasure.

Create a plan to address all the lighting needs for your fish and other aquarium life. Responsible fish owners will aim to simulate the natural environment as much as possible and use unusual lighting as an enhancement for observation but not as a main source unless the unusual lighting selected simulates the natural habitat.

Research the natural light requirements of your particular fish, aquarium plants and corals. Also consider the depth of your tank–deeper tanks may need stronger lights to penetrate into the depths of the fish tank.

Decide on the unusual aquarium lighting effect you are looking for: to enhance the color of your fish, to change the look of the water, to create a shimmering water effect similar to shallow waters outdoor or to add some light colors to the tank just for a fun effect. You may be able to achieve the effect you desire when you match up the right lighting with your particular fish or aquarium life. For instance, many fish lights that replicate night will cast a cool blue glow into the tank, which will enhance the colors of some fish.

To enhance the boldness of stripes or color contrast of your fish or to make light-colored or white fish stand out against a dark wall, backdrop or dark plant life, add a light fixture with a clamp to shine a black light bulb into the tank.

To replicate the shimmering water effect found in professional saltwater displays using metal halide lights, set up an LED lighting system instead. Unlike metal halides, the LED light system does not generate much heat, requires no cooling fans and and can help replicate the night and day cycle.

To create other colors in the tank or to cast other colors on white or light-colored fish, use an LED aquarium light system that can be fitted with white, blue, green and red lights and fully submerged in the fish tank for total control on where the light is cast. Or add additional light fixtures with clamps that hold incandescent bulbs in the colors you desire. Just remember that incandescent lights are great for color effects in your aquarium, but do not meet the natural day and night lighting your fish need.

Set up an aquarium light timer to go off every 12 hours so that you are reminded to manually change the lighting to create a natural lighting cycle. You can substitute an alarm clock for the timer.

LED Aquarium Light Intensity

Engineering advances in both LED and associated lens technologies have resulted in some rather amazing breakthroughs and these are becoming available to consumer markets. The LEDs used by AI are among the ‘brightest’ available. See Figures 9 and 10 for details.

Figure 9. The light produced by the Aqua Illumination LED array is quantifiably ‘bright.’ Note the distance of the PAR sensor from the luminaire (5”) – holding the sensor closer to the luminaire saturated the sensor. In other words, the LEDs produced more light than the sensor could measure (1,999 µmol·m²·sec – the intensity of sunlight at noon on a cloudless day).


Figure 10. Light intensity you would see at a water depth of 14.25” in an aquarium. The luminaire is about 1” above the water surface (with the supplied legs removed).

Light Production: LED versus Metal Halide

How does the AI LED array’s light intensity compare to that of a ‘traditional’ light source (such as a high Kelvin metal halide lamp)? An XM 250-watt 20,000K metal halide’s light output (PAR) was compared to that of the AI LED luminaire (see ‘Methods’ for details). In a nutshell, the LED array out-performed the 250-watt metal halide.


Figure 11. Light intensity (Photosynthetically Active Radiation, or PAR, reported in units of micromol photons per square meter per second) of a metal halide lamp. Compare these numbers to those in Figure 9.

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Photosynthetically Usable Radiation

Photosynthetically Usable Radiation (PUR) is an important, but not an ultimate, concept. PUR differs from PAR (Photosynthetically Active Radiation) in that PUR considers not just light intensity, but also the spectral composition of light. In order to estimate PUR, we have to consider which portions of the visible spectrum are actually absorbed by zooxanthellae. Fortunately, researchers have determined this, and call it an ‘action spectrum.’ An action spectrum describes the relative effectiveness of energy at different wavelengths in producing particular biochemical or biological responses (such as oxygen evolution, carbon uptake, electron transport rate, etc., during photosynthesis). Hence, or our purposes, we will consider PUR as those wavelengths falling between 400-550nm (absorption bandwidth of chlorophylls a, c², and peridinin) and ~620-700nm (red absorption bandwidth of chlorophylls a and c²). Figure 12 demonstrates the action spectrum of zooxanthellae isolated from the stony coral Favia.

Using these ranges, 74.7% of PAR produced by the AI unit is actually PUR and is therefore light usable by zooxanthellae and plants. It should be noted that light not absorbed by photopigments and the coral animal is reflected and results in our visual perception of ‘color.’ I think most hobbyists will likely prefer a visually-pleasing light over a photosynthetically-efficient light (which would appear reddish-blue in color).

My point is that we, as hobbyists, shouldn’t get carried away with this concept and PUR is more of a factor in low-light (photosynthetically sub-saturating) intensities.


Figure 12. Zooxanthellae and their photopigments ‘prefer’ certain light wavelengths for photosynthesis.

An in-depth discussion of PUR and its relation to photosynthesis under conditions of photosynthetically sub-saturating and saturating light intensities is well beyond the scope of this article. However, it does deserve attention and will be the subject of a future article.

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