Comparing Fluorescent vs. Metal Halide Aquarium Bulbs

Lighting for aquariums is an incredibly complicated task. Too little light can endanger plant and fish life and growth, while too much light can lead to a high rate of algae growth. There is also a heat factor, in too much heat can kill fish and plants.

Aquarium owners will often combine several types of light sources to achieve the spectrum and intensity of light they are trying to achieve. Traditionally, fluorescent and metal halide have been the most common types of aquarium bulbs, although LED is making inroads.

In this article, we'll take a look at the benefits and drawbacks of linear fluorescent and metal halide bulbs for aquarium lighting.

Linear Fluorescent Aquarium Bulbs

Linear fluorescent aquarium bulbs are available in T5, T8, and T12 shapes. Fluorescent tubes use phosphors to coat the bulb, which can provide different light spectrums based on the phosphors used. The fixtures they are used in require a ballast, so changing bulb shapes or wattages would require a new ballast or whole new fixture.

Benefits

• Low Heat - Fluorescent bulbs do not output as much heat as incandescent or metal halide.
• Lower Price Point - Compared to metal halide or LED systems, fluorescent tubes are relatively cheap.
• Numerous Options - Because of the wide range of phosphors available, aquarium bulb manufacturers can create lamps in various lengths, wattages, and spectrums.

Potential Drawbacks

• Light Degradation - color temperature shift and diminished output can negatively impact the bulb before it burns out, potentially risking fish and plant life.
• Shorter Life Than LED - although fluorescent aquarium bulbs are rated for long lives, they will not last as long as LED bulbs or systems, although LED also suffers from diminished light output before lamp failure.
• Easier to Break - fluorescent tubes are more fragile than other light sources, so have more potential for breakage. Longer tubes over 4' will also be more expensive or inconvenient to transport.

Metal Halide Aquarium Bulbs

Metal halide aquarium lamps are common in plant/reef aquariums. They have a higher intensity, in general, than other light sources, and are available in higher wattages and color temperatures than fluorescent tubes.

Benefits

• Light Intensity - available up to 1000 watts, the light intensity of metal halide aquarium bulbs is unmatched by any other light source
• Highest Color Temperatures - while fluorescent tubes can reach 12000K or higher, metal halide can range from 10000K on the lower end to over 20000K, providing a deep blue light simulating sunlight in deep water environments . These are designed to promote photosynthesis in plant and reef aquariums.
• Color Rendering - metal halide lamps can provide a higher CRI than fluorescent, meaning colors are rendered more naturally.

Potential Drawbacks

• Light Degradation - metal halide lamps are also subject to color shift and diminished output as they near the end of their lives. Having a spare bulb on hand is never a bad idea, since light output can diminish slowly over time, making it difficult to notice.
• High Heat - metal halide aquarium lights, with higher wattages and higher intensity, will also produce higher heat. It will be important to consider proper thermal management when using these bulbs.
• Higher Price Point - metal halide lamps are often two or three times more expensive than fluorescent bulbs. They will also cost more money to operate, as they use higher wattages than fluorescent or LED light sources.

General Aquarium Lighting Tips

Fish Only

In fish-only tanks, visibility is the paramount concern, although preventing excessive heat is also important, especially in summer months. These aquariums can utilize more decorative lighting and ignore issues regarding plant photosynthesis.

Plants and Reefs

Lighting for plant and reef aquariums is much more complicated than for fish-only tanks. Plants and coral need the right types of light spectrum and intensity to thrive. For deep tanks, high output (HO) or very high output (VHO) lamps may be required to achieve optimum light depth and coverage.

No One Right Answer

Each tank differs in the presence of absence of plant life, fish, size, depth, and heating concerns. This makes it impossible to recommend a one-size-fits-all aquarium lighting solution. The light used should reflect the type of organisms in the tank, to promote beneficial growth and limit harmful concerns.

Know When to Replace Bulbs

While bulb manufacturers may recommend replacing aquarium lamps every 6-12 months, much depends on the aquarium. If the lights are on most of the time, replacement will be more frequent than if they were turned off, obviously. It is always our recommendation to have a spare bulb or two on hand in case one fails prematurely or if light degradation becomes noticeable.