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Aquarium Lighting 101

Aquarium lighting serves many purposes other than illuminating and enhancing the appearance of your tank. Having the right lighting is vital to the health of your fish, plants, invertebrates and other livestock you may have. The rule of thumb is you want to simulate the lighting that best matches your livestock's natural environment. With ever evolving technology, you have a wide range of lighting options for your aquarium. Here we will discuss the different lighting terminologies and what they mean as well as all the different lighting types to help you select the one that is perfect for your tank.


Light Spectrum - The Kelvin Scale
The light spectrum or also known as the "temperature" of your aquarium lights is measured in degrees Kelvin (K). This measurement is based on the color of a light source that is compared to a "black body." (in physics, a "black body" is an idealized object that absorbs all electromagnetic radiation falling on it. Black bodies absorb and re-emit radiation in a characteristic pattern called a spectrum) So to summarize in more simpler terms. The Kelvin scale measures the temperature or defines the color of the light given off in comparison to the black body radiating at the same temperature.

To compare different types of light on the kelvin scale, we can say that at 0 degrees Kelvin, the theoretical black body emits no light. The Kelvin scale starts off being red as it warms. As it climbs the colors go to yellow, then green, blue, and finally violet. So reddish light will have a lower degrees Kelvin and bluer light will have a higher degrees in Kelvin.

Light Intensity - Lux & Watts
The intensity of light is measured at two different places. At the source which is measured in watts, and at the surface it impacts which we will measure in Lux.
  • Watts - The intensity of light at the source is measured in watts. The higher the watts, the more intense the light will be, and more energy will be required to produce the light. So a 60 watt bulb will produce a more intense light and consume more energy than a 40 watt light bulb. Higher wattage bulbs will cost more to operate.
  • Lux - We use Lux to measure the intensity of light at the surface of which it hits. For example, the intensity of the sun on the waters surface can exceeds numbers of 120,000 lux!

    The clarity of the water that the light hits also plays a factor in the lux number. For example, if light hits a reef with clear water it will average about 20,000 lux at around the depth of 15 ft. and around 10,000 lux at 30 ft. If the water clarity is sub par, it may lower the lux number to 15,000 lux at 15 ft and 8,000 lux at 30 ft. Over time your bulbs will begin to wear out and that will also diminish the intensity of the light giving you a lower lux number as well.

    We recommend getting a lux meter so you can check your lighting to make sure you are getting the right intensity to your aquarium as well as know when it is time to replace your bulbs.


  • (K): Kelvin - When you see Kelvin or K, it stands for the temperature or color of the light that you see. So a light that is described as 14,000k will have a bluer light than a light that is 8,000k.
  • Watts - This is the measurement of the intensity of the light bulb at the source. So the intensity of the bulb right at the bulb. A bulb in the same category (florescent, led, metal halide), with a higher wattage will provide a more intense light and will consume more energy. So if you are looking for energy preservation, you will want to obtain a lower wattage bulb.
  • Lux - this is the measurement of the intensity of the light at any point that it hits. So in your aquarium, at the surface of your water it may be 15,000 lux and as the light travels through the water, it may be 10,000 lux at the bottom of your aquarium.


When choosing your lighting system, you will want to pay attention to the type of bulb you're getting, the initial cost and operating costs, the heat produced, and is it sufficient to promote a healthy aquarium environment.
Here we will discuss the different varieties of lighting, helping you choose which one will be right for you.

Incandescent Lighting Systems are probably the most common form of lighting used in households. Your typical screw in light bulb you use is probably an incandescent one. These bulbs consist of a filament encased in a glass bulb. When electricity is passed through the filament, it heats up and glows producing light. This form of lighting is very inexpensive, can last for long periods and may also come in a variety of colors. This form of lighting is useful for smaller tanks that contain fish only. If you have live plants or coral, you will need a lighting systems that has a wider spectrum and higher light intensity.

Fluorescent Lighting Systems is probably the most popular form of lighting used due to the large variety sizes, wattage, color, and spectrum range. There are many types of fluorescent(s) starting form your typical standard fluorescent suitable for plants and coral that require low light. To your Very High Output(VHO) fluorescent systems that have a much higher spectrum and are great choice for your reef aquarium. Fluorescent light bulbs are gassed filled glass tubes. When a electric current is passed through the bulb, the gas is heated until it emits a light. To achieve different spectrums of light, the inside of the bulbs are coated with different blends of phospors. When the light that is emitted from the gas passes through the coating, the phosphors will produce different colors depending on the chemical make. Fluorescent light is more costly than incandescent lights, but are far more efficient. Below shows the different varieties of fluorescent lighting systems.

Standard Fluorescent Lighting or also called normal output(NO) fluorescent lighting are popular for aquariums that only need low intensity lighting. They come in a variety of colors including full spectrum daylight bulbs to partial spectrum color bulbs. These bulbs can range in length anywhere from 18 inches to 72 inches. You will often see these bulbs having a T-rating which is the method to describe the diameter of the bulb. So for example, bulbs that are T-8 are smaller in diameter of bulbs that are T-12. These happen to be also the most common sizes in aquarium use. Standard or NO output fluorescent lighting is a good choice for freshwater or saltwater fish only aquariums. If you have live plants or corals that require very low light intensity, having more than one standard fluorescent bulb system may be sufficient.

T-5 HO (high output) & VHO (very high output) Fluorescent Lighting systems are similar to your normal fluorescent lights in design, but offer a much higher light output. Due to the higher output, they need require a completely different ballast and end caps that are not compatible with the standard fluorescent lights. These lights are typically used in saltwater reef aquariums due to their capabilities of a higher kelvin and wider light spectrum. Though now, they are widely used in all applications from freshwater lighted aquariums to saltwater.

Compact Fluorescent Lighting systems are very similar to the other fluorescent systems, but they use a twin tube design to allow for more bulb in a smaller space. Compact Fluorescent lights are smaller in size, consume less energy than conventional fluorescent lighting and have a higher light output. They differ in design by their twin tube u-shape design and also either have a straight across pin or a square pin socket design. Compact fluorescent lights are a great choice for any aquarium setup due to there low operating costs and wide variety of spectrum s. They are also great with the combination of a Metal Halide bulb, which is often used in Marine Reef setups. .

Metal Halide Lighting systems are great for aquariums that need a really high light intensity. This type of lighting is great for saltwater reef aquariums or freshwater planted aquariums. Metal Halide lighting is also used for very tall deep aquariums that need a very high light intensity to illuminate all the way to the bottom.
Metal Halide bulbs are comprised of the outer main bulb with a series of wires connecting to a smaller glass bulb (arc tube) within it. When a electric current is run through the arc tube, the gases and metal salts inside the tube produce a highly intense light. The metal halide bulb has a base that looks like an incandescent bulb but require special socket system called a mogul. Metal Halide systems also require a larger ballast that is usually housed below the aquarium inside the stand. This lighting system does emit a lot of heat so a chiller is often recommended to maintain proper water temperatures. Metal halides come in a wide range of spectrum s starting from 4,000K all the way to 20,000K, as well as wattage ranging from 175 watts to 1,000 watts.

Note: this system may be have high initial costs in addition to higher energy consumption resulting in higher energy cost. The need for a chiller to maintain proper water temperature is also recommended.

HQI or Halogen Quartz Iodided systems are fairly new, but popular for saltwater reef aquariums. They are mostly offered in 150 - 250 systems with spectrums of 10,000K and 20,000K. The great thing about this system is the lower heat emission in comparison to tradition Metal Halide bulbs with the same Kelvin. These bulbs are also much smaller than metal halides and are double ended, requiring a special system specific socket. Though this system is great, there are some cons. The bulbs do give off less heat than regular metal halides, but they still get extremely hot and may explode if splashed with water. So you will need a glass covering over the water to prevent any unwanted splashing to reach your bulb. Also the HQI bulbs emit UV rays so you will want a glass covering over your tank that has a UV protection layer to prevent your coral from getting burned.

Note: this system may be have high initial costs in addition to higher energy consumption resulting in higher energy cost. The need for a chiller to maintain proper water temperature is also recommended.

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