You want or have a saltwater aquarium, but you have a lot of questions about lighting.

You would love to know which bulbs will bring out the beauty of your fish and coral, but also want to promote their health and growth. We are here to help with those questions. Reef lighting is a big decision with a lot of variables. We’re hoping this article will help you understand how to choose the best lighting for you.

You have a wide variety of bulbs to choose from. You could buy bulbs, mixing-and-matching until you find the right combination. But, we’d love for you to get those results the first time. While everyone has unique preferences, our hope is that this guide will assist you in finding the look that is most pleasing to you.

There are many ways to describe saltwater aquarium bulbs.

Perhaps the most important term for our purposes is color temperature. This rating has nothing to do with the physical temperature of the bulb or the heat it produces. You have probably heard something like this to describe household lighting. You might use a ‘warm’ bulb in your living room and a ‘cool’ bulb in your kitchen. These terms describe the color temperature, or Kelvin rating of the bulb. The lower the Kelvin rating on a bulb, the warmer it will be. A warm bulb will be somewhere around 3-6,000 Kelvin. As the number increases, the bulbs become ‘cooler’ in appearance. So, a 10,000 Kelvin bulb (10k for short) will be bright white with a hint of blue. As the color temperature rises, the bulb becomes bluer.

When choosing reef tank lighting, it is helpful to think about an actual ocean reef.

Right under the surface of the water, the color temperature is around 10k, a bright white with a touch of yellow from the sun and a touch of ocean blue. This oversimplifies the science, but is a helpful visual. As you look deeper in the ocean, yellow and white light is filtered out by the water. So, the deeper you look under the ocean the bluer everything appears. This happens because certain wavelengths of light are filtered out as water depth increases.

The first question you should ask yourself is “what sort of reef do I want to replicate?” If you go with a 10k, reef top look, your tank will have a full range of colors, but less fluorescence. If you go for a 14k, mid-reef look, some colors will be muted but there will be more fluorescence and vibrancy. If you choose a 20k, deep reef look, you will get a ton of fluorescence and deep coloration, but certain colors will be muted. Most hobbyists choose something between the 14k and 20k look, but go with whatever pleases you.

Before we proceed, there is something very important to understand about using color temperature to choose a bulb.

While measuring Kelvin sounds scientific (and really ought to be), there is a lot of variance in the industry. What one manufacturer calls deep blue 20k looks just like another manufacturer’s 14k. While this can be frustrating, there is a general rule that might help you choose. Bulbs from American and Asian manufacturers tend to be bluer than bulbs from European manufacturers. This makes sense, because American and Asian hobbyists tend to prefer bluer tanks than their European counterparts. So, what is really blue to a European’s eye is moderately blue in America.

Fluorescence is another factor to consider.

There is a special type of bulb, called an actinic, which you might compare to a ‘black light.’ An actinic bulb focuses light in the wavelength at which many corals and fish fluoresce. ‘Pure,’ ‘true’ or ‘super’ actinic bulbs peak at the 420nm wavelength, which renders a dim purple, barely perceptible to the human eye, that produces the most fluorescence. Blue actinic produces more visible light, but cause less fluorescence. While these bulbs do help some with photosynthesis, their primary use is to make the aquarium livestock pop with vibrancy. LED actinics are particularly effective at this.

Many bulbs (and particularly LED fixtures) are combinations of different types of bulb. For example, a 60/40 actinic is 60% blue and 40% actinic. LED fixtures achieve similar results by combining different color LEDs.

Another important factor is photosynthetically available radiation (PAR).

Most corals are photosynthetic animals. In order to thrive, they need plenty of light energy to take in nutrients. The higher the PAR rating of a bulb, the more energy is being transmitted to the coral for photosynthesis. This is important because yellow and white bulbs tend to produce the most PAR. So, even if you want a very blue tank, you need to ensure that you are not starving your corals by your bulb choice. Thankfully, these days blue bulbs tend to produce a fair amount of PAR, making the task less worrisome.

As far as the type of bulb you choose, there are three main choices: metal halide bulbs, fluorescent tubes and LEDs.

Metal halides are an older technology that use more electricity and produce more heat. But, they also produce a lot of PAR. Furthermore, they are great for very deep tanks because the light penetrates so far. In most applications, you would want 1 metal halide bulb for each 2 feet of tank length.

Fluorescent bulbs are described according to their thickness. T12 bulbs are the thickest, T8 is the average size you are probably used to, and T5 bulbs are about as wide as your finger. Fluorescent bulbs are categorized as normal output (NO), high output (HO) and very high output (VHO). You will also see some bulbs marked V-HO, for variable high output. Be sure to purchase the right output and diameter bulbs for your fixture. The higher the output rating, the more energy the bulbs can take. This increases brightness and PAR. T5 HO bulbs are the most common in the hobby. Their thin diameter makes it easy to put reflectors behind each bulb, greatly increasing efficiency.

LED bulbs are a newer technology that has rapidly grown in popularity. There are several advantages to LEDs including energy efficiency, low heat emission and long bulb life. However, the startup cost tends to be higher and some LEDs are not suitable for very deep tanks.

Now that we’ve given an overview of bulb types, let’s go over bulb combinations.


With most LED fixtures, it would be pointless to speak about choosing bulb combinations, since they are chosen for you. Many LED fixtures on the market today allow you to individually dim different parts of the color spectrum to create an unprecedented level of customization. In fact, if you are looking to purchase a fixture rather than just choose bulbs, this may be the best bet for you. If you are using LEDs to supplement your primary lighting, you will want to focus on blue strips/bulbs to take advantage of the wonderful fluorescence they produce.


There are several great bulb manufacturers whose bulbs can be mixed and matched to create a great looking tank. We have put together some reference charts below for the most popular T5 fluorescent bulb brands to help you get an idea for how you might mix-and-match yourself. We have focused on T5 fixtures, which are the most popular. If your light fixture has multiple plugs to simulate dawn/dusk, put actinics and blues all on one plug to create the best effect.

  • Giesemann T5 Bulb Combinations
  • Red Sea T5 Bulb Combinations
  • UV Lighting T5 Bulb Combinations
  • ATI T5 Bulb Combinations
  • AquaticLife T5 Bulb Combinations

Metal Halide and Supplemental Lighting

Most hobbyists choose a metal halide in the color they are looking for and then supplement with actinic or blue fluorescents/LEDs.

  • 10k reef top: 10k metal halide supplemented with pure actinic and blue plus.
  • 14k mid reef: 14k metal halide bulb supplemented with pure actinic, or blue and actinic
  • 20k deep reef: 20k metal halide supplemented with pure actinic

We hope this information is helpful in choosing lighting for your tank. These guidelines will help you wade through the many possible combinations you have to choose from. We are, of course, always happy to answer any questions you have about the choices before you.