January 23, 2022

Saltwater Light Levels

Light Levels in The Saltwater Tank

Note: To learn more about how light is measured, please click here for an explanation of PAR, PPF, and PPFD as well as DLI.


Light Levels in The Saltwater Tank

Our LED fixtures have a horticultural, commercial and industrial pedigree which is why they put out extremely high levels of light. The purpose of this article is to help saltwater aquarists select the optimum light level for their aquarium.

When you order fixtures from Build My LED you’ll see there is a lighting calculation tool built into the ordering process that allows you to enter your aquarium size, preferred light fixture length, and your desired light level. You know the size of your aquarium and you probably have a fixture length in mind. But many customers are unsure about light levels — especially people new to the hobby. Even experienced hobbyists rarely have the equipment needed to measure light accurately. Hence, it can be a challenge for even experienced aquarists to accurately assess the required light levels.

A General Guideline

Many corals can live in relatively low light but need higher light to thrive — some corals (stony or soft) confound experts because they will sometimes grow well when the light is a lot lower than recommended. The bottom line is that growing corals successfully is part science and part art — successful reef keepers know they will have to tweak and change their lighting configurations along with their feeding schedules, photoperiods, and other variables.

Our “standard” light levels

If you put five aquarists in a room and ask them to each define low light, medium light, and high light, you would no doubt get five completely different answers.

To help bring some sanity to the process of ordering light fixtures for your tank we’ve defined four “standard” saltwater light levels we believe are reasonably accurate definitions of what most saltwater aquarists think of when they talk about different light levels — and what they use on their tanks. Because freshwater tanks tend to use lower light levels we have created a separate set of definitions for freshwater use.

Saltwater light levels

Ultra-High Light is defined as the light level that should only be used by advanced aquarists and researchers seeking to maximize coral coloration through elevated chromoprotein levels. Ultra-high light will usually require the use of multiple fixtures, and users should have experience in maintaining a reef aquarium under high PAR levels. Depending on the light levels the corals were previously exposed to, users should slowly acclimate their tank to this light level by using a manual dimmer or a controller.

High Light is defined as the light level you will need to successfully grow hard corals, including SPS. This will likely require the use of multiple fixtures. Depending on the light levels the corals were previously exposed to, users should slowly acclimate their tank to this light level by using a manual dimmer or a controller.

Medium Light is defined as the level that is most often used to successfully keep soft corals and LPS in your aquarium. In the event, only one fixture is required and you want to add a supplemental fixture (Pure UV, Purple Wave or Super Actinic Reef), the use of a manual dimmer or controller is recommended to lower the total light level.

Viewing Light is used by those who don’t intend to grow coral but want an illuminated tank where the colors on fish will stand out.

IMPORTANT NOTE: The fixture calculator is designed to give you a recommendation on the number and length of fixtures needed to achieve a specified light requirement in the tank you select. Due to rounding, the calculator may return the same recommendation for multiple light levels. This is not an error.

Hopefully, these guidelines will be useful but we realize there is a huge amount of information to digest when it comes to setting up your first tank. If you are just starting out, we recommend joining one of the many forums where other hobbyists share their knowledge and where there are often excellent articles and detailed instructions on a wide range of topics. For reef tanks or for those considering adding corals to a fish tank we recommend: Reef Central

What happens once I select a light level?

If all that is needed is Viewing Light then a dimmer is probably an important accessory for your lighting system. But, after you purchase your fixtures, you will need to find a “sweet spot” where your light is balanced and the corals in your aquarium are receiving the appropriate amount of light.

All aquariums are different — and “tweaking” light levels is part of the art of managing and maintaining a great reef tank!

Keep in mind that the light level in your aquarium can be regulated in three ways once you purchase the fixture you want:

  1. You can regulate the distance between the fixture and the water surface.
  2. You can alter the photoperiod (length of time during the day during which the light is on).
  3. You can use a dimmer.

Many saltwater enthusiasts use a controller to regulate light (our fixtures are compatible with the Apex, Reef Keeper Lite Reef Angel controllers) and a controller will be helpful if you find that you need to reduce the amount of light in your tank.

A note on the lighting calculator

When using the light calculator to order and (depending both on the size of your tank and your preferred fixture length) you may find that the same number of fixtures are recommended for different light categories (i.e. High Light and Medium Light). This is not an error — it typically occurs when a single fixture provides high light levels in the aquarium you selected. If this happens, we recommend a dimmer to adjust the light down to your required levels (i.e. Viewing Light or Medium Light). It is our goal to make sure you get the right amount of light — we truly don’t want to sell you extra fixtures if you don’t need them and, if you order a fixture and find you don’t need it (provided it is not a custom-built spectrum), send it back for a complete refund of the product price.

2 thoughts on “Saltwater Light Levels

  1. Hello,
    I have a 75 watts led light from build my led with wired control. How do I know at what percentage should I set it for anemones and corals?
    Eight know it is at 50 percent but one of my anemones don’t like it, I don’t if it is too night, I have a 72 gallons reef tank, and don’t know how to use the lighting.
    Please help me figure it out.
    Thank you very much

  2. Hi, Brad Hawkins here!

    I’ve come across one of your lights, it might be an older model due to the summer is different from what you use now. I have 48” with 8 red lights, 12 blue and the rest white. Angle I can’t tell. Everything works like a champ. Just curious if you sell just the dimmers(this one looks like it’s been chewed on by a dog) and a rough estimate on the price for one of these new? Please! I look forward to hearing from you.


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