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How Long to Run Reef Aquarium Lights
Last updated on November 17th, 2023
How Long Should I Run my Reef Tank Lights?
One of the most common questions in aquarium lighting is "How Long Should I Run my Reef Tank Lights?". The best lighting duration, or "on time", depends on the type of light you're using as well as your tank and the types of corals you're growing. If you're growing SPS (Small Polyp Stony) or LPS (Large Polyp Stony) corals, you will need to utilize higher intensity lighting, where soft corals can get by with low intensity lighting. However, you may be able to grow some of these coral by running lighting that falls between these if you run the lights longer! Let's take a look below.
High PAR / High Intensity Lighting
High intensity lighting generally includes Metal Halide (MH), T5 Fixtures with 6 or more bulbs, and some high end LED fixtures such as Ecotech Radion or Orphek LED Lights. Though these are the lights generally referred to as "high intensity", if you have a shallow aquarium, such as a breeder or "low boy" tank, lower intensity light fixtures may provide "high intensity" PAR values.
So what is considered High Intensity PAR? In terms of How Long to Run Reef Aquarium Lights, or Photoperiod, high par seems to be 250 - 350 PAR. This is roughly what you will be looking at with the high intensity lighting mentioned above.
With a PAR of 250 and above, a good starting point is to keep the lights on for 9 hours. This is only including the "full on" time period. If you ramp your lights up, or turn on individual fixtures or bulbs at a time, do not include the ramp up time in this 9 hours.
You may have noticed I said "starting point". Some coral, such as acropora, require more light. If your coral is not happy with this amount of lighting, you will need to increase or decrease the photoperiod based on what you see. If your coral is bleaching, you may have too much light and need to run the lights for a couple hours less, or decrease the PAR. If the coral is losing color or becoming "dull", you may need more light, and may consider running the lights for a longer time.
This may not be a perfect number, but that is because every reef tank is different. Different dimension, coral types, coral location, spectrum, and even hanging heights. Because of this, you will have to look for what works best for the majority of your coral and then perhaps move unhappy coral to a higher or lower PAR location in your tank based on its needs.
If your coral is bleaching, or you are trying to decide which light fixture is best, you may want to check out the following articles:
"Low" PAR / Standard Intensity Lighting
For low PAR lighting, or deeper aquariums, you will need to have a longer light period. If you prefer to have a longer lighting period, many high end LED fixtures, such as the Ecotech Radion XR30w Pro or Orphek Atlantik light fixtures, have the ability to decrease the intensity to allow for a desired photo period, or "on time". For low PAR systems, it is ideal to start with a 12 hour photo period and work up or down from there similar to that of the High PAR lighting.
This low PAR lighting is anything under 250 PAR. This may include LED lighting that has the intensity set low, a small number of T5 bulbs, or lower quality LED fixtures. Personally, I do not recommend trying to keep high end coral under low par. Even with longer photo periods, many coral such as SPS will not do well.
Dark Period
Like most living creatures, coral and fish need a dark period to rest. This lights out time allows coral to expel toxics such as the CO2 generated from the photosynthesis process. Though there is not a specified window, I would recommend at least 12 hours as this would also enforce the ideal "on times" mentioned in this article.
Optimal Combination
If you can adjust the intensity of light for your light fixture, you can utilize a combination of high and low intensity periods, giving you the best viewing and growing times. Aiming for roughly 9 hours of high intensity light would be sufficient for most corals, but is a short window of time for enjoying your reef tank. Additionally, a sudden change from no light to full intensity can cause some amount of shock to the corals. So what's the solution? You can ramp the lights up for an hour and a half before the main lighting time, and ramp down over an hour and a half to give you a full 12 hours to look at your tank! You can then adjust the ramping time and "on time" based on your corals' needs.
Conclusion
Essentially, the ideal time to have your lights on full is between 9 and 12 hours. Providing ramp up and ramp down time if possible. This gives the coral enough time (roughly 9 hours) to grow and reward from the photosynthesis. The low intensity lighting time, or ramping time, gives you more time to enjoy your reef tank! Giving you the best of both worlds.
More Information about Lighting your Reef Tank
For more information about lighting your reef aquarium and coral lighting needs, check out the A Complete Guide to Saltwater Aquarium Lighting.
Related Reading:
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About the Author
John Krenzer
John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.
Today, John maintains an over 300 gallon reef tank system, consisting of a 120g reef and a 210g reef. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.
John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.
If you would like to request an article, tank tour article, or to collaborate, let me know via the Contact Me Page!
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