What is PAR and How Much Do I Need?

What is PAR and How Much Do I Need?

PAR is a common term you will hear on a regular basis while reading about reef tank lighting.  If you’re new to this hobby and still learning the basics, you likely have many questions about PAR… What is it? Why does it matter for reef aquariums?  Why should you care about it?

What is PAR?

PAR is an acronym for Photosynthetic Available Radiation or Photosynthetic Active Radiation.  For the purpose of keeping an aquarium, PAR is the amount / intensity of light that is in the proper spectrum for corals to utilize.  On the other hand, lumens is the intensity of visual light to humans or how bright a light looks to humans. In other words, the difference between the two is simple: PAR is usable for corals, lumens is visible for humans.  Therefore, it’s important to keep in mind that humans can be terribly inept at measuring it!

Why Is PAR Important for Reef Tanks?

PAR levels are important for assessing the following: (1) adding new coral to a tank and (2) comparing light fixtures with one another.

When adding a new coral to a tank, it is important to replicate the same PAR levels that those corals had been accustomed to from their original tank. When purchasing or acquiring a new coral, you’ll want to know their current levels and find a location within your tank that closely match. If you would prefer to have the coral in a different location in your tank, start at a location that closely matches the previous levels. Then over time, gradually move it up or down in the water column until the preferred location is reached.

In today’s world, most mainstream light fixtures produce plenty of PAR. However, if you are considering a lesser known or unproven brand, reviewing PAR data can help ensure you are getting a light capable of growing the coral you wish to grow. When reviewing this data, light balance and distribution are generally more important than max PAR. A good quality light will produce uniform PAR numbers over the coverage area. On the other hand, a poor quality light may produce high values directly below the light but much lower numbers as you move farther away from the light source.

LED Light Spread
Pictured above: a representation of light spread produced by LEDs
T5 Light Spread
Pictured above: a representation of light spread produced by T5s

How Much PAR Do I Need for Coral?

So what do PAR numbers mean, exactly? Generally, low values are considered to be 100 or less, while high values are generally over 200. So how do you determine what your corals need? As a general rule of thumb, corals require the following PAR levels:

  • Soft Corals (zoanthids, palythoa, mushrooms and leathers): 50-150 PAR
  • LPS Corals: 50-150 PAR
  • Hard Corals (stony corals, small polyp stony): 200-500 PAR

Having said that, most corals are forgiving and can adapt to a wide range of different light levels when given proper time to acclimate. For example, euphyllia (hammers, frogspawn, torch, etc.) can handle PAR levels from 100 to 1000+ with adequate time to adjust.

How Important is it to a Successful Reef?

This is a highly debated question among reef aquarium hobbyists. There is no question PAR is important. In our opinion though, some folks put too much weight into it and sometimes overemphasize the values.

Corals are amazingly resilient creatures. They are capable of adapting to a wide range of light levels over time. In the wild, there are places where SPS corals live in full sunlight and exposed to the air at times of low tide.  Keep in mind this frequently occurs where the sun is very intense along the equator.  If someone believes their light can overpower the sun’s along the equator where corals are exposed without water, they are likely incorrect. In other words, you cannot give SPS or most other corals too much light, but it is possible to expose them too quickly.  Corals are very adaptable to light, they just need time to adjust to changes in intensities.

Chasing PAR values is not what most corals need. Rather, corals require careful observation and adjustments based on their individual needs and reactions. For instance, if a coral starts to lose color, you may want to try reducing the light intensity. This can be done by moving the coral deeper in the water column or out towards the edges of the tank where PAR is generally lower. On the other hand, if a coral starts turning brown, it may require more light. (Water quality may also be a culprit in that case as well.)

Additionally, many people purchase waterproof PAR meters. While these can help better understand the ranges in an aquarium, careful observation is still extremely important. Simply by watching your coral over time, you can learn how to better recognize their needs.

So there you have it!  PAR can provide useful insights and help you better understand the difference from one light to another. However, it is not the only factor to take into account. Constant observance of your corals is still paramount for learning how your corals react and thrive!

Have a question or need assistance with your ATI lighting? Click here to contact us, we’d love to hear from you!

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