Coral Lighting & PAR Guide

Reef Aquarium Lighting

Why Coral Lighting Matters

Light is one of the major environmental factors that influences photosynthetic coral health, coloration and growth.

Many reef-building corals contain photosynthetic dinoflagellates commonly called zooxanthellae. Through photosynthesis, these symbiotic organisms contribute energy that helps support the coral.

Providing appropriate reef lighting therefore involves more than making an aquarium look bright. You need to consider intensity, spectrum, photoperiod, placement and stability.

Different corals can thrive under very different lighting conditions. Even two colonies of the same general coral type may respond differently depending on what lighting they were previously accustomed to.

The key idea: PAR ranges are useful starting points—not universal guarantees. Coral species, previous lighting conditions, spectrum, water clarity, aquarium depth and other factors all influence how a coral responds.

Understanding PAR

What Is PAR in a Reef Tank?

PAR is one of the most useful measurements reef keepers use when evaluating coral lighting.

01

Photosynthetically Active Radiation

PAR stands for Photosynthetically Active Radiation and refers to light within approximately the 400–700 nanometer wavelength range used in photosynthesis.

A PAR meter measures photosynthetic photon flux density, typically expressed as micromoles of photons per square meter per second (µmol/m²/s).

02

Why PAR Is Useful

Human eyes are poor tools for judging how much usable light reaches a coral. Two locations that appear similarly bright can have very different PAR levels.

Measuring PAR helps you map the aquarium and make more informed decisions about coral placement.

General Starting Points

Coral PAR Ranges

These broad ranges can help with initial placement, but the needs of the individual coral should always take priority.

50–100

Lower Light

Often suitable for lower-light corals and for carefully beginning light acclimation.

100–200

Moderate Light

A common range for many soft corals and numerous LPS corals.

200–350

Higher Light

Common territory for many light-demanding corals, including many SPS.

350+

Very High Light

Appropriate for some high-light corals only when their needs and previous lighting conditions support it.

Don't chase a number: A coral doing well at 180 PAR does not automatically need to be moved to 250 PAR simply because a chart lists a higher range. Observe the coral and prioritize stability over constantly adjusting placement.

Quick Reference

Typical PAR Starting Ranges by Coral Group

Coral Group	General Starting Range	Typical Light Level	Important Consideration
Soft Corals	50–150 PAR	Low to Moderate	Many soft corals are adaptable, but individual species vary.
Zoanthids	75–200 PAR	Low to Moderate	Many zoanthids adapt to a broad range when changes are gradual.
LPS Corals	75–200 PAR	Low to Moderate	Euphyllia and other LPS often do well under moderate lighting, though requirements vary.
Goniopora	75–200 PAR	Low to Moderate	Species and individual colonies can respond differently.
SPS Corals	200–350+ PAR	Moderate to High	Many SPS benefit from stronger lighting, but stability and acclimation remain important.
Acropora	200–400+ PAR	Moderate to High	Exact requirements vary substantially by colony and previous lighting conditions.

Lighting by Coral Type

Soft, LPS & SPS Coral Lighting

Coral categories provide useful starting points, but individual species and colonies can have different requirements.

Often Lower to Moderate Light

Soft Corals

Many soft corals tolerate a relatively broad lighting range, making them popular choices for newer reef keepers.

Shop Soft Corals →

Often Moderate Light

LPS Corals

Many LPS corals perform well under moderate lighting, though placement should be adjusted for the individual species.

Shop LPS Corals →

Often Moderate to High Light

SPS Corals

Many SPS corals are associated with higher PAR, but strong lighting should still be introduced gradually.

Shop SPS Corals →

More Than Intensity

Coral Lighting Spectrum

PAR tells you how much photosynthetically active light is present, but it does not tell the entire story about the spectral composition of that light.

Blue & Violet Light

Modern reef lighting commonly emphasizes blue and violet wavelengths. These wavelengths are important to photosynthetic organisms associated with corals and also help reveal fluorescent pigments.

A blue appearance does not automatically mean PAR is low. Powerful reef LEDs can produce substantial PAR even when the aquarium appears visually blue.

White & Broad Spectrum Light

White channels can improve visual color rendering and contribute additional wavelengths and PAR.

There is no universal channel percentage that works for every reef light. Fixture design, mounting height, aquarium dimensions and coral placement all influence the result.

Avoid copying percentages blindly. A setting such as “70% blue and 20% white” can produce very different PAR on different fixtures. Use manufacturer guidance, coral response and PAR measurements when available.

Daily Lighting Schedule

How Long Should Reef Tank Lights Be On?

Intensity and duration work together, so photoperiod should be considered alongside PAR.

01

Ramp Up

Many programmable reef lights gradually increase intensity instead of switching instantly from darkness to peak output.

02

Peak Period

The aquarium can then remain near its primary daytime intensity for several hours depending on the system and lighting strategy.

03

Ramp Down

A gradual decrease can provide a natural-looking transition into the evening while maintaining a consistent daily schedule.

Common starting point: Many reef aquariums use roughly an 8–12 hour overall lighting window, often with a shorter period at peak intensity. The ideal schedule depends on the aquarium, fixture, intensity and livestock.

Coral Placement

PAR Changes Throughout the Aquarium

Moving a coral only a few inches can significantly change the amount of light it receives.

Higher Doesn't Always Mean Better

The top of the aquascape often receives more light, but the brightest location is not automatically the best location for every coral.

Lower-light LPS and soft corals may perform better farther from the fixture or in partially shaded areas.

Shadows & Hot Spots Matter

Rockwork, coral colonies, braces and the geometry of the light can create shadows and high-intensity areas.

Mapping several locations with a PAR meter provides much more useful information than taking only one measurement in the center of the tank.

Prevent Light Shock

How to Light Acclimate New Corals

A coral may need time to adjust when your aquarium lighting differs significantly from its previous environment.

1

Start Conservatively

When appropriate, begin the coral under somewhat lower intensity rather than immediately exposing it to the strongest part of your lighting system.

2

Increase Gradually

Gradually move the coral toward its intended PAR or use your reef light's acclimation feature to increase intensity over time.

3

Observe the Coral

Watch tissue, coloration and polyp extension rather than increasing light simply because a predetermined schedule says it is time.

Adding a new coral? Lighting is only one part of the process. Read our complete coral acclimation guide for inspection, dipping, placement and the first 24–72 hours.

Troubleshooting

Signs Your Coral Lighting May Need Attention

Lighting problems can resemble issues caused by water chemistry, flow, pests and other stressors, so avoid diagnosing a coral from one symptom alone.

Paling or Bleaching Rapid paling after an increase in intensity can be a warning that a coral is receiving more light than it is accustomed to.

Coral Remains Retracted Persistent retraction can have many causes, including inappropriate lighting, flow, chemistry or irritation.

Stretching Toward Light Some corals may extend or change their growth form when seeking more light, although behavior varies by species.

Unexpected Color Changes Coral coloration can respond to changes in light intensity and spectrum, but nutrients, health and other environmental factors also matter.

Before changing your lights: Verify your reef tank water parameters . A coral that appears unhappy may be responding to chemistry, flow, pests or instability rather than lighting alone.

Avoid These Problems

Common Reef Lighting Mistakes

Changing Intensity Too Quickly

Large sudden increases can stress corals that were previously accustomed to lower light.

Chasing Someone Else's Settings

Another aquarium's channel percentages may not produce the same spectrum or PAR in your aquarium.

Assuming Every SPS Needs Maximum PAR

SPS requirements vary. More light is not automatically better once a coral is already receiving an appropriate amount.

Ignoring Shading as Corals Grow

Mature colonies can shade lower branches and neighboring corals, changing PAR distribution over time.

Adjusting Too Many Variables at Once

Changing lighting, flow, nutrients and chemistry simultaneously makes it difficult to determine what actually affected the coral.

Relying Only on Appearance

Your eyes adapt to brightness. A PAR meter can reveal differences that are difficult to judge visually.

Frequently Asked Questions

Coral Lighting & PAR FAQ

What PAR is best for corals?

There is no single PAR level that is best for every coral. Many lower-light corals can thrive around 50–150 PAR, many LPS around 75–200 PAR, and many SPS around 200–350 PAR or higher. Individual coral requirements and previous lighting conditions should guide placement.

What PAR do LPS corals need?

Many LPS corals can do well within approximately 75–200 PAR, but requirements vary by species and colony. Some prefer the lower end while others tolerate or benefit from higher intensity.

What PAR do SPS corals need?

Many SPS corals are kept around 200–350 PAR, while some Acropora and other high-light corals may thrive at higher levels. Strong lighting should still be introduced gradually.

How much PAR do soft corals need?

Many soft corals can thrive under roughly 50–150 PAR, although species differ and some adapt to stronger lighting.

How many hours should reef tank lights be on?

Many reef aquariums use an overall lighting window of roughly 8–12 hours, often including ramp-up and ramp-down periods with a shorter period at peak intensity. The appropriate schedule depends on the fixture, intensity and aquarium.

Can corals get too much light?

Yes. Excessive intensity or a rapid increase in light can stress corals and may contribute to paling or bleaching. Gradual acclimation is particularly important after significant lighting changes.

Do I need a PAR meter for a reef tank?

A PAR meter is not required to own a reef aquarium, but it can be a valuable tool for understanding light distribution and making more informed coral-placement decisions.

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Build Your Reef Knowledge

Lighting works together with water chemistry, acclimation, flow and coral husbandry.

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