Reef corals do not all need the same amount of light. As starting points, Bulk Reef Supply (BRS) suggests 75–150 PAR for soft corals, 150–250 PAR for large-polyp stony (LPS) corals, and 250–350+ PAR for small-polyp stony (SPS) corals. These broad ranges are not species-specific guarantees: the right placement also depends on the coral, light spectrum, photoperiod, tank layout and how gradually light is introduced.
To decide where a coral should go, measure PAR at its intended location rather than judging by brightness or fixture wattage. Then match that reading to the coral’s needs and watch its response.
What does PAR mean in a reef tank?
PAR means photosynthetically active radiation: the intensity of light available for photosynthesis. Corals’ symbiotic zooxanthellae use light to produce energy. Too little intensity can contribute to weak color and slow growth; too much can stress or bleach corals. BRS explains the basics in its coral lighting and PAR guide.
PAR describes intensity, not spectrum. Two fixtures can produce the same PAR reading while delivering different spectral output, so a matching number alone does not establish that their light quality is equivalent.
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What PAR should my corals get?
Use group-level ranges as a first placement guide, not as hard biological limits. Coral species and the light schedule matter, and published guides do not use exactly the same categories or targets.
| Coral group | Starting PAR range | Context |
|---|---|---|
| Soft corals | 75–150 PAR | BRS guidance; publication date not stated on the retrieved page. |
| LPS corals | 150–250 PAR | BRS guidance; it cautions that some LPS do better at lower levels. Publication date not stated on the retrieved page. |
| Common LPS corals | 75–150 PAR | EcoTech Marine’s 2020 Radion G5 guide labels this “medium” light and specifies an eight-hour peak photoperiod. |
| SPS corals | 250–350+ PAR | BRS guidance; publication date not stated on the retrieved page. |
| Common SPS corals | 225–300 PAR | EcoTech Marine’s 2020 Radion G5 guide labels this “high” light and specifies an eight-hour peak photoperiod. |
The differing LPS and SPS ranges are not necessarily a direct contradiction. The guides use different categories, fixture contexts and targets. Keep the recommendation’s source and photoperiod context in view, and look up the needs of the particular coral you are keeping.
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How do I know where to place corals in my tank?
Light varies throughout an aquarium. Water depth, fixture mounting height, rockwork and water clarity all affect the PAR reaching a coral. A fixture’s wattage or how bright it looks to you cannot show the intensity at a specific spot.
Map the light before placing corals
- Measure PAR at several levels: the sandbed, halfway up the rockwork and near the top.
- Take readings at the actual spots where you plan to place corals, since rockwork and other obstructions can change local light.
- Use a meter suited to the typical reef-light spectrum where possible. BRS notes that a sensor not designed for reef lighting may give different readings.
- Because water movement can make readings fluctuate, record an average rather than relying on one momentary reading.
A reef-spectrum-capable meter gives you a more useful map than fixture specifications alone. In its PAR-measurement walkthrough, BRS uses an Apogee MQ-510 underwater PAR meter and suggests borrowing or renting a meter as alternatives to buying one.
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Match coral needs to the measured spots
Place lower-light corals in dimmer areas and corals that need more light in brighter zones, using the range for the individual coral as your guide. For example, an EcoTech-hosted World Wide Corals case study places shallow-water Acropora centrally in the area with the most PAR. The facility reported 250–275 PAR on its SPS run and 80–140 PAR for LPS and deep-water corals in another trough. Those are observations from its aquaculture setup, not universal targets for home aquariums. See the EcoTech-hosted World Wide Corals lighting case study.
How long should reef lights stay on, and how should I acclimate corals?
BRS suggests a one-hour ramp-up, eight hours at steady intensity and a one-hour ramp-down as a starting schedule. That is source-specific advice, not a mandatory schedule for every reef. BRS also recommends beginning at somewhat lower intensity because a large jump in light can bleach corals.
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When installing new lighting, EcoTech Marine’s 2020 Radion G5 guide recommends using acclimation mode to increase output gradually. Apply gradual changes after a lighting or intensity change rather than exposing corals to a sudden increase; the guides do not establish a universal acclimation rate.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do I need a PAR meter?
A PAR meter is useful when you need to know the intensity at coral locations, particularly when mapping an unfamiliar tank or adjusting placement. It makes the most direct comparison between a coral’s target range and the light in a particular spot. If buying a meter is not practical, BRS suggests borrowing or renting one.
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Measurements still need context: use a reef-appropriate sensor if possible, average readings that fluctuate with water movement, and remember that PAR does not describe spectrum. A meter reading is a placement aid, not a complete assessment of light quality or a guarantee of how an individual coral will respond.
What should I compare when choosing reef lighting?
Choose a light for the area and corals it must serve, not its wattage in isolation. BRS’s LED aquarium lighting buying guide emphasizes output, spread and controls. Compare:
- Coverage: whether light reaches the whole tank footprint and intended coral locations.
- Intensity: whether the fixture can provide suitable PAR where your corals will sit.
- Spectrum: whether it offers reef-appropriate spectral output; PAR alone cannot establish this.
- Control and acclimation: whether output can be adjusted gradually.
- Shadowing: whether directional LEDs or rockwork leave areas with less light.
Fixture count depends on tank size and coral goals, so assess coverage across your own layout rather than inferring it from wattage alone.
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