RecifAtHome guide
Light is the main energy source for corals: their symbiotic algae, zooxanthellae, produce most of the energy they need through photosynthesis. Getting your lighting right promotes both growth and colour.
In short
- The light available to corals is measured as PAR (µmol/m²/s).
- Soft corals 50 to 150, LPS 75 to 200, SPS 200 to 400 µmol/m²/s.
- 8 to 10 hours at full intensity, with gradual ramp-up and ramp-down.
- Every new light or new coral must be acclimated gradually.
What is PAR?
PAR (photosynthetically active radiation) measures the amount of light available to zooxanthellae, in micromoles of photons per square metre per second (µmol/m²/s). Unlike watts or lumens, it tells you how much light a coral receives at its position in the tank. A PAR meter lets you map your tank in a few minutes.
How much light do different corals need?
| Animals | Recommended PAR (µmol/m²/s) |
|---|---|
| Soft corals, Zoanthus, Ricordea, Discosoma | 50 to 150 |
| LPS (Euphyllia, Acanthastrea, Favia…) | 75 to 200 |
| SPS (Montipora, Pocillopora, Acropora) | 200 to 400 |
| Giant clams derasa and squamosa | 150 to 200 |
| Giant clams maxima and crocea | 250 to 300 and above |
These ranges are guidelines: a coral accustomed to lower light must be acclimated gradually to higher intensity.
Spectrum
Corals mainly use blue (420 to 470 nm) and violet light, plus some red. Reef lighting is therefore predominantly blue, with white light for colour rendering. A very blue spectrum enhances fluorescence; more white gives a more natural appearance. UV and violet (400 to 420 nm) bring out fluorescent colours.
Photoperiod
Programme 8 to 10 hours at full intensity, with a one- to two-hour ramp-up and ramp-down. Beyond 12 hours of total lighting, algae benefit without any gain for the corals.
Light acclimation without bleaching
- New lighting: start at 40 to 50 % of the target intensity, then increase by 5 to 10 % per week over 4 to 6 weeks.
- New coral: place it lower than its intended final position, then move it up over two to three weeks.
- Too much light: the coral pales or bleaches from the top, polyps stay retracted.
- Too little light: the coral browns, polyps stretch, growth slows.
Choosing your lighting
- LED spotlight fixtures (AI Hydra, EcoTech Radion, Kessil) create shimmer and can be combined to cover the tank.
- LED bars and panels (Red Sea ReefLED, Maxspect, Philips Coral Care) distribute light evenly and reduce shadowing.
- As a rule, allow one spotlight fixture per 40 to 60 cm of tank length, depending on the model and water depth.
Frequently asked questions
What PAR for SPS corals?
Between 200 and 400 µmol/m²/s depending on the species and placement. Montipora do well at the lower end.
How many hours of light for a reef tank?
8 to 10 hours at full intensity with gradual ramps, so 10 to 12 hours in total.
Why are my corals turning brown?
Often a lack of light or excess nutrients. Measure PAR, nitrate and phosphate before changing your lighting.
Do I need a PAR meter?
It is not essential, but it is the most reliable tool for placing demanding corals and setting up a new light.
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Guide written by the RecifAtHome team, coral aquaculture in Roche-lez-Beaupré (France) since 2010. Updated: October 2026.