Reef lighting is the single most expensive part of a marine aquarium build and the one with the most variation in opinion across hobbyists. The good news is that the science has been settled for over a decade: corals need specific PAR (Photosynthetically Active Radiation) ranges, specific spectrum, and a stable photoperiod, and once those are dialed in they grow and color up reliably. This guide covers the target PAR for each coral category, the spectrum settings that drive growth and color, the photoperiod that mimics natural reefs, and the acclimation schedule that prevents the bleaching most beginners cause when they crank a new light to full power.
Why PAR matters more than watts or lumens
Lumens measure visible light intensity to human eyes. Watts measure electrical input. Neither tells you anything useful about coral photosynthesis. Corals use light in the 400 to 700 nanometer range (the same as plants, but with different absorption peaks), and that usable light is measured as PAR. A PAR meter held at coral height in your tank reads the actual usable intensity arriving at that coral.
Reef LEDs in 2026 are mostly tuned for PAR efficiency. A Radion XR15 G6 or AI Hydra 32HD running at 50 percent power delivers different lumens than a 50 percent power Ecotech Mover, but the PAR readings are similar because both fixtures are calibrated to coral spectrum.
PAR targets by coral type
Soft corals (zoanthids, mushrooms, leathers, xenia, GSP)
Target: 50 to 150 PAR
Soft corals tolerate a wide range and grow well in shaded or low-light areas of the tank. Mushrooms and zoanthids on the sand bed in a tank with reef-grade lighting typically receive 80 to 120 PAR, which is ideal. Leathers and tree corals tolerate up to 200 PAR but actually grow faster at 100 to 150. GSP (green star polyps) grows aggressively at 150+ PAR and can be controlled by placing it on a frag plug in lower light.
LPS corals (hammers, frogspawn, torches, acans, chalices, brains)
Target: 100 to 250 PAR
LPS sits in the middle of the reef. Most LPS corals do best on the rockwork at mid-tank height where PAR reads 120 to 200. Hammers and torches will tolerate 250 PAR with the right flow. Acans and chalices prefer the lower end, 80 to 150 PAR, and color up better in subdued light. Brains and platygyras want 100 to 150 PAR with low flow.
SPS corals (acropora, montipora, stylophora, pocillopora, seriatopora)
Target: 200 to 400 PAR
SPS is the high-light category. Acropora wants 250 to 400 PAR with high flow. Montipora capricornis tolerates 150 to 300 PAR. Encrusting montiporas, stylophoras, and pocilloporas thrive at 200 to 300 PAR. The high end (350+ PAR) is reserved for the top of the tank near the water surface.
Anemones (bubble tips, carpets, sebae)
Target: 150 to 300 PAR
Bubble tip anemones (BTAs) prefer 200 to 300 PAR with strong flow. Carpet anemones tolerate similar ranges but are more sensitive to flow changes. New anemones should be acclimated over 2 to 3 weeks before reaching their target PAR.
Spectrum settings
A modern reef LED has 6 to 14 separate channels, each producing a specific wavelength. The standard channels are:
- Royal blue (450 nm): peak photosynthesis, drives growth and pigment fluorescence
- Blue (470 nm): secondary photosynthesis, blue color
- Cyan (490 nm): supports photosynthesis, helps render greens accurately
- Green (520 nm): viewing only, low photosynthesis impact
- Cool white (10K to 14K): full spectrum, supports photosynthesis and renders true colors
- Warm white (6.5K to 8K): needed in small amounts for red and orange visibility
- Red (660 nm): small amounts boost red coloration in some corals
- UV (385 to 405 nm): triggers fluorescent proteins for pop colors
- Violet (415 nm): similar to UV, drives fluorescence
A reasonable starting spectrum on a Radion or AI Hydra:
- Royal blue: 80 to 100 percent
- Blue: 70 to 90 percent
- Cyan: 30 to 50 percent
- Green: 10 to 30 percent
- Cool white: 30 to 60 percent
- Warm white: 5 to 20 percent
- Red: 10 to 30 percent
- UV: 30 to 60 percent
- Violet: 40 to 70 percent
The exact numbers depend on the brand and model. Most manufacturers publish reef-ready presets (AB+ for Radion, Black Box settings for AI) that work as starting points.
Photoperiod and ramp schedule
A reef cycle should run 8 to 10 hours daily with a graduated ramp at the start and end.
A working schedule:
- 09:00: lights at 0 percent, start blue ramp
- 10:00: blues at 50 percent
- 11:00: blues at 100 percent, whites start to ramp
- 12:00 to 18:00: full peak, all channels at target
- 18:00 to 19:00: whites ramp down
- 19:00 to 20:00: blues ramp down
- 20:00: blue-only mode at 10 to 20 percent for viewing
- 22:00: lights off
The ramp prevents abrupt intensity changes that stress fish and corals. The blue-only viewing period is optional and useful for evening fluorescence displays.
The acclimation schedule for a new tank or new light
A new light or a new coral cannot tolerate full PAR immediately. Corals adjust their zooxanthellae density over 2 to 6 weeks based on light intensity. Hitting them with full PAR before they have adapted causes bleaching.
The acclimation schedule for a new LED on an existing tank with corals:
- Week 1: 30 percent of target intensity
- Week 2: 50 percent
- Week 3: 70 percent
- Week 4: 85 percent
- Week 5: 100 percent
The acclimation schedule for a new coral going into an established tank:
- Week 1: place the coral on the sand in the lowest-PAR zone
- Week 2: move the coral halfway to its final position
- Week 3: move the coral to its final position
- Week 4 onward: monitor for color change and pull back if bleaching starts
Signs of light stress: tissue paling, mucus production, polyp retraction lasting longer than 24 hours, brown algae bloom on the coral skeleton (a sign of zooxanthellae expulsion).
How to measure PAR without buying a meter
Most reef-keepers do not own a PAR meter. Three alternatives:
- Borrow from a local club: every reef club has at least one Apogee meter circulating
- Use manufacturer charts: Radion, AI, and Ecotech publish PAR-vs-distance charts for each fixture
- Coral behavior: pale tips, brown corals that should be green, polyps pulled in for days. These are signals to reduce intensity. Conversely, slow growth and dark coloration in SPS suggest too little light
For a complete reef setup, see our coral care guide for soft, LPS, and SPS and the reef tank starter species guide. The /methodology page covers our reef trial protocol.
Frequently asked questions
What PAR level do SPS corals need?+
Acropora and other SPS corals want 200 to 400 PAR at their position in the tank. Encrusting montiporas and milleporas tolerate 150 to 250 PAR. Place SPS within 6 to 10 inches of the water surface in most setups, where PAR readings hit the target range with a quality reef LED.
How long should reef lights run per day?+
Eight to ten hours total, with a 2 hour ramp up, 6 hours at peak, and 2 hours ramp down. The ramp protects coral from instant high-intensity exposure and mimics the natural light cycle. Most reef LEDs include built-in ramp scheduling in their app.
What kelvin temperature is best for reef corals?+
Twelve thousand to twenty thousand kelvin is the standard reef range, with most aquarists running 14K to 18K. Higher kelvin pulls more blue spectrum, which fluoresces coral pigments and produces the colors most reefers want. Pure white light at 6500K does not grow reef corals well.
Do I need a PAR meter for a reef tank?+
Yes if you keep SPS or have multiple light points across a larger tank. An Apogee MQ-510 underwater PAR meter ($530) or a rented PAR meter from your local fish store reveals dead zones and high-intensity spots that are not visible by eye. Most reefers borrow one rather than buy.
Should I run blue-only mode for color or full spectrum for growth?+
Run full spectrum during the 6 hour peak period for photosynthesis, with extra blue at the start and end of the cycle for viewing and fluorescence. Pure blue does not grow corals well long term, photosynthesis needs the white and red wavelengths too.
Priya Sharma
Priya Sharma writes for The Tested Hub.