Coral lighting has three linked variables: spectrum (the wavelengths supplied), PAR (the photosynthetically active photon flux reaching a coral), and photoperiod (how long the light is on, alongside a dark period). There is no single blue-white mix, PAR target, or daily schedule established for every coral. Measure conditions at the coral’s position, then adjust cautiously for the species and aquarium.
What is PAR?
PAR, or photosynthetically active radiation, describes photons in the 400–700 nm band used in photosynthesis. Aquarium PAR is typically reported in micromoles per square metre per second (µmol m⁻² s⁻¹). It is a measure of photon flux, not a complete description of which wavelengths make up that light.
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A NOAA technical-memo excerpt identifies the 400–700 nm range and emphasizes measuring underwater at coral depth rather than relying on a reading at the water surface. Immersion correction and sensor geometry affect readings, so use a submersible quantum sensor and follow its instructions: NOAA coral aquaculture technical memo 18.
Why lux, lumens, and fixture percentages are not substitutes
Lux and lumens weight light for human vision; watts describe energy, while a fixture’s percentage is a control setting. None alone tells you the PAR at a coral’s location. Color temperature also does not describe the actual spectral distribution well enough to replace a spectrum measurement or PAR reading.
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- One ClassicLED Marine light will support saltwater fish, live rock, soft coral, and LPS corals. For low light SPS corals, we suggest using two lights
- Available in multiple sizes and includes extendable brackets on both ends to accommodate both rimless and framed aquariums length 48 - 60 inch
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How much PAR do corals need?
No universal numeric PAR target for all marine aquarium corals is established by the sources cited here. Needs can vary with coral species, placement, spectrum, and acclimation. Treat any number as relevant only when it is tied to a particular coral and measured conditions—not as a target for an entire mixed reef.
PAR is spatial: light levels can differ between the surface, shaded areas, and different spots at the same depth. Map likely coral positions with the same sensor and placement method rather than using a surface value to characterize the whole tank. A study of Goniopora columna reports daily measurements with an Apogee MQ-510 underwater quantum meter; that is an example of a measurement tool, not a requirement to buy that model. Read the 2022 study.
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- Features 445nm and 460nm blue, 10,000K white, and RGB LEDs, a higher ratio of actinic blue spectrum LEDs balanced with full spectrum creates the ideal color combination for the saltwater environment
- Comes with the day+night controller to adjust the lighting spectrum, simulate a gradual sunrise and fading sunset through the gradual increase and decrease of light intensity
- One ClassicLED Marine light will support saltwater fish, live rock, soft coral, and LPS corals. For low light SPS corals, we suggest using two lights
- Available in multiple sizes and includes extendable brackets on both ends to accommodate both rimless and framed aquariums length 36 - 48 inch
- A glass or acrylic canopy is highly recommended to extend the life of the unit by preventing moisture from affecting it
A genus-by-genus PAR chart compiled from selected Seneye data is a secondary resource, not a gold-standard prescription. Do not let a general chart override measured conditions at the coral’s position or evidence specific to the species you keep.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsWhat spectrum is best for corals?
There is no proven best spectrum for every coral or reef aquarium. A coral pathology and management guide from the Institut océanographique de Monaco describes symbiotic corals as preferring higher irradiance in the 400–500 nm range and lower irradiance in the 650–700 nm range. This is husbandry guidance, not a complete fixture recipe or proof that every coral responds identically: Coral Pathology Identification and Management in Aquarium.
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- 2 Lighting Modes: Short press the M button repeatedly to switch between daytime and night modes. Hold the M button for 3 seconds to turn all lights off. Simulate natural sunrise and sunset to energize your lovely aquatic pets and give them a sound sleep
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What the species studies show—and do not show
An eight-week experiment on Goniopora columna tested white, yellow, red, green, blue, and purple LEDs. It reported favorable growth, survival, protein content, and protease activity under blue (440–470 nm) or purple (400–430 nm) light for at least six hours per day in the experiment’s conditions. Each group included 30 colonies across three experimental repetitions. The authors concluded that 400–470 nm could be a primary illumination range for efficient cultivation of this species. These results do not establish a narrow-band lighting recipe for mixed reefs or other corals. Study details and results.
In a separate study, the indexed abstract reports no significant main effect of spectrum on specific growth rate for Galaxea fascicularis in the tested comparison. That finding is another reason not to turn one species’ result into a universal blue-versus-white rule: Aquaculture study on irradiance and spectrum.
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- Comes with the dual-channel timer to adjust the lighting spectrum, simulate a gradual sunrise and fading sunset through the gradual increase and decrease of light intensity
- One ClassicLED Marine light will support saltwater fish, live rock, soft coral, and LPS corals. For low light SPS corals, we suggest using two lights
- Available in multiple sizes and includes extendable brackets on both ends to accommodate both rimless and framed aquariums length 30 - 36 inch
- A glass or acrylic canopy is highly recommended to extend the life of the unit by preventing moisture from affecting it
Choosing a spectrum-capable fixture
Compare fixtures on measured PAR distribution where corals will sit, spectral adjustability and coverage, dependable dimming and scheduling controls, and fit for tank dimensions and coral mix. Philips/Signify describes its CoralCare Gen2 as using two controllable channels and multiple blue wavelengths, including 415–490 nm, to balance coral appearance and fluorescence with growth goals. Those are manufacturer product statements, not an independent comparison or general husbandry rule: Philips CoralCare spectrum information.
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How long should reef lights be on?
Photoperiod should be considered together with intensity: a longer exposure is not automatically better, and the evidence here does not establish one schedule for every tank. Red Sea Chief Scientist Sharon Ram’s January 2020 guidance recommends roughly 12 hours of light and 12 hours of darkness, describes an inverse relationship between intensity and duration, and says moonlight should be very low or counted as part of the photoperiod. That is Red Sea’s recommendation, not a universal biological threshold. Read the Red Sea guidance.
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The Goniopora columna experiment compared six- and 12-hour daily exposures over eight weeks; its favorable blue or purple results for that coral do not settle schedules for other species, mixed reefs, or different light intensities.
Why provide darkness?
Darkness is part of the light cycle, not an opportunity to keep extending illumination with bright nighttime settings. Ram wrote: “Even the optimal amount of daily photosynthetic activity generates residual energy inside the coral that must be released, so they need a period of darkness, just as much as they need the light.”
A peer-reviewed study examined white LED artificial light at night in Red Sea corals. One treatment group received a reported 1–1.5 µmol quanta m⁻² s⁻¹ (35–40 lux); the study reports oxidative stress and photosynthetic impairment under its artificial-light-at-night conditions. This was an experimental exposure, not a recommended aquarium night-light level, and does not show that every brief, dim moonlight setting harms every coral: Study of artificial light at night in Red Sea corals.
How should you adjust aquarium lighting?
- Identify coral locations. Note where corals sit and which areas are shaded before changing the light schedule or output.
- Measure PAR underwater. Take readings at coral depth with a submersible quantum sensor. Map more than one likely placement and use consistent sensor positioning when comparing readings.
- Review spectrum and schedule together. Check the fixture’s spectral controls and daily timing. Preserve a regular dark period rather than treating a moonlight setting as free additional daylight.
- Change conditions cautiously. Avoid abrupt increases in intensity or exposure duration. Red Sea’s guidance identifies tissue retraction or paling as possible signs of photoinhibition; use such changes as a reason to reassess exposure rather than as a diagnosis on their own.
- Recheck at coral level. After an adjustment, measure again in the same positions and evaluate the corals over time. A change to fixture percentage alone does not reveal how much PAR reached the coral.
What should you look for in a reef light?
Choose based on the aquarium and its corals, not a claimed universal “coral setting.” Useful comparison criteria are:
- PAR coverage measured at the intended coral positions, including shaded or edge areas.
- Adjustable spectrum and coverage appropriate to the tank’s dimensions and coral mix.
- Reliable dimming and scheduling that can maintain a consistent dark period.
- Controls that make gradual changes and repeatable settings practical.
Manufacturer descriptions from Philips/Signify and Red Sea can explain their own products and recommendations, but the cited sources do not establish an independent comparative winner.
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