Almost no manufacturer publishes PAR. Here is what the measurement actually means, why a single figure misleads, and our full measured grids.
Ask what PAR a reef light produces and you will usually get one number. It is almost always the brightest point, directly under the fixture, at the height that flatters it most. That number tells you very little about whether the corals in the corners of your tank will thrive.
We have started publishing our full measurement grids: every reading, not the flattering one. This is what those numbers mean and how to read them.
What PAR actually measures
PAR stands for Photosynthetically Active Radiation: the band of light between 400 and 700 nanometres that drives photosynthesis. It is the light your corals can use, which is not the same thing as how bright the tank looks to you.
PPFD — Photosynthetic Photon Flux Density — is the measurement of how much of that band arrives somewhere, counted in micromoles of photons per square metre per second. Think of it as photon rainfall. People use "PAR" and "PPFD" interchangeably; strictly, PAR is the range being measured and PPFD is the number you get. Even a PAR meter reports PPFD.
The critical property: PPFD is a point measurement. A light is not a point. That single fact is why one number can mislead so badly.
Why only one number isn't enough
Here is our Natura iCon MAX, measured on a 6 × 12 grid at five distances from the fixture, water depth 55 cm (22 in).
At 15 cm the peak is 1820. It is a real reading and a genuinely large number. It is also close to useless on its own, because only 32 of the 72 measured points register any light at all. That is an intense, narrow core with dark ground either side of it.
Move the same fixture to 60 cm and the peak falls to 515, but now every one of the 72 points is lit, and the grid averages 324. Less intensity, vastly more usable coverage.
| Distance from light | Peak PAR | Centre average | Grid average | Points lit |
|---|---|---|---|---|
| 15 cm 6 in | 1820 | 1681 | 849 | 32 / 72 |
| 30 cm 12 in | 966 | 897 | 372 | 68 / 72 |
| 60 cm 24 in | 515 | 470 | 324 | 72 / 72 |
| 90 cm 35 in | 354 | 208 | 230 | 72 / 72 |
| 120 cm 47 in | 220 | 119 | 148 | 72 / 72 |
Orphek Natura iCon MAX, measured PAR (PPFD) in µmol photons m⁻² s⁻¹.
What a single OR4 bar looks like by comparison
LED bars behave differently again. This is one OR4 iCon 120 Blue Plus, measured on a 5 × 12 grid at five distances from the fixture, water depth 55 cm (22 in).
| Distance from light | Peak PAR | Centre average | Grid average | Points lit |
|---|---|---|---|---|
| 15 cm 6 in | 577 | 526 | 530 | 12 / 60 |
| 30 cm 12 in | 253 | 230 | 118 | 36 / 60 |
| 60 cm 24 in | 122 | 116 | 93 | 36 / 60 |
| 90 cm 35 in | 80 | 78 | 55 | 60 / 60 |
Orphek OR4 iCon 120 Blue Plus, one bar, measured PAR (PPFD).
How to read a PAR map
A PAR map is the grid itself rather than its summary. Each cell is one measurement at one point.
Read down the series to see the trade. Raising a fixture always costs intensity and always buys coverage. The maps make the exchange rate visible, and the right answer depends on your tank's depth, your aquascape and what you keep.
What PAR does not tell you
Plenty. Spectrum is invisible to a PAR meter, two fixtures can read identically and look and perform completely differently. Your aquascape shades; a tall rock structure can drop the reading behind it to a fraction of the open-water value. Where you place a coral matters more than the fixture's headline figure, because the same tank is several light environments between sand bed and top rock. And acclimation matters: corals respond to change over time, not just to a number.
Treat published PAR as what it is: a measured, checkable starting point, rather than a promise about your tank.
Why we publish this
Because almost nobody does. The hobby has outsourced the question to third-party testing, which means buyers comparing fixtures are mostly comparing marketing language.
We would rather publish the grids, including the rows that are less flattering, and be held to them. If you measure one of our lights and get something different, we want to hear about it.
Common questions
What is PAR in a reef aquarium?
PAR stands for Photosynthetically Active Radiation: the band of light between 400 and 700 nanometres that drives photosynthesis. In a reef tank it is the light your corals can actually use, as distinct from how bright the tank looks to your eye. A PAR meter reports how much of that band arrives at one specific point.
What is the difference between PAR and PPFD?
PAR is the range of light that drives photosynthesis (400–700nm). PPFD, Photosynthetic Photon Flux Density, is the measurement of how much of it reaches a given point, expressed in micromoles of photons per square metre per second (µmol m⁻² s⁻¹). When a reefer says "300 PAR at the sand bed" they mean 300 PPFD. Even PAR meters report PPFD.
Why is a single PAR number misleading?
Because PPFD is a point measurement, and a light is not a point. On the Orphek Natura iCon MAX at 15 cm from the fixture, the peak reading is 1820 PAR, but only 32 of the 72 measured points register any light at all. The same fixture at 60 cm reads 515 at peak with every one of the 72 points lit. One headline number can describe either of those situations.
How do you read a PAR map?
A PAR map is a grid of readings taken across the area a fixture covers, at a set distance from it. Each cell is one measurement. Reading across shows how evenly light spreads; reading down a series of maps taken at increasing distances shows the trade between intensity and coverage.
Do LED manufacturers publish PAR data?
Almost none do. The hobby relies on third-party testing instead. Orphek publishes full measured grids for its fixtures, every reading, not just the flattering one.
Can you compare PAR between different reef lights?
Only carefully. A PAR meter counts photons between 400 and 700 nanometres, so two fixtures with different spectrums are not directly comparable on PAR alone. A blue-heavy LED bar puts much of its output near the edges of that window, while a full-spectrum fixture spreads across it. Compare like with like, and always compare coverage as well as peak.
See the full data. Complete measurement grids, every reading, for the Natura iCon MAX and the OR4 iCon Blue Plus.
Not sure what your tank needs? Our compatibility chart specifies configurations for 50 aquarium models.
