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Reef + Planted Aquarium DLI Calculator

PAR alone doesn't tell you whether your corals are getting enough light. Daily Light Integral — the total mol of photons per m² per day — is the metric that matters because coral photosynthesis integrates over time. This calculator converts your peak PAR reading and photoperiod into DLI and compares it against published target bands for softies, LPS, SPS, clams, and planted tanks.

reefcalcs editorialUpdated Reviewed for accuracy 4 sources cited(calculator)

Daily Light Integral

From your meter, at the measurement point. Use the par-underwater calc if you need to correct for an in-air sensor.

Excludes ramp time.

Lights-on to lights-off, including ramp up/down.

DLI (ramped, realistic)
6.75mol/m²/day
DLI (peak-only, ceiling)
7.20mol/m²/day

Assumes all hours run at full peak — overestimate.

Target band
6–12mol/m²/day
Hours-at-peak to hit target middle
10.0hr

Given your current peak PAR — schedule recommendation.

GOOD — within target band

DLI = PAR × hours × 0.0036. The ramped value averages at ~75 % of peak across the photoperiod (typical reef-LED ramp shape). Target bands from Joshi's PAR-by-fixture data and the BRS reef lighting cheat sheet.

Gear for thisAffiliate links

Apogee MQ-510 Underwater PAR Meter

~$575 · View on Amazon →
EcoTech Radion XR15 Pro (G6)~$500 · View on Amazon →

Affiliate links. As an Amazon Associate, reefcalcs earns from qualifying purchases.

How this is calculated

DLI (mol/m²/day) = PAR (μmol/m²/s) × hours × 3600 / 1,000,000
                = PAR × hours × 0.0036

Two estimates reported:
  Peak-only DLI    = peak_PAR × hours_at_peak × 0.0036
  Ramped DLI       = peak_PAR × 0.75 × total_photoperiod × 0.0036
                     (averages 75% of peak across a typical reef-LED ramp)

Target bands (mol/m²/day):
  Reef corals
    Softies / zoas             2  – 6
    LPS                        4  – 9
    SPS — mid light            6  – 12
    SPS — high light           10 – 18
    Clams (Tridacna)           8  – 14
  Planted (freshwater)
    Low light                  4  – 8
    Medium light               8  – 15
    High light (CO₂ required)  15 – 30

The peak-only estimate is the ceiling — what the DLI would be if the fixture ran at full intensity for the entire peak window. The ramped estimate is the realistic value, calibrated against the shape of typical reef-LED schedules (1–2 hours up, 6–8 hours peak, 1–2 hours down).

DLI is more honest than PAR for two reasons. First, photosynthesis is rate-limited at high intensities — pushing peak PAR past saturation doesn't add growth, just adds heat. Second, corals and plants adapt to total integrated light over weeks, not to peak values, so a long-low photoperiod can produce identical growth to a short-high one at the same DLI.

Practical implication: if your DLI is short of target, extend the photoperiod first (cheap), then raise intensity (expensive, more bleach risk). If your DLI is over target, shorten the photoperiod first — never reduce intensity below 60 % unless you're acclimating new coral.

FAQ

What's a good DLI for a mixed reef tank?
6–10 mol/m²/day measured at the lowest coral in the tank. That covers softies, LPS, and most SPS. Top frags will see 12–18 DLI because they're closer to the light, which is what high-light SPS want.
Is DLI better than PAR for setting up lighting?
They're complementary. PAR tells you the intensity at a point right now; DLI tells you the cumulative light dose per day. Coral and plant biology cares about DLI; sensor measurements give you PAR. Use both — measure PAR, calculate DLI.
Why does ramping matter?
An LED that ramps over 8 hours doesn't run at peak for 8 hours — typical schedule is 1–2 hours ramp up, 5–6 hours at peak, 1–2 hours ramp down. The ramped DLI estimate (peak × 0.75 × total) catches this. Apex/Kessil/AI schedules vary; the 0.75 factor is the consensus average.
Can I just run more hours at lower intensity?
For corals: usually no. Most reefers report bleaching at long-low schedules because the spectral output of dimmed LEDs shifts blue-heavy and stresses zooxanthellae. Stick with industry-norm photoperiods (8–12 h total) and tune peak intensity.
What's the difference between DLI for coral vs planted tanks?
Planted tanks generally want higher DLI because terrestrial plant ancestors evolved under full sun. High-light planted setups (CO₂-injected) target 15–30 DLI — double or triple a typical reef. Low-light planted (Walstad / dirted) target 4–8 DLI, similar to softies.

Where to buy

Affiliate links

Most modern reef LEDs can hit any of these DLI targets at typical hanging distances. Tune the schedule, not the fixture.

AI Hydra 32HDStandard SPS-grade fixture. 24×24 in footprint at SPS PAR.View on Amazon →EcoTech Radion XR15 Pro (G6)Best programmable channel control. 24×24 in SPS-grade.View on Amazon →Kessil A360X Tuna BluePendant-style. Best 'shimmer' in the hobby. 24×24 in coverage.View on Amazon →

Affiliate links. As an Amazon Associate, reefcalcs earns from qualifying purchases.

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Sources & references

  1. 1.
    Sanjay Joshi — Practical aspects of PAR measurements
    https://reefs.com/magazine/practical-aspects-of-photosynthetically-active-radiation-par-measurements-using-a-par-meter/
  2. 2.
    Bulk Reef Supply — reef lighting cheat sheet (PAR by coral target)
    https://www.bulkreefsupply.com/content/post/reef-tank-lighting-overview
  3. 3.
    Reef2Reef — Easy DLI calculator & findings thread
    https://www.reef2reef.com/threads/reef-lighting-easy-dli-calculator-findings.1038746/
  4. 4.
    Buce Plant — aquarium plant lighting requirements
    https://buceplant.com/blogs/aquascaping-with-bucephalandra/aquarium-plant-light-requirements

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