Aquarium Lighting & Photoperiod Calculator

Plan PAR targets, watts-per-gallon (WPG) proxies and a clean day/night schedule. Pick a preset (plants or corals), enter tank size, and get recommended intensity and duration with LED/T5/MH power suggestions.

Tank & Dimensions
Lighting Profile & Preset
Photoperiod
Fills a sensible schedule for your preset.

Lighting Targets & Schedule

Select a preset and enter dimensions to see target PAR/WPG, estimated fixture power for LED/T5/MH, and a day plan.

Tank Volume
—
Computed from entered dimensions
Target PAR
—
Preset range (mid-point used if no override)
WPG Proxy (T5 baseline)
—
Rule-of-thumb only (cross-check)
Estimated Fixture Power
—
LED / T5 / MH suggestion for your size & preset
PAR at Depth (est.)
—
Accounts for clarity, water height & mount (proxy)
Photoperiod Plan
—
Start → ramp → peak → ramp → blue

How the Aquarium Lighting & Photoperiod Calculator Works

This planner pairs PAR targets with a conservative WPG proxy to estimate fixture power and a stable photoperiod. PAR is the preferred metric for plant/coral growth; WPG is provided as a legacy cross-check. We adjust expected PAR at depth using a simple attenuation model for water height, clarity, and mounting height. Always fine-tune with a PAR meter where possible.

Suggested PAR Targets

  • Low-light plants: 20–40 PAR at substrate.
  • Medium plants: 40–80 PAR at substrate.
  • High-tech (CO₂): 80–120 PAR at substrate.
  • FOWLR: 20–50 PAR (display top).
  • Soft corals: 75–150 PAR (top-mid).
  • LPS: 100–200 PAR (mid-low).
  • SPS: 200–350+ PAR (top, shallow).

Spectrum & Intensity — Practical Notes

  • Freshwater plants: Full-spectrum (5–7K CCT) with strong red (~660 nm) and blue; avoid long peaks over 8 h without CO₂.
  • Reef: Heavy blue/violet (420–470 nm) for photosynthesis and fluorescence; white peak typically 5–8 h with extended blue.
  • Depth & clarity: Deeper or tannin-rich water needs more fixture output to deliver the same PAR at substrate.
  • Spread: Raise lights to widen spread but expect lower peak PAR; add fixtures for long tanks.

FAQs — PAR vs WPG, Photoperiod & Algae

Is WPG still valid?

WPG is a coarse proxy from T5 days. Use it only as a sanity check; PAR is the goal.

How long should I run the lights?

Plants: 6–8 h (low/med) or ~8 h (high-tech with CO₂). Reef: 9–12 h total with 5–8 h white peak and extended blue.

Why am I getting algae?

Excess intensity or long peak without matching CO₂/nutrients and stable filtration. Shorten peak or reduce intensity 10–20% and review fertilization.

Do I need a PAR meter?

Strongly recommended for dialing in intensity, especially for SPS. Use this planner to get close, then verify.