Which LED Aquarium Light Should I Buy?

Match the light to your tank type (freshwater planted vs. marine reef), use PAR targets instead of watts-per-gallon, choose a spectrum that suits plants or corals, and size for coverage + control. Here’s an evergreen, search-intent guide with the exact numbers and checklists hobbyists look for.

Step 1: Identify Your Tank Type

Freshwater (planted): Prioritize even spread, natural-white spectrum (5,000–7,000 K) with some deep red (~660 nm) and blue (450–470 nm) for photosynthesis.
Saltwater (reef): Prioritize blue-heavy (400–470 nm) output for PUR, strong punch for depth, controllable color channels, and shimmer.

Step 2: Use PAR Targets (not watts-per-gallon)

Freshwater Planted PAR at the Substrate

• Low light: 30–60 μmol/m²/s (easy plants, low CO₂)

• Medium: 60–100 μmol/m²/s (moderate plants, liquid carbon)

• High: 100–200 μmol/m²/s (carpets, reds, pressurized CO₂)

Reef PAR at Coral Level

• Softies: 50–100 μmol/m²/s

• LPS: 75–150 μmol/m²/s

• SPS: 200–350 μmol/m²/s (some thrive 250–400 with strong flow & nutrients)

Tip: Glass lids, braces, and water surface agitation can reduce PAR 10–25%. Measure after final setup.

Step 3: Spectrum That Works

Freshwater (Planted)

• 5,000–7,000 K white looks natural and grows plants well.

• Add 660 nm red and 450–470 nm blue for chlorophyll peaks.

• Avoid excessive UV for livestock comfort; a small UV-A touch is optional, not required.

Reef (Marine)

• Emphasize violet/royal blue/blue (400–470 nm) for PUR and fluorescence.

• Warm white is optional to balance color; most reefs run “blue-dominant” for health and pop.

• Aesthetics commonly resemble 14,000–20,000 K.

Step 4: Sizing for Coverage (Spread > raw power)

Use fixture spread and lens angle (90–120° typical) to cover the tank front-to-back. For deeper tanks (>50 cm water depth), pick lights with narrower optics or higher output to maintain PAR at the sandbed.

Quick coverage rules of thumb (typical modern LED panels/bars):

• 60 cm / 24 in long tanks: 1 small–medium fixture

• 90 cm / 36 in: 1 high-output or 2 small fixtures

• 120 cm / 48 in: 2 medium or 1 bar + 1 panel combo

• 180 cm / 72 in: 3 modules or 2 bars + 1 panel for uniformity

Stagger modules or mix panel + bar to eliminate dark zones near braces.

Step 5: Photoperiod & DLI

• Planted: 8–10 h total. Start ~8 h to manage algae; increase slowly.

• Reef: 9–12 h total with 1–2 h ramp sunrise/sunset. Blue-only “viewing” periods are fine, but keep high-intensity windows consistent.

DLI formula: DLI (mol·m⁻²·day⁻¹) = PPFD × hours × 0.0036
Example (planted medium): 70 PPFD × 9 h × 0.0036 ≈ 2.3 DLI at substrate (sufficient with balanced CO₂/nutrients).

Step 6: Mounting & Optics

• Height: Start 20–30 cm (8–12 in) above water for panels; bars can go closer for edge fill.

• Shimmer: Point-source clusters create strong shimmer; diffusers soften it (great for planted scapes).

• Glare control: Use shades/baffles if the tank is in living spaces.

Step 7: Hardware & Safety (Aquarium-specific)

• Ingress protection: IP65+ for splash; shields over lenses.

• Salt creep resistance: Marine setups prefer sealed housings, stainless fasteners, and conformal-coated boards.

• Thermals: Heatsinks or quiet fans keep LED junction temps low and output stable.

• Control: Onboard dimming plus app/0–10 V; reef prefers multi-channel control (UV/violet/royal/blue/white separately).

• Power: Drip loops, GFCI/RCD, and raised power strips—always.

Recommended PAR by Biotope (Bookmark This)

Acclimation (Avoiding Shock & Algae)

• Start at 30–50% intensity and increase 5–10% per week.

• Keep nutrients stable; more light requires more CO₂ (planted) or balanced NO₃/PO₄ (reef).

• Re-measure PAR after any height, lens, or aquascape change.

Buyer’s Checklist (SEO-Friendly)

Must-haves

• Proven PAR output maps over standard tank sizes

• Channel control (at least 4+ for reef; 2–3 fine for planted)

• Reliable mounting and splash protection

• Solid thermal design and 3–5 year warranty

Nice-to-haves

• Diffuser (planted) or narrow optics (deep reef)

• Lunar mode, acclimation wizard, schedule library

• Bar add-ons to fill edges/front glass

Troubleshooting Quick Hits

• Algae blooms (planted): Lower intensity or shorten photoperiod; verify CO₂ (~20–30 ppm) and nutrient balance.

• Coral paling (reef): Too much PAR or too fast a ramp; reduce 10–20% and extend acclimation.

• Shadowing: Add a bar at the front or raise the fixture slightly to widen spread.

• Color dullness: Reef—add violet/royal-blue intensity; Planted—ensure 660 nm red is present (don’t overdo it).

FAQs

Q1: Do I need a PAR meter?
Highly recommended. Even a budget meter or a well-documented PAR map beats guessing.

Q2: Can one fixture do both planted and reef?
Not ideally. Reef needs stronger blue/PUR and higher PAR; planted prefers balanced white with some red.

Q3: Are RGB fixtures good for plants?
RGB alone is inefficient for growth. Use full-spectrum white with supplemental red/blue; keep RGB for accent.

Q4: How long do LEDs last?
Quality lights often rate 50,000 h (L70); lifespan depends on heat, splash protection, and salt creep management.

Q5: Should I run glass lids?
They reduce evaporation but can cut PAR and trap heat. If used, account for 10–25% PAR loss and clean weekly.

TL;DR

Pick your light by tank type, PAR target, and spread—not watts. For planted tanks, aim 30–200 PAR at the substrate depending on goals; for reefs, 50–350 PAR at coral level with blue-heavy spectrum. Get reliable control, protect against splash/salt creep, acclimate slowly, and re-check PAR whenever you change anything. Your aquascape (and livestock) will reward you.