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Choosing a light for a planted tank seems simple… until you’re staring at specs about Kelvin, PAR, and beam angles. The truth is, there isn’t one “best” light for everyone. The right choice depends on your plants, your tank dimensions, and how much maintenance you want. This guide breaks lighting down into three essentials: color spectrum, intensity, and spread, and then shows how to match a fixture to your goals without guesswork.
Color Spectrum: Make the Tank Look the Way You Like
“White” light isn’t one color. It ranges from warm café tones around 2700 K to cool, bluish hues above 10,000 K. Plants can photosynthesize under a wide range of color temperatures, so the spectrum is mostly about human preference. Many aquarists settle in the 5,000 - 6,500 K window because it resembles daylight: greens look vivid, reds pop, and fish colors stay natural. Extremely blue fixtures designed for reef aquariums can wash freshwater scapes, while very warm lamps can tint foliage yellow. Pick the white you enjoy looking at every day, and your aquatic plants will be just fine.
Light Intensity: Match Brightness to Plant Ambition
Intensity is the fuel that drives growth. Low-intensity lights are perfect for Anubias, Java fern, Cryptocoryne, and other undemanding species. Medium intensity opens the door to most stem plants. High intensity grows carpets and color-hungry reds, but it also increases the need for CO₂ and consistent fertilization to keep algae in check. The technical yardstick is PAR (Photosynthetically Active Radiation), but PAR varies with tank height, distance from the light, lids, and even plant placement, so many brands don’t publish a single number. A practical rule: taller fish tanks need stronger lights to push photons to the substrate; shallow tanks can run gentler fixtures.
For reliability and efficiency, choose LED over legacy fluorescent/CF bulbs. LED fish tank lights offer high brightness, low power draw, long life, and-usefully-dimming. A dimmer lets you start low for easy plants and nudge upward later without buying a new fixture.
Light Spread: Cover the Whole Aquascape
A fixture can be blindingly bright at the center and still starve the corners; what matters is how evenly photons land across the footprint at plant height. Most bar lights cast a roughly 12 in (30 cm) “sweet zone” directly under the diodes. If your tank is 18–24 in (46–61 cm) front-to-back, plan for either two parallel fixtures, a unit with a wide optic (≈120° beam), or a broad, shop-style lamp (noting these can render colors less vividly). Braced rims, glass lids, and condensation trays narrow spread and cut intensity, so expect to bump output or raise the fixture to compensate.
Think in footprints, not lumens. Measure the tank’s front-to-back width and compare it with the light’s stated beam angle; if the specs are vague, assume ~12″ of even coverage and design for overlap. Mounting height also shapes spread: raising the light 2–6 in (5–15 cm) softens hotspots, fills edges, and reduces foreground glare, at the cost of some intensity (which you can recover by dimming up a notch). Conversely, very close mounts punch hard directly below but create stark falloff and shadow bands behind tall hardscape.
Hardscape and plant masses cast real shadows. To avoid “striping” behind wood/rocks, use cross-lighting (two bars spaced front/back) so one fills the other’s shadow. On very wide tanks, three slimmer fixtures often give cleaner uniformity than one ultra-bright bar. If you’re stuck with a single light, try centering slightly forward to brighten the carpet while letting reflections off the back glass lift rear shadows.
Putting it Together: Pick the Right Light for Your Goal
Goal: Hassle-free Greens, Minimal Maintenance
Choose a dimmable LED in the 5,000–6,500 K range. Run 6-8 hours/day on a timer. Keep intensity modest for Ferns, Epiphytes, and Crypts. Dose a comprehensive all-in-one liquid fertilizer weekly and add root tabs beneath heavy root feeders.
Goal: Stems with Shape and Some Color
Use a medium output LED capable of reaching the substrate at your tank height. Start at ~70% brightness and 8 hours/day; raise or lower in 10% steps every 1-2 weeks based on plant response. Maintain steady macronutrients (nitrate/phosphate) so stems don’t stall.
Goal: Carpeting Plants and Deep Reds
Pick a high-output LED with good spread and plan for pressurized CO₂, robust fertilization, and diligent pruning. Begin conservatively (60-70% power, 6 hours), then increase only as plant mass and CO₂ stability allow. Highlight without matching CO₂/nutrients invites algae.
A Simple Setup Routine That Works
- Mount & center the fixture so the beam edge just kisses the front and rear glass; this evens out intensity from foreground to background.
- Timer to the rescue: start 6-8 hours/day for new scapes; extend to 8-10 hours once plants are dense and stable.
- Dim for success: if your light has levels, begin at 50-70%. Make changes no more often than weekly; plants need time to respond.
- Balance the trio: light, nutrients, and carbon (ambient or injected). If you raise one, the others should rise proportionally.
- Watch the plants, not the calendar: compact new growth, healthy color, and little to no algae = on track. Long internodes, pale tops, or dust algae = adjust intensity/photoperiod or dosing.
Common Lighting Mistakes (and Quick Fixes)
- Too much, too soon: blasting a brand-new tank with high light before roots establish. Fix: shorten to 6 hours, dim 10-20%, add fast growers to soak up nutrients.
- Uneven coverage: bright center, dim corners. Fix: raise the fixture slightly, add a second bar, or choose a wider-beam light.
- Chasing “PAR numbers” blindly: ignoring tank height, lids, and layout. Fix: evaluate at the plant level. If foreground shadows persist, you need more spread or intensity.
- Ignoring maintenance: old leaves and detritus fuel algae on bright schedules. Fix: weekly trims, filter care, and gravel-vacs keep light working for plants, not against them.
Quick Chooser by Tank Size & Height (Guideline)
Shallow Nanos (≤12″ / 30 cm tall)
A single dimmable LED with a wide optic (≈120°) mounted 2-4″ above the rim usually blankets the footprint. Aim for roughly 30–60 µmol/m²/s PAR at the substrate to grow easily and many medium plants without forcing CO₂. Start at 50-60% brightness for 6-8 hours, then nudge up in 10% steps as plant mass increases. Great candidates include Anubias, Bucephalandra, Java fern, Cryptocoryne, Hydrocotyle tripartita, Hygrophila, and even Monte Carlo in high-density, shallow layouts. Keep the flow gentle but even; shallow tanks can hotspot, so raise the fixture slightly if you see harsh shadows or algae in the foreground.
Standard Tanks (16–21″ / 40–53 cm tall)
Choose a mid-output LED capable of delivering 40-80 µmol/m²/s at the substrate; tank lids and braces will reduce intensity, so account for that. If the aquarium is 18–24″ front-to-back, consider two bars or one unit with a truly wide beam so corners aren’t starved. Begin around 60-70% brightness for 7-8 hours and stabilize nutrients (root tabs under rosettes; all-in-one liquid for stems/epiphytes). Expect reliable growth on most stems (Ludwigia, Rotala, Bacopa), Crypts, Swords, and easier carpets (dwarf sag, Hydrocotyle). CO₂ is optional for greens but becomes increasingly helpful for compact carpets and tidier internodes as you approach the top of that PAR range.
Tall Displays (≥24″ / 61 cm tall)
Prioritize higher output and optics that maintain intensity at depth; target 60–100+ µmol/m²/s at the substrate if carpeting or red, high-light stems are on the menu. Many tall tanks benefit from dual fixtures or a single high-power unit raised 3-6″ to improve spread while running at 70–90% brightness. Start conservatively at 60-70% for 6-7 hours, add pressurized CO₂, and scale macronutrients to match the light. This trio prevents algae while letting carpets (dwarf hairgrass, HC) and reds (Alternanthera, Rotala ‘H’ra’, Ludwigia sp.) color up. Ensure strong, even circulation so CO₂-rich water reaches the bottom; dead zones in tall columns stall carpets first. If you prefer no CO₂, cap intensity lower, extend the photoperiod slowly to 8 hours, and focus on deep-rooted greens and mid-light stems for a stable, low-maintenance scape.
Bottom Line
Pick a spectrum you enjoy, ensure enough intensity at plant height, and cover the whole footprint with a suitable spread. Set a timer, dim to start, and change settings slowly. When light, nutrients, and (optionally) CO₂ move together, plants thrive and algae fade into the background.
Want help sizing a light for your exact tank (dimensions, scape, plant list)? Share the details, and Splashy Fish will recommend output and photoperiod settings you can use on day one.
Aquarium Lights Frequently Asked Questions (FAQs)
What Is the Best Aquarium Light for Plants?
The best aquarium light depends on your tank size, plant types, and budget. For most planted tanks, a full-spectrum LED light is ideal because it mimics natural sunlight and supports healthy growth and vibrant colors. The Aqua Worx SOL is a great budget-friendly option that delivers a balanced spectrum while enhancing the tank’s appearance. For stronger output and wider coverage, the Lifegard Full Spectrum 2.5' LED offers excellent brightness and simple plug-and-play installation. Both options provide reliable performance for growing lush, healthy aquatic plants in freshwater aquariums.
What Kind of Light Do You Need for a Planted Aquarium?
Planted aquariums need full-spectrum lighting that supports photosynthesis and mimics natural sunlight. The most common options are T8 and T5 fluorescent bulbs. While both can grow aquatic plants, T5 bulbs are more powerful and better suited for densely planted tanks or demanding plant species. One full-length T5 fixture is often enough for most standard aquariums. Many aquarists now prefer LED lights, which provide excellent brightness, color balance, and energy efficiency. Whether fluorescent or LED, choose lighting that covers the full tank evenly and runs about 8-10 hours per day.
What Color LED Light Is Best for Growing Plants?
For healthy aquarium plant growth, a mix of blue and red light works best. Blue light promotes chlorophyll production, encouraging strong leaf and root development, especially in young plants. Red light supports overall growth and helps plants produce new shoots and flowers. Green light, while less critical, enhances appearance and contributes to balanced photosynthesis. Most full-spectrum LED lights combine all these wavelengths to mimic natural sunlight, providing both optimal growth and beautiful color rendering for your aquarium. Using a balanced light spectrum ensures vibrant plants and a visually stunning tank.
