Aquarium Light PAR Required by Plant Calculator Guide
Light is the engine that drives every other planted-tank input — get it wrong and CO2 plus ferts cannot rescue the result. The aquarium light par calculator question matches plant species photosynthesis demand to the photon flux at substrate level, expressed as PAR in micromoles per square metre per second. This guide from Gensou Aquascaping at 5 Everton Park bands plants by light demand, gives PAR ranges from low to very high, and walks distance correction so you can spec a fixture for your specific tank height. The aquarium light par calculator is the single most important number a planted tank owner should know.
Quick Answer Rule of Thumb
Low light: 30-50 µmol/m²/s PAR at substrate — anubias, java fern, cryptocoryne, mosses. Medium light: 50-150 — ludwigia, rotala rotundifolia, monte carlo, micranthemum. High light: 150-300 — HC Cuba, glossostigma, red rotala, ammannia. Very high: 300+ — competition carpet plants, deep red macrandra, blyxa japonica massed. Most planted tanks live in the 60-120 PAR band.
The PAR Method
PAR (photosynthetically active radiation) measures the photon flux in the 400-700 nm wavelength range plants actually use. Lumen and lux ratings are useless for planted tanks because they weight the response curve to human eye sensitivity, not chlorophyll. Buy a PAR meter (Apogee MQ-510 around SGD 600) or trust manufacturer-published PAR data taken at fixture-mounted distance. Substrate PAR is the figure that matters, not water surface PAR.
The Plant Bands
Low-light epiphytes thrive at 30-50 PAR — anubias nana, java fern microsorum, bucephalandra, cryptocoryne wendtii, vesicularia mosses. Medium-light stems sit at 60-120 — rotala rotundifolia, ludwigia repens, hygrophila polysperma, lobelia cardinalis. High-light demanders need 150-250 — HC Cuba (Hemianthus callitrichoides), glossostigma, ammannia gracilis, rotala macrandra. Carpets and competition reds need 250-400 with strong CO2 to match.
Distance Correction
PAR drops with the inverse square of distance from the light source. A fixture rated 100 PAR at 30 cm reads roughly 56 PAR at 40 cm and 36 PAR at 50 cm. So a fixture mounted 30 cm above a 60 cm deep tank delivers 100 PAR at the surface but only 36 PAR at the substrate. For deep tanks, either pendant the fixture closer to the water (15-20 cm) or pick a higher-PAR fixture rated for the substrate distance.
Worked Example: 60 L Low-Tech Anubias and Crypts
Tank 60 cm wide, 30 cm front-to-back, 35 cm deep with 5 cm substrate. Distance from fixture to substrate: roughly 35-38 cm. Target substrate PAR 40-60. A 25-30W LED rated 80 PAR at 30 cm delivers around 50 PAR at the substrate — perfect for low-tech epiphyte landscapes from the aquarium lighting range. No CO2 needed at this band.
Worked Example: 120 L High-Tech Carpet
Tank 90 cm wide, 35 cm front-to-back, 40 cm deep. Distance to substrate: 45-50 cm. Target substrate PAR 200+ for HC Cuba carpet. A pair of 30W high-output LEDs rated 200+ PAR at 30 cm, mounted at 20 cm above water, delivers roughly 180-220 PAR at substrate. Pair with CO2 at 30 ppm and EI dosing — see the CO2 range for setup.
Worked Example: 200 L Mid-Tech Stem Tank
Tank 100 cm wide, 40 cm front-to-back, 50 cm deep. Distance to substrate: 55-60 cm. Target substrate PAR 100-150 for medium-light stems. Need a high-output fixture rated 250+ PAR at 30 cm, mounted at 20 cm above water, to deliver target PAR through the deeper water column. Skimping on light at 50 cm depth is the most common reason stem plants stretch and lose colour.
Singapore-Specific Variables
Tannin staining from leaf litter or driftwood reduces PAR transmission by 5-15 per cent — increase fixture rating accordingly. Algae on the glass cuts PAR another 10-20 per cent — clean weekly. LED fixtures degrade roughly 5 per cent per year of operation; budget replacement at year 4-5. Many Singapore-imported budget LEDs publish lumen specs without PAR — distrust those and stick to brands with measured data.
Common Pitfalls
Buying lumen-rated fixtures for planted use. Mounting too high to “spread the light” — drops PAR drastically. Running 12-hour photoperiods to compensate for low PAR — doubles algae risk without raising plant uptake meaningfully. Ignoring fixture spectrum — high-CRI 6500K LEDs grow plants better than 10000K marine spectrum. Skipping PAR meter rental and guessing.
When to Override the Calculator
Shaded sections under driftwood overhangs deliberately receive less PAR — choose anubias and bucephalandra for those zones regardless of fixture rating. Floating plants reduce mid-tank PAR by 30-50 per cent — useful for low-light fish in mostly-stem tanks. New plants benefit from 20 per cent reduced PAR for their first month while roots establish. Dim slightly and ramp up over weeks.
Related Reading
emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
