Aquarium Lighting Calculator
Calculate PAR, Lux & total lumens for your tank – based on real dimensions, reflector quality and light type.
- Low light: ≤ 30 PAR — epiphytes, mosses, shade plants
- Medium light: 30–50 PAR — most stem plants
- High light: > 50 PAR — carpeting plants & demanding species
FAQ
What is a good PAR for planted aquariums?
As a practical baseline, aim for 20–40 PAR at the substrate for low-light tanks, 40–80 PAR for most planted layouts, and 80–150+ PAR for demanding carpets and high-light stems.
What does “PAR at substrate” actually mean?
It’s the usable plant light that reaches the bottom of the tank. This matters more than surface brightness because plants (especially carpets) live and compete down there.
Why can two LED lights with the same watts produce different PAR?
Because diode efficiency, optics, spectrum, mounting height, and spread change how much usable light reaches the substrate. Watts describe power draw, not plant intensity.
Is watts per liter (or watts per gallon) still useful?
Only as a rough starting point. For planted tanks, PAR at substrate is more reliable because it includes tank depth and real-world light loss.
How does tank height affect the PAR I need?
Taller tanks need more output because water and distance reduce intensity. If you increase height, you usually compensate via stronger fixtures, lower mounting height, or higher channel power.
Does mounting height change PAR and plant growth?
Yes. Lower mounting increases PAR but can create hotspots. Higher mounting improves spread and uniformity but reduces PAR. Most tanks benefit from “even coverage” over maximum peak.
Do I need CO₂ if I run high PAR?
Often, yes. Higher PAR increases plant demand for CO₂ and nutrients. Without matching CO₂/fertilization, growth stalls and algae becomes more likely.
Why did algae appear after increasing light?
Light is the accelerator. If CO₂, nutrients, or maintenance don’t scale with it, algae gains the advantage. Reduce intensity/photoperiod, stabilize CO₂, and keep nutrients consistent.
What photoperiod should I use for a new planted tank?
Start conservative: 6 hours/day is a common baseline. Increase slowly only when plants are stable. Many algae issues come from long photoperiods with unstable CO₂.
Lux vs lumens vs PAR: what should I trust?
PAR (PPFD) is the best plant-focused metric. Lux and lumens can help compare brightness, but they’re influenced by spectrum and don’t translate cleanly to plant growth.
How do tannins or cloudy water affect lighting?
They reduce light penetration. In blackwater or turbid tanks you often need more output (or shorter distance) to reach the same substrate PAR.