Aquarium PAR Calculator
Calculate PAR at substrate, Lux & total lumens for your aquarium — based on tank dimensions, mounting height, water clarity and reflector efficiency.
Updated for modern LED aquarium lighting (2026).
Advanced: enter your measured lux value (for example from Photone). We’ll estimate PAR at the substrate using water clarity + depth.
Measure with the sensor touching the water surface (inside water) or at a known depth in water. Measurements in air will overestimate PAR unless you switch Measured in air.
FAQ
What is a good PAR for planted aquariums?
As a practical guideline at the substrate: ≤ 30 PAR for low-light tanks (epiphytes and shade plants), 30–60 PAR for most planted aquariums, and ≥ 60 PAR for carpeting plants and demanding species.
What does “PAR at substrate” actually mean?
It’s the usable plant light that reaches the bottom of the tank. This value matters more than surface brightness because plants — especially carpets — grow and compete at the substrate level.
Why can two LED lights with the same watts produce different PAR?
Because diode efficiency, optics, spectrum, mounting height, and light spread all affect how much usable light actually reaches the substrate. Watts describe power consumption, not plant intensity.
Is watts per liter (or watts per gallon) still useful?
Only as a rough reference. For planted tanks, PAR at the substrate is far more reliable because it accounts for tank depth and real-world light loss.
How does tank height affect the PAR I need?
Taller tanks require more output because water depth reduces light intensity. This is usually compensated with stronger fixtures, lower mounting height, or higher channel output.
Does mounting height change PAR and plant growth?
Yes. Lower mounting increases PAR but can create hotspots. Higher mounting improves spread and uniformity while reducing PAR. In most tanks, even coverage is more important than peak intensity.
Do I need CO₂ if I run high PAR?
In most cases, yes. Higher PAR increases plant demand for CO₂ and nutrients. Without matching supply, growth stalls and algae becomes more likely.
Why did algae appear after increasing light?
Light acts as an accelerator. If CO₂, nutrients, or maintenance don’t scale with it, algae gains the advantage. Reduce intensity or photoperiod first, stabilize CO₂, and keep nutrients consistent.
What photoperiod should I use for a new planted tank?
Start conservatively with 6 hours per day. Increase slowly only once plants are stable. Many algae problems come from long photoperiods combined with unstable CO₂.
Lux vs lumens vs PAR: what should I trust?
PAR (PPFD) is the most plant-relevant metric. Lux and lumens can help compare brightness, but they depend heavily on spectrum and don’t translate directly to plant growth.
How do tannins or cloudy water affect lighting?
They reduce light penetration. In blackwater or turbid tanks, you usually need more output or shorter mounting distance to reach the same PAR at the substrate.