Growth planning

Aquarium PAR Lighting Calculator

Estimate PAR at substrate, lux, light loss, and plant-light category.

  • PAR zones
  • Lux support
  • Plant targets

Calculator

Estimate light at substrate level

Units
Choose your goal
What do you want to grow?

Not sure? Mixed planted tank is a safe starting point.

Enter aquarium dimensions

Measure the usable inside length between the glass panels.

cm

Measure from the front glass to the back glass inside the aquarium.

cm

Measure from the bottom glass to the water surface. Average substrate depth is subtracted to estimate the light path to plants.

cm

Use the front-to-back average if the substrate is strongly sloped.

cm
Describe water and mounting conditions

Measure vertically from the underside of the light to the water surface.

cm

Suspended particles and tannins reduce the light reaching deeper plants.

Current aquarium light

Enter the specifications of a light or lighting combination you are considering.

Select your aquarium light

Choose a verified model to apply its technical specifications.

Each light must be the same selected model.

Luminous efficacy

Keep the automatic estimate unless the manufacturer provides a reliable luminous-efficacy value.

Choose the closest option only when the fixture's optical design is known. Otherwise, keep the automatic standard estimate.

Current aquarium light: lux measurement

Enter where and how the lux reading was taken so the calculator can estimate the light reaching the substrate.

Enter the stable reading shown by the lux meter at the selected sensor position.

lux
Measurement position

Immediately above the water surface. The current model does not use an additional sensor-height input.

Measure vertically from the water surface to the sensor.

cm

Choose the closest light type, or enter a calibrated conversion supplied by the manufacturer.

Enter the calibrated lux-per-PAR value for this light and meter combination.

lux/PAR

Aquarium Lighting Calculator FAQ

What is a good PAR for planted aquariums?

As a practical guideline at the substrate: <= 30 PAR for low-light aquariums, 30-60 PAR for most planted aquariums, and >= 60 PAR for carpeting plants and demanding species.

What does PAR at substrate mean?

It is the usable plant light that reaches the bottom of the aquarium. This value matters more than surface brightness because plants, especially carpets, grow and compete near the substrate.

Why can two LED lights with the same watts produce different PAR?

Diode efficiency, optics, spectrum, mounting height, and light spread all affect how much usable light reaches the substrate. Watts describe power consumption, not plant intensity.

Is W/L still useful?

Only as a rough reference. PAR at the substrate is more reliable because it accounts for aquarium depth, mounting distance, water clarity, and real-world light loss.

How does aquarium height affect lighting?

Taller aquariums need more output because water depth reduces light intensity. Stronger fixtures, shorter mounting distance, or higher channel output can compensate.

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 do not scale with it, algae gains the advantage. Reduce intensity or photoperiod first, then stabilize CO2 and nutrients.

Lux vs lumens vs PAR: what should I trust?

PAR, or PPFD, is the most plant-relevant metric. Lux and lumens help compare brightness, but they depend heavily on spectrum and do not translate directly to plant growth.

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