Lighting Calculator

🔆 About This Aquarium Lighting Calculator

This calculator helps you estimate PAR (Photosynthetically Active Radiation) and DLI (Daily Light Integral) at three depths in your aquarium: surface, mid-water, and substrate. It is designed for planted tanks and uses real-world data from hobbyists, manufacturers, and scientific sources.

How it works (step by step):

1. You enter – your tank dimensions, light distance, water clarity, bulb type, lumens, spectrum, and photoperiod.

2. The calculator converts lumens into lux on the water surface based on:

   – Total lumens × reflector efficiency ÷ tank surface area
   – A distance factor (light height above water): 1 / (1 + distance_cm / 30).

3. It then calculates lux at depth using Beer‑Lambert attenuation:
   Lux(depth) = Lux(surface) × e^(-k × depth_cm)
   where k depends on water clarity (0.025 for clear, 0.045 for slight tannins, 0.070 for blackwater).

4. Lux values are converted to PAR (μmol/m²/s) using a spectrum‑dependent factor:
   PAR = Lux × factor. For example:
   – Daylight 6500K: 0.012
   – Red+Blue+White: 0.014
   – Other spectra: between 0.011 and 0.012

5. DLI (mol/m²/day) is calculated as:
   DLI = PAR × 3600 × photoperiod_hours / 1,000,000

Why these numbers?

• The PAR ranges (Low <30, Medium 30–60, High >60) are based on practical observations from experienced aquascapers (George Farmer and Tom Barr). These values work in real tanks with proper CO₂ and flow.

• DLI thresholds (0.8–1.5 Low, 1.5–2.5 Medium, 2.5–4.0 High, >4.0 Very high) are scaled to match the PAR ranges above and typical photoperiods of 8–12 hours.

⚠️ Important limitations & approximations

Even with careful calibration, every calculation is an estimate. The following factors are simplified or ignored in this calculator:

• Reflector efficiency varies greatly between fixtures. I used typical values (LED without reflector: 0.65, with reflector: 0.80) but real efficiency can be 0.5–0.95.

• Spectrum conversion (Lux → PAR) depends on the exact SPD (Spectral Power Distribution) of your light. The fixed factors are averages.

• Water attenuation is affected by dissolved organic matter, floating plants, biofilm, and even the angle of the light. The constants used here are generic.

• Light distribution is assumed uniform across the whole surface. In reality, most fixtures have a so-called “hot spot” directly under them and lower PAR at the edges.

• Hardscape and plants can also block light, therefore, in calculation, I assume an empty tank with clear water.

• PAR meters measure differently (quantum sensor vs. cheap smartphone apps). Results from different meters may vary by 10–20%.

✅ How to get the most reliable result

• Use the lumens value printed on your light’s packaging (not watts).

• If your light has a reflector, lens, or optics, choose “LED with reflector/optics”.

• For most white LED fixtures (6500K), select “Natural Daylight 6500K”.

• If you have a lux meter, switch to “Measured Lux” mode and enter a real reading from the substrate level.

Frequently Asked Questions