Introduction: why calculation is fundamental
One of the most common mistakes among indoor growers is to choose lamps approximately — too few and plants suffer from a lack of light, too many and you risk heat stress and energy waste. In this guide we show you how to accurately calculate how many HortiSpectra lamps you need for your grow room.
Step 1: measure your cultivation area
The first step is to know the cultivation area in square metres. Measure the length and width of the space where you will place the plants and multiply them together.
Example: a grow room of 2m x 1.2m = 2.4 m² of cultivation area.
Step 2: Determine the target PPFD
Based on the cultivation phase and the species, establish the PPFD you want to achieve:
Vegetative phase: 400–600 μmol/m²/s
Flowering phase: 600–900 μmol/m²/s
High intensity crops: 900–1200 μmol/m²/s
For most crops, a target of 700–800 μmol/m²/s in flowering is an excellent starting point.
Step 3: calculate the total photon flow required
Multiply the target PPFD by the cultivation area:
Total flow (μmol/s) = PPFD target x Area (m²)
Example: 750 μmol/m²/s x 2.4 m² = 1,800 μmol/s total required.
Step 4: check the photonic flow of the lamp
Each HortiSpectra lamp has a total photonic flow value indicated in the technical specifications (expressed in μmol/s). Divide the total flow required for the flow of the single lamp:
N° lamps = Total flow required ÷ Single lamp flow
Practical example with HortiSpectra B600 ProMax
The B600 ProMax HortiSpectra has an efficiency of 3.15 μmol/J and a consumption of 600W, so it produces about 1,890 μmol/s.
For our 2.4 m² grow room with a target of 750 μmol/m²/s:
Required flow: 1,800 μmol/s
B600 ProMax flow: ~1.890 μmol/s
Result: 1 B600 ProMax lamp is enough to cover 2.4 m² with excellent PPFD values
Example with HortiSpectra B300 Plus X2 ProSeries
The B300 Plus X2 ProSeries is ideal for smaller spaces or for those who want more flexibility. With a consumption of 300W and the same efficiency, it produces about 945 μmol/s.
For a space of 1.2 m² with a target of 750 μmol/m²/s:
Required flow: 900 μmol/s
Flow B300 Plus X2: ~945 μmol/s
Result: 1 B300 Plus X2 lamp is perfect for 1–1.2 m²
Practical advice for your setup
Installation height: HortiSpectra lamps must be installed 40–60 cm from the canopy for optimal PPFD values and uniform coverage
Wall reflectivity: white or Mylar-coated walls increase light efficiency by 20–30%
Dimmer: use the Dual-Channel to adjust the intensity according to the phase and sensitivity of the plants
Ventilation: make sure you have a good air exchange to maintain optimal temperatures under the lamps
Conclusion
Correctly calculating the number of lamps is not complicated — just know the growing area, the target PPFD and the technical specifications of the lamp. With HortiSpectra lamps you have precise and verified technical data available to plan your setup with confidence.
Do you have doubts about your specific setup? Contact us — we are here to help you find the perfect solution for your grow room.
🌱 HortiSpectra – Grow Strong & Healthy.