Calculator Inputs
Example Data Table
| Room (m) | Stage | Target (lux) | CU | MF | Required Lumens (approx) |
|---|---|---|---|---|---|
| 2.0 × 1.5 | Seedlings | 8,000 | 0.65 | 0.85 | 43,478 |
| 3.0 × 2.0 | Vegetative | 20,000 | 0.70 | 0.85 | 201,681 |
| 4.0 × 3.0 | Flowering | 35,000 | 0.65 | 0.80 | 807,692 |
| 1.2 × 1.2 | Herbs | 15,000 | 0.75 | 0.90 | 32,000 |
| 5.0 × 4.0 | Custom | 25,000 | 0.60 | 0.85 | 980,392 |
These are illustrative values. Use your fixture specs and room conditions for best results.
Formula Used
Target illuminance (lux) represents desired light on the plant canopy.
- Area (m²) = length × width (after converting units)
- Required lumens (lm) = (Target lux × Area) ÷ (CU × MF)
- Estimated power (W) = Required lumens ÷ (lm/W)
- Fixture count = ceil(Required lumens ÷ (Fixture W × lm/W))
CU increases with better optics and reflective walls. MF accounts for dust and lamp aging, helping you avoid under-lighting over time.
How to Use This Calculator
- Measure your grow area length and width, then choose units.
- Select a growth stage, or enter a custom lux target.
- Pick a reflectance preset and fine-tune CU if needed.
- Set MF based on cleanliness and maintenance habits.
- Choose a light type and confirm lm/W from your specs.
- Enter fixture wattage to estimate recommended fixture count.
- Press Calculate to view results above the form.
- Use CSV or PDF downloads for planning and records.
Lighting goals for indoor growing zones
Room lighting for gardening is about delivering enough usable light to leaves while keeping heat and power under control. This calculator helps you size light output for shelves, tents, propagation tables, and sunny-window supplement zones by estimating the illuminance you need on the plant canopy.
How the calculator translates area into lumens
The core relationship is straightforward: lux equals lumens per square meter. To estimate required lamp lumens, the calculator multiplies target lux by floor area, then divides by two correction factors: utilization factor (how well the fixture aims light at the crop) and maintenance factor (how much output is lost to dust, aging, and temperature).
Typical lux targets for common plant stages
Data-driven targets vary by crop and environment. As a starting point, low-light herbs and microgreens often perform around 5,000–10,000 lux. Seedlings and cuttings commonly use 8,000–15,000 lux for compact growth. Fruiting plants and high-light greens may benefit from 15,000–30,000 lux when using white grow lights as a supplement, provided temperature and watering are managed.
Choosing fixtures and accounting for real losses
Real rooms reduce delivered light. Dark walls absorb photons, hanging height spreads the beam, and lens or reflector quality changes uniformity. The calculator lets you choose surface reflectance, ceiling height, and fixture efficiency so the estimate reflects these losses. If you know a fixture’s rated lumens, you can also estimate how many fixtures are needed to reach the target in your space.
Practical measuring tips for consistent results
After installation, verify results with a light meter at canopy height and at several points across the growing area. Aim for even readings and adjust spacing before increasing brightness. Recheck after cleaning lenses and when replacing bulbs, because small changes in output can affect stretching, leaf color, and flowering timing. You can trade intensity for hours: 10,000 lux for 16 hours may rival 15,000 lux for 10 hours. Increase levels gradually over days to prevent seedling stress. And watch leaf temperature closely.
FAQs
What is a good lux level for seedlings?
Many seedlings do well around 8,000–15,000 lux at canopy height. Start at the low end for newly germinated trays, then increase as true leaves develop to reduce stretching without overheating.
Why does the calculator ask for utilization and maintenance factors?
They adjust ideal math to real conditions. Utilization reflects how much light reaches plants based on fixture type and layout. Maintenance reflects output loss from dust, aging, and heat, helping prevent under-lighting.
Can I use lumens from a grow light label directly?
Yes, if the label provides lumens for white fixtures. Enter rated lumens to estimate fixture count, but remember optics and mounting height affect delivered lux, so confirm with measurements after installation.
Is lux the same as PPFD for plants?
No. Lux is weighted for human vision, while PPFD measures plant-usable photons. Lux can still guide white-light setups, but if your fixture lists PPFD, use those specs and match crop requirements.
How do reflective walls change the result?
Higher reflectance means more light is bounced back into the canopy area, improving effective delivery. White or reflective surfaces typically reduce the lumens required compared with dark walls or open rooms.
What should I do if readings vary across the growing area?
Improve uniformity by raising the fixture slightly, adding diffusion, or using more fixtures at lower output. Reposition shelves or plants so the lowest-reading zones still meet your minimum target.