Footcandle to Lux Converter Calculator

Example Data Table

Values are approximate and depend on placement, season, and shading.

Why illuminance matters for plant placement

Indoor growers often judge brightness by eye, but plants respond to measurable light. Illuminance helps you compare spots across a room, between shelves, and under different fixtures. A consistent approach reduces guesswork when rotating trays, raising lamps, or choosing reflective surfaces. This converter lets you normalize readings from meters that report either footcandles or lux.

Understanding footcandles and lux in practice

Lux measures lumens per square meter, while footcandles measure lumens per square foot. The same light level produces different numbers because the units use different areas. Converting supports mixed equipment, older gardening guides, and supplier charts. It also helps when you track seasonal changes, because winter window lux can fall quickly compared with summer conditions.

Reading technique that improves repeatability

Take readings at canopy height and aim the sensor toward the light source, unless your meter specifies cosine correction. Measure several points across the growing area, then average them to represent what the plant actually receives. Record distance from lamp, dimmer setting, and any shade cloth. Small adjustments can change results more than the conversion factor.

Interpreting results with garden-friendly bands

The light band shown after conversion is a quick reference. Low light suits shade tolerant foliage; medium light supports many houseplants; high light works for herbs and vigorous greens near bright windows; very high light aligns with strong LEDs and greenhouses. Treat bands as starting points and watch leaf color, stretch, and scorch for feedback.

Using exports for planning and troubleshooting

Download the CSV to build a simple log for each shelf or room, then compare changes after cleaning lenses, adding reflectors, or moving fixtures. The PDF report is useful for sharing measurements with a grow team or documenting conditions before and after upgrades. If you also record photoperiod hours, you can relate illuminance to day-to-day routines, making it easier to spot timer failures, aging diodes, or shifting window sun angles. Consistent records help you improve uniformity and reduce weak, uneven growth.

FAQs

1) What is the exact conversion factor?

One footcandle equals 10.7639 lux, based on the area difference between one square foot and one square meter. The calculator applies this factor in both directions.

2) Do lux or footcandles measure plant light quality?

They measure brightness weighted to human vision, not plant photon output. Use them for comparing locations and consistency, then adjust based on plant response or dedicated PAR measurements when available.

3) Where should I place the light meter sensor?

Place the sensor at leaf canopy height and sample multiple points across the growing area. Average the readings to represent what the plant receives, especially under LEDs or window light.

4) Why do my readings change during the day?

Sun angle, cloud cover, and indoor shading shift rapidly, so window lux can swing widely. Artificial lighting is steadier, but distance, dimmer settings, and dirty lenses can still alter results.

5) Can I use this for greenhouse lighting audits?

Yes, for relative comparisons and documenting changes after maintenance. For crop-specific targets, combine these readings with photoperiod notes and, when possible, PPFD or DLI measurements.

6) What do the light bands mean?

Bands provide quick context: low, medium, high, very high, and extreme. They are guidelines only; leaf color, stretch, and scorch offer better feedback for fine tuning placement and duration.