PlantLux.
The SI unit of illuminance, equal to one lumen per square metre and weighted to the sensitivity of the human eye.
What it means for your plants
Lux is useful for comparing spots: low light is about 500–2,500 lux, medium 2,500–10,000 and bright indirect 10,000–20,000. Plants respond to photosynthetic photons (PPFD) accumulated over the day (DLI), so take readings at leaf height around midday and repeat them.
IN PRACTICE
A light meter reads 12,000 lux on a windowsill and 800 lux on a bookshelf 3 m away.
Put it into practice
Lux readings help only if you take them the same way every time. Learn where to hold the sensor, what the numbers mean for plants, and the limits of phone meters.
How to use a plant light meter: lux readings that mean something
