Our eyes are poor light meters. UF/IFAS points out that a desk by a window can be ten times brighter than a workspace across the hall that looks only slightly darker. Three simple tools help.
The shadow test costs nothing. On a bright day, hold your hand or an object above the spot where the plant sits. A sharp, well-defined shadow suggests bright light; a soft, blurred shadow suggests medium light; little or no shadow means low light.
A phone light-meter app gives you a number. Phone sensors are not precise, but they are usually good enough to compare one spot with another, which is mostly what you need. A handheld light meter is more reliable if you want to go further.
Readings come in lux or foot-candles; one foot-candle is roughly 10.8 lux. Sources draw the boundaries differently, so treat any figures as rough bands. UF/IFAS, for example, calls 25–100 foot-candles low light, 100–500 medium, 500–1,000 high and over 1,000 direct sun. Measure at different times of day, and again in another season, because light changes.
Key points
- Shadow test: sharp means bright, blurred means medium, faint or none means low.
- Phone apps are imprecise but good for comparing spots.
- Treat light figures as rough bands; sources differ.
Try this
Do the shadow test at three places where plants sit or might sit, and note which is brightest.
Check yourself
Read more in the reference
Sources
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