Why Measurement Matters
Plant care guides often categorise light as "bright indirect," "low light," or "full sun." These categories correspond to measurable lux ranges. Without a reading, it is difficult to know whether a given east window actually falls into the range a plant needs, especially in Poland where sun angles differ markedly between December and June.
A simple measurement session takes about 15 minutes and gives you a reliable baseline to work from. You do not need specialist equipment — a smartphone with a light meter app is sufficient for practical purposes.
What to Measure: Lux and Foot-Candles
Light intensity for plant purposes is usually expressed in lux (the SI unit) or foot-candles (used in older American horticultural guides). One foot-candle equals approximately 10.76 lux. Most smartphone apps report in lux.
As a general orientation:
- Below 500 lux: dim indoor light, suitable for shade-tolerant plants
- 500–2,000 lux: moderate indirect light
- 2,000–10,000 lux: bright indirect or brief direct sun
- Above 10,000 lux: direct sunlight at the window glass
These ranges are widely used in horticultural literature; the specific thresholds for individual species vary and should be checked per plant.
Tools You Can Use
A basic digital lux meter, available from electronics suppliers for a modest price, gives reliable readings for this purpose. Smartphone apps using the front camera can produce reasonably consistent comparative readings, though they are less accurate than dedicated meters. For practical plant placement decisions, either approach is adequate.
Calibrated lux meters designed for horticultural use are available from suppliers in Poland. Basic models suffice for indoor plant measurement; laboratory-grade instruments are not necessary.
When to Take Readings at an East Window in Poland
The timing of direct sun at an east-facing window depends on the time of year and your latitude. In Warsaw (approximately 52°N), sunrise occurs around 04:15 in late June and around 07:45 in late December. The window receives its peak direct sun in the first one to three hours after sunrise.
To capture the full picture, take readings at three times:
- Within the first hour after sunrise (peak direct sun period)
- Two hours after sunrise (transition from direct to indirect)
- Midday (indirect ambient light only at an east window)
Repeat this in two seasons — summer and winter — to understand seasonal variation. The difference can be substantial.
How to Position the Meter
Hold the sensor or phone at the location where the plant will actually sit, with the sensor facing upward toward the light source. Avoid blocking the light with your own body. Take readings at several depths into the room — immediately at the glass, 50 cm back, and 1 m back — to understand how quickly the light drops off.
Note which way the window faces precisely. A window described as "east-facing" may be northeast or southeast, which shifts the sun entry time by 30–60 minutes and changes the intensity at peak.
Recording and Using Your Data
A simple table with date, time, sky condition, and lux value is enough. After a few readings you will have a clear picture of the light envelope at your window. Use this to match plants to the light available, rather than relying on general category labels alone.
For plant selection based on these measurements, see the dedicated article. For how the same readings affect a reading workspace setup, see the workspace article.