Light Meter (lux) – measure how sunny a spot really is
"Full sun" on a plant label is relative. A spot that looks bright to you may be too dark for a tomato. The light meter turns your phone into a lux meter and reports the real light level on your bed — in numbers, not by eye.
How a phone measures light
The tool uses the phone camera with a set exposure to estimate light in lux (lux = lumen per square metre). Point the phone at the bed surface and the reading shows how bright the spot is at that time of day.
Note for iPhone and Mac
The measurement needs manual camera-exposure control, which Apple devices (iPhone, iPad, Safari on Mac) do not expose. On those devices the meter is unavailable — it works on Android and in browsers with camera access.
How much light vegetables need
Rough daylight thresholds help match a plant to a spot:
| Exposure | Light level | Example vegetables |
|---|---|---|
| Full sun | > 30,000 lux | tomato, pepper, cucumber, squash |
| Partial shade | 10,000–30,000 lux | lettuce, spinach, arugula, chard |
| Shade | < 10,000 lux | shade herbs, parsley, chives |
Putting the reading to use
- measure the same spot at different times — light shifts as the sun moves
- check the spot in spring and summer — leafed-out trees change the result a lot
- sun-lovers in too dark a spot get leggy and yield less
For growing under artificial light, see the grow-light calculator, which converts lamp power to DLI.
Frequently asked questions
Is a phone lux reading accurate?
It is an estimate, not a lab measurement — accuracy depends on the camera and calibration. For a practical "sun / partial shade / shade" call it is plenty.
Why does the meter not work on iPhone?
The measurement needs manual camera-exposure control, which iOS and Safari do not expose. It works on Android and in browsers with camera access.
How many lux is full sun?
In garden terms, above roughly 30,000 lux in full daylight is full sun, 10,000–30,000 lux is partial shade, and below that is shade.
What time of day should I measure?
Ideally several times — morning, midday and afternoon — because the sun moves, and a spot sunny in the morning may be shaded by afternoon.
Light Meter (lux) – measure how sunny a spot really is
Every tool runs in your browser and in the mobile app — free, no sign-up, works offline too.
Open this tool in the app →