Light Meter for Plants: PPFD

Light Meter for Plants turns your phone into a light meter for plants. Hold it where the leaves are and see how much light that spot gets in lux or foot-candles, with an estimated PPFD and DLI for the kind of light you have: sunlight, white LED, full-spectrum LED, fluorescent or HPS.

Then see which plants suit that spot, save each sill and shelf you measure, and check them again as the seasons change. It works without internet and needs no account.

WHAT YOU GET
• Live reading in lux or foot-candles, with estimated PPFD (µmol/m²/s) and DLI (mol/m²/day)
• Light source choice, so PPFD uses a factor that fits your light
• Day length setting for the DLI (12 hours for daylight, 16 for grow lights, or your own)
• Light level at a glance: too dark, low, medium, bright indirect or direct, with what it means for plants
• Hold button to freeze the value, steady or fast smoothing, and the screen stays on while you measure
• Positioning guide: where the light sensor sits and how to hold your phone
• Plant library with more than 100 common houseplants: search by common or scientific name, filter by light level, see each plant's light needs and a short care note
• "Check this spot now" tells you whether a plant would find the light ideal, tolerable, too dark or too bright
• Save up to 5 spots (rooms, window sills, shelves) with their measurement history and the plants that fit there
• Camera estimate for phones without a light sensor
• Dark theme, tablet layout and screen reader support

PREMIUM
• Daily log with charts: the brightest light and average PPFD per day and an estimated DLI, over 7, 30 or 90 days
• Grow-light mode: pick seedlings, leafy greens, vegetative or flowering, see whether the PPFD is below, in or above the target range, and get advice to raise or lower the lamp or change the dimmer. Without Premium, you can watch a short ad to use it for up to an hour.
• Calibration: enter what a reference meter shows at the same spot, and every reading is corrected from then on
• Unlimited spots and no ads
Premium is a one-time purchase.

WHO IT IS FOR
• Houseplant owners: find the right window for a plant you just bought, or learn why one is stretching toward the glass.
• Hydroponics growers: check the light over every tray and keep an eye on the daily light your crops get.
• Grow light users: set the lamp height and dimmer for each growth stage and compare spots under the light.

QUESTIONS
How accurate is it?
Every reading is an estimate. Phone light sensors vary by maker and model, so two phones can show different values at the same spot. PPFD is worked out from lux with a factor per light source, and DLI from PPFD and your day length. For exact values, calibrate with a reference meter (Premium).

Why does the reading stop at a high value?
Many phone sensors have a limit, often somewhere between 10,000 and 40,000 lux. In strong sun the app tells you when the sensor may be at its limit.

My phone has no light sensor. Can I still use the light meter for plants?
Yes. The app then offers a camera estimate: point the back camera at where the light comes from, with a sheet of white paper in front of it. It is less accurate than a sensor and is labelled that way. Camera frames are processed on your phone and are never saved or sent.

Which phones does it work on?
Android phones and tablets with Android 8.0 or newer. Most phones have a light sensor near the front camera. Tablets and phones without one use the camera estimate.

Does it work offline?
Yes. Measuring, the plant library and your spots need no internet. A connection is used only for ads and purchases.

What does Premium add?
The daily log and charts, grow-light mode, calibration, unlimited spots and no ads.

What about privacy?
No account and no sign-in. Your spots and measurements stay on your phone.

Light Meter for Plants gives estimates to help you place your plants. Phone sensors vary, so calibrate with a reference meter when you need exact values.

Recent changes:
First release of Light Meter for Plants. Measure the light where your plants grow in lux or foot-candles, with an estimated PPFD and DLI for sunlight or grow lights, check which of more than 100 houseplants suit each spot, and save up to 5 spots. Phones without a light sensor get a camera estimate. Premium adds the daily log with charts, grow-light mode, calibration, unlimited spots and no ads.