Footcandle: Lux Light Meter

See how much light a spot really gets, in lux and foot-candles, using your iPhone's camera. Free to measure. No battery, no trial tricks, no ads. Pro is a one-time purchase. THREE WAYS TO MEASURE • Flat: lay your phone face up and cover the front camera with one sheet of plain printer paper. Best for window sills, desks and plant shelves. • Card: point the back camera at a sheet of white paper lying where you want to measure. No accessory needed. • Quick: no paper, a rough reading in a second. Each method shows a short guide before your first reading, never a popup over the number. HONEST NUMBERS • Estimates from your iPhone's camera. Calibrate with one tap if you have a meter. • Calibrate your own paper: measure the same spot with Card, then Flat. • "Steady" tells you when the reading has settled. Hold keeps the number after you pick the phone up, with an optional beep. • Too dark or too bright for the camera? Footcandle says "below range" or "above range" instead of inventing a number. • Purple grow lights can't be converted to PPFD with a phone camera, so Footcandle says so. FOR PLANTS AND GROW LIGHTS • Foot-candles with houseplant light levels from university extension services. • PPFD and daily light integral (DLI) estimates for sunlight, white LED, fluorescent, HPS, metal halide and ceramic metal halide, all free. • Pro: DLI logger for a whole day, saved places with history and charts. FOR DESKS, ROOMS, BEDROOMS AND LIGHT BOXES • Reference levels for reading, computer work and detailed tasks. • Evening light guide for winding down, light therapy box check against 10,000 lux. • Pro: room surveys on a 2x2 to 5x5 grid with average, minimum and uniformity, exported as a PDF. FOR PHOTOGRAPHERS • EV, aperture, shutter and ISO from the scene or incident light, ND filter compensation, 1/3 or 1/2 stops, f/0.95 to f/64, ISO 0.8 to 25,600. • Pro: spot metering, two locks, and a log. PRIVATE BY DESIGN • No account, no server, no ads, no tracking. Works in Airplane mode. • Camera frames are analysed in memory and never saved or sent. • Export your readings as CSV any time, for free. Footcandle Pro is a one-time purchase with Family Sharing: unlimited places and history, DLI logger, room surveys with PDF, more calibration profiles, Photo spot meter and two locks, Sun check and iCloud sync. Measuring stays free forever. Footcandle is not a certified light meter and is not for workplace safety compliance.