Light Meter: Exposure & Lux

Light Meter turns your phone's rear camera into an exposure meter for film, digital and cine, and a lux and PPFD meter for plants and grow lights. It shows a number only once the reading has settled, and when it cannot measure, it tells you why.

Plenty of light meter apps freeze, show a black screen or give no reading at all, and many of the rest want a subscription. This one reads the exposure the camera settles on, converts it to EV at ISO 100, and adds back the part the camera could not reach in a dark room. When a scene is too dark or too bright to measure, the status reads TOO DARK or TOO BRIGHT instead of printing a guess.

THREE METERING MODES
Reflected meters the whole frame, the way a camera's own meter does.
Incident is cosine-corrected in software, so you hold the phone at your subject, facing the camera position, with no diffuser dome.
Spot measures a small rectangle you drag over the subject and prints its angle of view in degrees, so you know exactly how wide the spot meter is reading.

EXPOSURE, SOLVED
Fix any two of aperture, shutter speed and ISO and the light meter solves the third, in full, half or third stops. Choose your film stock and it adds reciprocity failure correction for long exposures, shown as a separate number so you can see what was added. For video, the 180° shutter mode pins the shutter to your frame rate and solves the aperture instead.

GROW LIGHTS AND PLANTS
Grow mode reads lux and converts it to PPFD and DLI for sunlight, white LED, red and blue LED, fluorescent, metal halide, sodium and incandescent light. A short note says which plants that light level suits. Set the photoperiod and the daily light integral follows.

ROLLS AND CALIBRATION
Log a reading to the roll you are shooting with a note for the frame, then export the roll as CSV. If you own a handheld light meter you trust, match the app to it once with a calibration offset in sixths of a stop.

WHAT IS FREE
Reflected metering in full stops, with EV, lux and foot-candles, is free and stays free. Incident and spot metering, half and third stops, choosing what to solve for, reciprocity correction, the cine shutter, calibration, rolls and CSV export, and PPFD and DLI come with one purchase, made once. There is no subscription and there are no ads.

PRIVACY
Light Meter uses the camera only to measure light. Nothing is recorded, and no image leaves your phone.