How accurate is this light meter?

It is an estimate, not a calibrated instrument. A phone or webcam sensor was built for pictures, not photometry, and most browsers do not expose the camera's real exposure settings, which forces a rough brightness-only fallback with roughly plus or minus 50 percent error. When exposure settings are available the estimate is tighter, roughly plus or minus 30 percent, but still not lab grade. Calibrate the Calibration option against a light source of known brightness (another meter, or a lamp's spec sheet) to improve the rough estimate for your specific camera.

Why does the reading change when I move the camera or my hand?

Your camera runs auto exposure and auto white balance continuously, so pointing it at a brighter area, a shadow, or a strongly colored surface changes what the sensor reports even if the room light has not changed. Hold the camera steady on the surface you actually want to measure, give it a second to settle, and read the smoothed value rather than any single instantaneous spike.

Is my camera video uploaded anywhere?

No. The video stream never leaves your device. Every frame is sampled and averaged locally in the page, the resulting numbers are what get analyzed, and nothing is recorded, saved, or sent to a server. Closing the tab or pressing Stop ends the camera stream immediately.

Light Meter: free, private, in your browser

Frames are sampled and averaged in this tab, then discarded. Your files and inputs never leave your device.

Point your camera at the light you want to measure. The camera only turns on when you press Start, and it stops when you leave.

Calibration 1.00x

Point this page and a real light meter at the same light, type what the meter says, and the factor that makes the two agree is applied to every later brightness only reading. It is saved on this device as a preference, never a reading and never a frame.

Known reading (lux)

Read a photo instead

Drop a photo here for a one shot reading, or click to choose one. The camera that took it already picked its own exposure and tone curve, so a photo reads as relative brightness rather than an absolute level, and it stops the live camera while it is shown.

Press Start camera or drop a photo to see the full report, including the formula and its caveats.

Related tools

What it does

Turns your camera into a rough light meter. It reads the average brightness and color of the live preview and estimates illuminance in lux (or footcandles) along with a correlated color temperature in Kelvin. When your browser exposes the camera's exposure time, ISO, and aperture it uses the same incident-light formula a handheld meter uses; otherwise it falls back to a brightness-only estimate you can calibrate against a known light source.

How to use it

Press Start above to turn on your camera and point it at the light you want to measure. The lux reading, its confidence, and the estimated color temperature update live from a smoothed average of recent frames. If the reading looks off, adjust the Calibration option while pointed at a light source of known brightness until it matches.

Why this one

Dedicated lux meter apps are usually locked behind an app store install, an account, or ads, and most never explain how the number was actually computed. This page runs the same computation in the open, entirely in your browser: the camera stream is analyzed on this page and discarded, nothing is recorded or uploaded, and the exact formula is shown in the results.

FAQ

How accurate is this light meter?: It is an estimate, not a calibrated instrument. A phone or webcam sensor was built for pictures, not photometry, and most browsers do not expose the camera's real exposure settings, which forces a rough brightness-only fallback with roughly plus or minus 50 percent error. When exposure settings are available the estimate is tighter, roughly plus or minus 30 percent, but still not lab grade. Calibrate the Calibration option against a light source of known brightness (another meter, or a lamp's spec sheet) to improve the rough estimate for your specific camera.
Why does the reading change when I move the camera or my hand?: Your camera runs auto exposure and auto white balance continuously, so pointing it at a brighter area, a shadow, or a strongly colored surface changes what the sensor reports even if the room light has not changed. Hold the camera steady on the surface you actually want to measure, give it a second to settle, and read the smoothed value rather than any single instantaneous spike.
Is my camera video uploaded anywhere?: No. The video stream never leaves your device. Every frame is sampled and averaged locally in the page, the resulting numbers are what get analyzed, and nothing is recorded, saved, or sent to a server. Closing the tab or pressing Stop ends the camera stream immediately.

Keyboard shortcuts: press ? anywhere on this page to see them.