Light Meter for Photography
Incident vs. reflected metering, EV, and exposure basics
Correct exposure comes down to three settings working together — aperture, shutter speed, and ISO — and a light meter's job is to measure the light in a scene and translate it into a valid combination of the three. Camera phones and digital cameras with live preview screens do this automatically and show you the result before you shoot; film and manual cameras don't, which is exactly why a dedicated meter still matters to analog and manual shooters.
There are two fundamentally different ways to meter light. Reflected-light metering — what a phone-based meter and a camera's built-in meter both do — measures the light bouncing off your subject, which means it can be fooled by very bright or very dark subjects (a meter reading a white wall and a black wall in the same light will suggest different exposures, even though the light itself hasn't changed). Incident metering measures the light actually falling on the scene, typically using a diffusing dome held near the subject pointed at the light source, and isn't affected by subject color at all — it's the more accurate method but needs a meter built for it. A phone-camera-based meter reads reflected light.
Exposure value (EV) is a standardized way to express a given light level independent of any specific aperture/shutter pairing — it lets you compare exposures or scenes on a single number instead of a table of settings. We built Luxmo for film and analog shooters who want a fast, dependable reflected-light reading on their phone without digging out a separate handheld meter for every shot.
The app
How it compares to other tools
Frequently asked questions
What's the difference between reflected and incident light metering?
Reflected metering measures light bouncing off the subject and can be thrown off by very light or dark subjects, since it's really measuring brightness, not illumination. Incident metering measures light falling directly onto the scene, usually with a diffusing dome, and gives a subject-independent reading — it's the more accurate method for controlled exposure but requires a meter designed for it. Phone-based light meters, including camera apps, read reflected light.
What is EV (exposure value)?
EV is a single number that represents a given amount of light, independent of which specific aperture and shutter-speed combination you use to capture it — EV 10 can be achieved at f/2.8 and 1/60s, or f/8 and 1/8s, among other pairings, all letting in the same total light. It's a standardized way to describe or compare light levels across scenes and cameras.
Why do film and analog photographers need a separate light meter?
Digital cameras (including phones) can preview the exposure on screen before you shoot, effectively acting as their own meter. Film and fully manual cameras have no such preview — you have to know the correct exposure before pressing the shutter, which is what a dedicated meter is for. It matters even more with film because mistakes aren't visible until after developing.
What is the "sunny 16" rule?
It's a rule of thumb for setting exposure without a meter: on a bright, sunny day, set your aperture to f/16 and your shutter speed to roughly the reciprocal of your ISO (e.g. 1/100s at ISO 100). It's a useful backup or sanity check, not a replacement for metering in anything other than direct sunlight.