It doesn't replace an incident meter or a flash meter or a 1-deg. spot meter, but it's pretty handy, and if you always carry your iPhone, then it's the meter you've always got with you, which makes it a pretty good replacement for a pocket meter like, say, the Digisix. The Digisix takes incident or wide beam reflected readings like a center-weighted averaging meter and can give the ambient temperature, which is useful for peel-apart instant films. The "Light Meter" app is around a 10-deg spot meter and is slower to react than a normal light meter, which one can learn to work with, plus an iPhone can do a lot of other useful things like give sunrise/set, run The Photographer's Ephemeris, perform various useful photographic calculations, measure tilt and swing angles, serve as a compass and level, map, internet, timer and even a dedicated photo processing timer, records voice, typed, and handwritten notes, and even makes phone calls.