The little Luxi turns your iPhone’s front camera into a light meter. A what? A light meter, a device that measures the amount of light falling on a subject so that you can set the exposure correctly on your camera.
But wait, doesn’t you camera already set its own exposure? Doesn’t it have a light meter built in for when i want to kick it old school in manual mode? Yes and yes, but this $30 widget might still be handy.