Luxi, the clip-on adapter that turns your iPhone into an incident light meter, is now on general sale to the public. The product was previously available on Kickstarter and up for pre-order but now anybody can get their hands on one.
The attachment, which is made of plastic, fits over the front or rear-facing camera on your iPhone and, by way of an app, takes incident light readings using the camera sensor. It displays results much like a dedicated, professional exposure meter.
As it takes incident light meter readings and not reflected light readings (like a camera’s built-in meter does), the Luxi doesn’t get confused by backlit or high contrast scenes. So it’s handy for film, landscape photography and video, though not much good if you want to meter a studio flash because it only measures continuous light.