For professional photographers, an incident light meter is rather important. Unlike a reflective light meter, which measures the amount of light bouncing off a subject, an incident light meter measures light before it reaches the subject. This is helpful in situations where lighting is inconsistent. A new product called Luxi is designed to turn your iPhone into just such a light meter.
Luxi, when placed over the iPhone's front-facing camera, is able to detect the amount of light falling onto the subject of the photo. The creators claim that it can be used with any light meter application that supports the iPhone's front-facing camera. A deal is in the works to add a Luxi-specific mode to the iOS Pocket Light Meter app.
The difference between Luxi and a light reader that only uses the camera is that it captures light from a 180-degree angle, which, in theory, should help photographers get a more accurate reading of the light in a scene. The creators compared the results of Luxi with a Sekonic L-308 handheld light meter, and they were exactly the same.
Funding for the Luxi is underway on Kickstarter. The creators currently have over double the US$10,000 goal from backers. The device is available for both the iPhone 5 and iPhone 4/4S, with a minimum pledge of $17 for the early bird special. Once those dry up, a $19 pledge is required. Luxi will have a final retail cost of $24.95 when it ships in April.
The Kickstarter pitch below introduces Luxi and provides more information.