Luxi is a clip-on device turns your iPhone into an incident light meter, and sends readings to the corresponding app.
Like many other niche photo products today, Luxi was brought to market via Kickstarter, where the campaign raised over $100,000 for the $30 iPhone accessory (For a little perspective, I was looking at iPhone cases earlier today that cost $35 . . . I didn’t buy one).
Luxi is compatible with the iPhone 5 and iPhone 4/4S. It also works with any light meter app that can use the front-facing camera, and can be calibrated with an offset. You can find out more about Luxi here on Bite My Apple’s website.