Luxi is a new, small diffusion dome that fits over your iPhone’s front-facing camera. When attached and used with a light meter app, it can help you determine the best settings for your DSLR or other camera.
Incident light meters, like Luxi, measure the amount of light falling on the subject you are photographing, not the light reflected by the subject. Their readings are independent of the subject’s reflectance and can’t be “fooled” by tricky lighting situations like back-lit subjects (e.g. sunset portraits).
The Luxi is available for the iPhone 4/4S and 5. It retails for US$24.95 and is available online at www.esdevices.com.