If you want to take your photography up a notch without spending big bucks, the $29.95 Luxi attachment for your iPhone can help. It’s a small dome that slides over the front-facing camera in order to turn it into an incident light meter.
Professional photographers likely already have a standalone light meter, which can cost hundreds of dollars, but Luxi gets you started at a fraction of the cost and without having to carry around another bulky device.
Incident light meters work by measuring how much light a subject receives, rather than how much it reflects. Holding the meter up to your subject provides you with suggested camera settings to properly expose the shot.
Luxi, which comes in iPhone 4/4s and iPhone 5/5s, models pairs with an accompanying iPhone app to show you readings. You can also use any other light meter apps that rely on the front camera, but not all of them have been specifically designed with Luxi in mind.
Based on our limited tests, the meter is accurate. If you’re having trouble, you can calibrate the meter to your camera by measuring its readings against your camera’s auto settings and adjusting sliders from within the Luxi app.
Luxi probably isn’t going to replace the dedicated light meters found in serious photographers’ kits, but it’s a convenient accessory that puts the device you already own to work for you.