How to turn your iPhone into a photographic light meter
Using an iPhone for a photography light meter is not difficult at all with Luxi Light Meter.
After purchasing the Luxi For All light meter dome (on Amazon or www.LuxiForAll.com) and downloading the FREE app in the Apple App Store, it is just a matter of seconds to get accurate light meter readings on your iPhone.
Step 1 - Attach Luxi to your iPhone covering the front facing camera with the white dome.
Step 2 - Open the Luxi app.
At this point, you should see a screen that has calibration sliders, EV readings and a large “HOLD” display.
Step 3 - Position the phone in front of your photographic subject.
Step 4 - Press on the word, “HOLD.” This will lock in the light at that moment and render a recommended F-Stop and speed.
The word “HOLD” will change to “HELD” to indicate that you have locked in the setting.
Because Luxi is conveniently small, keep the Luxi dome in the cloth bag that comes with it. This helps protect the plastic dome from scratches and makes it easy to find in your gear bag.