I have a few light meters, a couple of digitals and a couple of old selenium cell meters that still work even after so many decades of use. My favorite is the Sekonic Flashmate L-308S, a small and handy meter that reads both incident and reflected light. It always comes with me whenever I shoot with my meterless film cameras. It is also used in the studio for multiple flash reading.
I heard there are a few light meter apps for the iPhone so I downloaded one just in case I forget my regular light meter. My iPhone is always with me so I thought adding a light meter app to this very multi functional digital version of a Swiss army knife would come handy. After I downloaded the app I tested it with my digital camera and the exposure was accurate. It works like a spot meter. You take a reflected light reading by pointing the iPhone camera lens to your subject. Recently I finally get to use it with my Leica M4-P and I was very happy with the results. Below are a few pictures taken with a roll of Kodak BW 400CN film with very minor adjustment of curves in Photoshop.
Not bad for a free app, the only thing I have to deal with are the ads that came with it which can be removed by upgrading to the paid version. Also when I use it to make light readings of people in the streets they usually think I'm taking a picture of them with my iPhone.