Brightness looking at the sunny day outside my office: about 1050 lumens.
Brightness at my desk, away from the window, ambient light only: also about 1050 lumens.
I'm no scientist (actually, I am), but should something lit with direct sunlight be brighter than the thing lit indirectly from that?
My guess is the meter only measures ambient light, but uses the BACK camera, and shows an image, making you think the are measuring the light from far away. No, its the local light, just how much actually reaches you.
The app would actually slightly useful, if they used the FRONT camera. Then, i could place it in a location (like my desk), and see how much light there is.
In the current configuration, the sensor is on the back of the phone, and you read it from the front. Kinda silly.