So I did a little experiment today. I use the Photone app with their diffuser that I picked up. I had a privacy screen protector on my iPhone and the protector is tinted for obvious reasons. I found when I used the app with the diffuser and screen protector my readings were 50-100 units lower than without the protector. Just something to keep in mind if relying on the app with a privacy screen protector. Have to calculate for the difference.
Are you on the surface of the sun 
Lmao that’s what I’m saying it was at only 60% with a 100 watt spider farm sf1000. They got my money…bastards. I’ve had a couple of people tell me how inaccurate they were. Thankfully @low gave me the proper readings at light intensity and height, well at least a good starting point.
Maybe this will help op
B-Low will steer ya straight 
Wow that’s nuts!
I dowloaded the “ppfd meter” app (home studios) and found my phone sensor was about 50% off the published PAR map readings. That sucked. But the app recommended a uni-t ut383bt (blue tooth) lux meter as it can connect to it via bluetooth and use its sensor. Much closer to the published par map readings now, only about 3% adjustment. Best $31 I’ve spent.
I figured for the fun of it I would do another test with one of the daylight lamps for seasonal depression that I have. I know for fact that it is set at 10k lux. So I used the phone and diffuser and it read dead on at 12” where it was supposed to. Just found it interesting.