Photone app is really accurate. Add 3% to PPFD 800 and above though. And use the diffuser. Not sure if they make it for android now? I believe it used to be iOS only awhile back.
Edit - they do have it for android and android version doesn’t require a diffuser. Not sure how accurate it is on Android but tests with the iOS version against apogee meters are really good.
Edit - they do have it for android and android version doesn’t require a diffuser. Not sure how accurate it is on Android but tests with the iOS version against apogee meters are really good.