I recently installed this free app onto my android: https://play.google.com/store/apps/details?id=com.homestudio.ppfdmeter&hl=en_US&gl=US

Seems to respond appropriately to light. While I am sure this is not dead nuts accurate considering free app and standard light sensors on phone, I would love to know how close it is to a real meter. Can anyone with a real meter do a rough comparison? Thanks in advance. Steve