Cross calibrating to a reference sensor is a routine task for people who build loggers, but there are surprisingly few tutorials on YouTube that describe the process of deriving constants for an empirical fit equation with Excel. Especially ones that describe this process with messy 'real world' data.

So here's a quick walk through comparing timing data from a the photo discharge of a reverse bias LED to the Bh1750 Lux sensor.  The error on this run was too high to be practically useable, but this kind of exercise is just the starting point to refine the physical system. We will make a post on all the gory details of that process later.