I am the Operations Manager at Extrasensory Devices, the manufacturer of the Luxi light meter attachment for smartphones. I just wanted to chime in to say that you should always be sure to calibrate any light metering app you might be using with Luxi. As Adam points out, there can be slight differences between Luxi attachments--but there can also be small differences in sensitivity between any two smartphones, as well. Manufacturing is never a perfect science, and tiny aberrations from design specs are often seen. These tiny differences can actually make a big difference in the actual amount of light being measured, so calibration is key. By the way, here is a link to our User's Guide, which ought to give you a good idea of how our product works. Finally, if you have any questions about Luxi For All, feel free to ask away!
