The primary difference between Lepton and Lepton 3 is the improved resolution of the infrared sensor. Lepton provides an output of 80×60 pixels whereas Lepton 3 outputs 160×120.
Despite having four times the number of pixels, Lepton 3 maintains the form factor of its predecessor and actually consumes slightly less power (nominally 140 mW versus 150 mW). A key enabler for the improved resolution is reduction of pixel pitch from 17 to 12 microns.
To learn more, click the thumbnail to the Application Note PDF for a comprehensive comparison of the two cameras