Holy Light by Samy Dindane is a plugin for Macs that changes the
background variable based on the amount of ambient light recorded by Mac's light sensor.
The sensor is interrogated using a binary program, the source of which can be found here: holylight-checker.mm. The program works by connecting to Apple's LMU I/O service (
AppleLMUController), and then grabbing the current brightness value. If the value is less than a threshold (1000000) then the background is switched to
'background' value can be set manually with
:set background=light and
:set background=dark (
:help 'background', abbreviation:
bg). Vim tries to pick colours that will look good on a dark/light background.