An examination of the similarities and differences between ASHRAE/IES 90.1 and IECC 2018. Specifically, as it relates to Section C405 and electric lighting systems. We will address exterior and interior lighting, interior lighting power, dwelling units, multiple-building facilities or campuses, lighting in speculative and shell buildings, garages, and parking areas. From IECC 2018, Section C405.2 – we will address Mandatory Lighting Controls and the two methods that comply with this section. This section will also address time-switch controls, light-reduction controls, daylight-responsive controls, and manual controls.