The phrase "complete blackout" means that there is a total loss of electricity or a complete absence of lights, causing total darkness. Full definition
The 40 seater conference room features large windows and has an abundance of natural light (with complete blackout facility). (sa-venues.com)
Custom motorized blinds are available as roller blinds, roman blinds and panel blinds and if complete blackout required — a cassette system can be installed — using a contemporary blackout fabric. (housecouturier.eu)
2: Complete blackout of front and side glass surround on the Saab contrasts with chrome outline and simple pillar blackout on the S60. (automobilemag.com)