Ballast efficiency is the reference lamp power divided by the ballast input power when tested according to ANSI C82.6-2015.
The ratio of the output wattage to the input wattage is at 100 percent tubing load.
EXCEPTION to Section 140.8(b)5: Single voltage external power supplies that are designed to convert 120 volt AC input into lower voltage DC or AC output, and have a nameplate output power less than or equal to 250 watts, shall comply with the applicable requirements of the Appliance Efficiency Regulations (Title 20).