Introduction In 2008@ Congress began the rulemaking process for fluorescent ballasts as required by the Energy Independence and Security Act (EISA) 2007. The rule in effect in 2008 only covered the federally regulated T12 lamp ballasts for 4-foot and 8-foot T12 lamps@ and ballast efficiency factor (BEF) was the performance metric. As BEF was a system parameter@ many factors in the lamp load and photometric measurement system contributed to a wide error range. This error range did not allow the accurate measurement of the small differences in today??s high performance electronic ballast. As a result@ a new metric was developed@ ballast luminous efficiency (BLE)@ based solely on electrical measurements. The test plan for the BLE metric measurement is based on the ballast operating a lamp load@ and the total arc power of all the lamps is summed and applied to an equation. The equation coefficients are selected based on the ballast type@ and the equation then provides the minimum efficiency for the ballast under test. The ballast efficiency is calculated (or directly measured) by dividing the sum of the total arc power by the input power. The calculated ballast efficiency is then compared to the BLE limit from the equation. If the efficiency of the ballast is equal to or greater than the BLE limit@ then the ballast is compliant. The rule became effective January 13@ 2012@ and required compliance by November 14@ 2014. In this rule@ all ballast types are covered@ including T12@ T8@ T5@ and sign and residential ballasts. The rule includes an exception for dimming ballasts@ Electromagnetic ballasts for electromagnetic interference (EMI)-sensitive areas@ and program start ballasts with discharge currents below 140 mA. The rule also brought certain changes to increase the accuracy of existing T12 BEF system measurements until compliance was required under the new rule. These changes include tighter tolerance on reference lamps@ specification of fixed voltage reference method for photometrics@ and tighter tolerance on laboratory temperature control. Under this rule@ BLE is the performance metric@ but many luminaire designers depend on the old BEF parameter. In order to provide a BEF number@ the BEF may be calculated by first determining the ballast factor (BF)@ then dividing the BF by the input wattage as was done previously. The change comes with the determination of BF. The new way to determine BF is to take the average of the discharge power and divide by the rated discharge power as stated in ANSI C78.81-2010??no longer a photometric measurement. Note that BEF can only be calculated as stated. Existing BEF numbers cannot be back calculated to arrive at input wattage or BF.