Fluorescent linear lamps have a low pressure mercury electric-discharge source in which a fluorescing coating transforms some of the ultraviolet energy generated by the mercury discharge into light. Fluorescent lamps are manufactured in a variety of shapes (straight- or U-shaped) and types (rapid start and instant start). General service or linear fluorescent lamps are those lamps that satisfy the majority of fluorescent applications, except for some specific lighting applications, such as lamps used in horticulture, cold temperature installations, and others. Common fluorescent lamps include T12 lamps (T12 lamps have a 1.5-inch diameter), T8 lamps (1-inch diameter) and T5 lamps (5/8-inch diameter).
Initial standards for linear fluorescent lamps were enacted by Congress in the Energy Policy Act of 1992, building on standards developed by states. DOE updated the standards in June 2009, and the standards went into effect on July 14, 2012. The efficiency standards vary by type of lamp. The standard for the most common lamp type—4-foot medium bipin, ≤4500K—is 89 lumens per watt. The new standards can be met by 800 Series T8 lamps, which are more efficient than 700 Series T8 lamps. However, 800 Series T8 lamps require significant quantities of three specific rare earth oxides to produce the phosphor coatings, and these rare earth oxides have recently been subject to significant supply constraints. Due to this market disruption, many manufacturers of linear fluorescent lamps applied for and were granted exception relief. The exception relief allows these manufacturers to continue to produce 700 Series T8 lamps for a period of two years.
DOE published a final rule for updated standards in January 2015. For the 4-foot medium bipin, ≤4500K, DOE proposed a minimum of 92.4 lumens per watt, about four percent more efficient than the current standard. According to DOE, for products sold over a 30-year period, the proposed increase would save consumers and businesses over 250 billion kilowatt hours of electricity, between $2-$5.5 billion, and cut CO2 emissions by 160 million metric tons. To put the numbers in perspective, the cumulative electricity savings would be enough to power about 20 million U.S. households for a year and the CO2 savings would equal the annual emissions of over 33 million passenger cars.
Federal standards included an exemption for high color-rendering index (high CRI) fluorescent lamps which has since become a loophole. Several states (Colorado, Vermont, and Washington) have adopted standards for the high-CRI lamps.
Fluorescent lighting accounts for 60–70% of the total lighting electricity consumed by commercial and industrial buildings.