T8s

T8s are a class of fluorescent tubes with a nominal diameter of 1 inch. The designation T8 follows the convention for tubular lamps, where the letter represents tubular form and the number indicates the diameter in eighths of an inch. T8s are widely used in commercial, institutional, and industrial lighting.

Design and operation

T8 tubes are linear lamps designed to operate on fluorescent ballasts. Older installations commonly used magnetic ballasts, while modern systems favor electronic ballasts that improve efficiency and quick start. In some retrofit scenarios, ballast-free configurations or direct-wire connections are used for LED replacements. Typical lengths for T8 tubes include 2 feet, 4 feet, and, less commonly, longer variants; 4-foot configurations are the most widespread in office and classroom fixtures. Color temperature options range from warm white to cool daylight, commonly specified in the 2700–6500K range. Luminous efficacy varies with ballast and lamp type but generally falls in the high single to low double digits per-watt, often around 90–110 lm/W in efficient electronic-ballast setups. Lifetimes commonly reach tens of thousands of hours, depending on design and operating conditions.

Comparison and replacement

Compared with older T12 tubes, T8s offer higher efficiency, better color rendering, and a smaller diameter that enables more compact fixtures. They remain in use in many existing lighting systems, particularly in troffers, wraparound fixtures, and similar commercial luminaires. Mercury content requires proper disposal and recycling at end of life. Increasingly, T8 installations are being replaced or retrofitted with LED linear tubes, which may require rewiring or ballast compatibility considerations. See also fluorescent lighting, ballast, and LED retrofit tubes.