One ballast for 1 lamp T5: 1X21W, 1X28W, 1X35W; T8: 1X15W, 1X18W, 1X36W, 1X58W; T12: 1X20W, 1X40WOne ballast for 2 lampsT5: 2X21W, 2X28W, 2X35W; T8: 2X15W, 2X18W, 2X36W, 2X58W; T12: 2X20W, 2X40W1. High power factor, Low harmonic. Low wave peak radio. Suitable for group installation. 2. Abnormity...