An F.S.U. is a little canister unit that helps start a fluorescent tube in an old magnetic ballasted fluorescent fitting. It is a Fluorescent Starter Unit, thus F.S.U. We don't use them now in modern electronically ballasted fluorescent fittings or with L.E.D. tubes.


In the days when unicorns roamed the Serengeti, we had two popular tubes of F.S.U., one was rated at 4 to 65 Watts, the other up to 125 Watts. This referred to the rating of the tubes. 4 to 65 Watts covers a single tube up to 5 feet long, and the other F.S.U. (up to 125 Watts) covers up to 8 foot long tubes.


I had to change some tubes and starters in an old animal sanctuary yesterday. When I came to buy some new F.S.U.s they were rated 4 to 65 Watts or 70 Watts. The 70 Watt version covers the modern 70 Watt 6 foot tubes. 


Now, a Watt is a very small unit of power. Old tungsten car side lights were just 5 Watts. Dashboard indicator lights might have been just 1.2 Watts. Bright headlights 55 Watts.


So why make two F.S.U.s these days just 5 Watts apart? Why not make just one rated 4 to 70 Watts?


Z.