Bi-pin is the most common and for straight tubes there are just two versions. See Figure 5.6.

Figure 5.6. Bi-pin lamp caps.

Single contact caps are used for Slimline tubes which have a special starting circuit. Four pin caps are used on Mod-U-Line and Circline lamps.

Figure 5.7. Other fluorescent lamp caps.

Fluorescent lamp design is called HOT CATHODE, and requires a second or so before the lamp lights.  To provide the initial warm-up there is a device called a STARTER, which first connects the cathodes in series to allow preheating, and then switches the voltage across the two electrodes. The most common form of Starter is a small cylindrical component containing a glow switch.

All hot cathode lamps have bi-pin or four-pin caps.

Instant start circuits used to be a popular way to give quicker starting with no initial flickering. However, electronic starting methods are now replacing such control gear because they are more efficient and incorporate additional safety features.

The SLIMLINE lamp does not preheat the cathodes and requires special control gear from America, which has no starter. SLIMLINE has single pin caps. SLIMLINE lamps cannot be used on starter or instant start circuits.

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