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.

Fluorescent Lamp Circuit Operation

Figure 5.8 shows the basic fluorescent lamp circuit. The circuit must contain a ballast to limit the current and a starter to provide the pre-heat conditions. Initially the starter switch closes so the two cathodes are connected in series. Current flows and the cathodes heat up emitting electrons. After a short time the starter switch opens so voltage is applied across the tube. If sufficient electrons are available an arc is struck and the starter plays no further part until the next starting operation. If there are insufficient electrons, the tube will flicker, fail to start, and the starter will repeat the heating of the cathodes. The ballast limits the current to a safe and appropriate level for the power of lamp. Without the ballast, the current would increase to a high level and the lamp would destroy itself.



Figure 5.8. Fluorescent lamp circuit.