Tube-light starter

SRI HARSHA

Visakhapatnam, Andhra Pradesh

The role of a starter in a tube-light is to initiate or start striking of electrical discharge along the column or length of the tube. Basically a conventional tube-light called as fluorescent-lamp is a low pressure mercury vapour lamp, a type of electrical discharge lamp.

When electrical discharge strikes through the column of the tube, a lot of invisible ultra-violet radiation is generated. This invisible ultra-violet light is converted to useful visible light by the process, fluorescence, with the help of fluorescent material called phosphors seen as a white coating in the inner wall of the tube.

In order to first initiate the discharge process a high surge current should be sent through the circuit which is achieved with the ballast — choke-starter combination. An ordinary fluorescent lamp uses a glow-switch type starter made of a tiny bulb enclosing a set of two small closely spaced electrodes, of which at least one is made of a bi-metallic strip.

The bulb is filled with a mixture of rare-gases usually Argon-Neon mixture.

As the mains voltage supply is closed, first discharge occurs between the electrodes of the starter. This discharge makes the bimetallic strip hot and hence deflects the bi-metallic strip towards the other electrode and there by short-circuiting and hence breaking of the circuit.

So again discharge strikes between the electrodes of starter, again breaking and so on. This repeated momentary closure, breaking of the circuit through the starter generates lot of surge current to establish self-sustainable discharge along the column of the lamp-tube. Once the discharge is built-up in the lamp tube the starter becomes redundant.

In the initial stage of lamp switching on, the discharge across the electrodes of the starter is seen as flickering, a pale red glow seen through the translucent enclosure of the bulb.

Of late with the advent of improved electronics lots of improvements in the lamp-design have become possible like flicker-free compact fluorescent lamps.

R. JAGANNATHAN

Luminescence Group, CECRI

Karaikudi, Tamil Nadu

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