Fluorescent lamp explosion and ballast

Shihab Uddin Ahmed | December 21, 2012

Fluorescent Tube photoUsage of fluorescent lamp is increasing because it’s four to six times efficient than incandescent lamp. Plasma state of matter is used in fluorescent lamps. Resistance of plasma decreases when electricity conducts through it. The danger lies in this property. Uncontrolled current through the plasma in the tube may produce heat and eventually the tube may explode.

Why the ballast?

Ballast or chock coli are used to control the current flow.

How the fluorescent lamp works and where is the danger?

Let’s talk about the working principle of the lamp. The tube contains some liquid mercury and inert gases like argon. When the lamp is switched on, the prevalent free electrons are energized and flow of electron starts. Applied electric field energizes the electrons. Then the electrons collide with other atoms more electrons are liberated, at the same time positive ions are also created.

These ions and electrons contribute in current flow. Resistance of the tube decreases and more currents flows according to Ohm’s law. The more currents flow through the tube, more ions and electrons are created and more current flows. Eventually excessive heat may explode the tube unless there is a circuit breaker.

How ballast curbs risk?

So, there needs something to control the current flow. Ballast or chock coil serves the purpose.

Chock coils are wire wound on magnetic substance which makes an inductor coil. The fluorescent lamp is connected to ac source which changes direction 100 or 120 times in a second. So the inductor coils acts like a resistance.

The coil stores magnetic energy when current flow in one direction increases and releases energy when current flow decreases. Even if resistance of the plasma becomes zero the chock coil blocks the increment.

This is why a coil is used instead of normal resistance.

Ballast photo

Any fluorescent lamps need ballast

Any fluorescent lamp, it may be street lamp (sodium or mercury) or compact fluorescent lamp require ballast.  Some electronic ballasts are available in market where current is controlled by electronic circuits.


Low intensity hum from ballast is normal, if you hear deep hum from it, check the ballast or replace it with a new one for safety. Deep hum may be a sign of malfunction.

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