FLUORESCENT TUBE

Hello Folks,

Even though fluorescent lights all around us, this devices is a total mystery to most people. We will just have a look what is going on inside these white tubes? We will analyze how fluorescent lamps emit such a bright glow without getting scalding hot like an ordinary light.

The general design of a simple fluorescent lamp consists of a sealed glass tube. The tube contains a small bit of mercury and a gas (usually argon) kept under very low pressure. The tube also contains a phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each end, which are wired to an electrical circuit. The electrical circuit, which includes a starter and ballast, is hooked up to an alternating current (AC) supply.

When you turn on the tube light, current flows through the electrical circuit to the electrodes. When an AC voltage is applied to a tube light fixture, the voltage passes through the choke, the starter, and the filaments of the tube. There is a considerable voltage across the electrodes (approximately 1000V), so electrons will migrate through the gas from one end of the tube to the other. This energy changes some of the mercury in the tube from a liquid to a gas. As electrons and charged atoms move through the tube, some of them will collide with the gaseous mercury atoms. These collisions excite the atoms, bumping electrons up to higher energy levels. When the electrons return to their original energy level, they release light photons. As electrons return to their original energy level, they begin to release light. However, the light they emit is ultraviolet, and not visible to the naked eye. This is why the tube was coated with phosphorous. When exposed to the ultraviolet light, the particles emit a white light which we can see. Once the conduction of electrons between the electrodes is complete, no more heating of the filaments is required and whole system works at a much lower current. The entire fluorescent lamp system depends on an electrical current flowing through the gas in the glass tube. The figure explains how an atom emits electron and how exactly is the current flow and working of fluorescent tube.

The starter is basically a time delay switch. Its job is to let the current flow through to the electrodes at each end of the tube, causing the filaments to heat up and create a cloud of electrons inside the tube. The starter then opens after a second or two. The voltage across the tube allows a stream of electrons to flow across the tube and ionize the mercury vapor. Without the starter, a steady stream of electrons is never created between the two filaments, and the lamp flickers.

The ballast works mainly as a regulator. They consume, transform, and control electrical power for various types of electric-discharge lamps, providing the necessary circuit conditions for starting and operating them.

In a fluorescent lamp, the voltage must be regulated because the current in the gas discharge causes resistance to decrease in the tube. The AC voltage will cause the current to climb on its own. If this current isn’t controlled, it can cause the blow out of various components.

Today the most popular fluorescent lamp design is “rapid start” lamp (without Starter).

Concluding the discussion, we can say that the basic principle is: an electric current stimulates mercury atoms, which causes them to release ultraviolet photons. These Photons in turn stimulate a phosphor, which emits visible light photons.

Thank you for your time. Do comment about your area of interest.