How Tub-light Works

Brief Description:

 A tube light works by using the principle of fluorescence. The fluorescent tube contains two filaments, one at each end of the tube, which glow to heat up the gas contained inside the tube. 

The inner surface of the tube is coated with compound of elements such as phosphorus having fluorescence. While manufacturing, the tube is filled with a small amount of a gas such as mercury vapor (for a white color), carbon dioxide (for green), neon (for red color), etc. 

                             

The power supply is delivered to the tube through starter and choke. When the supply is turned on, the two filaments glow and the contacts of the starter becomes open. This action provides a high voltage across the tube and this ionizes the warmed-up gas inside the tube. This ionized gas excites the fluorescent coating inside of the tube so that it gives out visible light.

Choke:

        The choke is a current limiter. A high initial voltage is required to fire the tube,   and then the current must be limited to keep the bulb from burning up.

Most ballasts nowadays are actually solid state electronic. They can run the tube at a higher frequency than the AC line making it more efficient, last longer, and correct the power factor making the load on the electrical system less. 

All circuit of neon tube light is like this: L(live), inductor, first heater, starter, second heater, N(neutral) connected in series. Starter is gas glow bulb where one of electrodes is made of bi-metal, and parallel capacitor for RFI. When you switch on starter bulb is short circuited and heating current flows through series circuit. After some time (few second) gas bulb is heated enough and bi-metal electrode break the series circuit. Sudden reduce in circuit current causes induction of high voltage on inductor and so on the opposite electrodes of neon tube. Neon tube starts to glow giving the light. At the same time the starter bulb continue to glow and keep hot preventing bi-metal electrode to close again. Start of neon tube may be clean or through few attempts (flickering). Inductor limits the neon tube voltage when it glows to abt. 50V.

Starter:

                   Fluorescent starters are used in several types of fluorescent lights. The starter is there to help the lamp light. When voltage is applied to the fluorescent lamp, here's what happens:

1. The starter (which is simply a timed switch) allows current to flow through the filaments at the ends of the tube.
2. The current causes the starter's contacts to heat up and open, thus interrupting the flow of current. The tube lights.
3. Since the lighted fluorescent tube has a low resistance, the ballast now serves as a current limiter.

When you turn on a fluorescent tube, the starter is a closed switch. The filaments at the ends of the tube are heated by electricity, and they create a cloud of electrons inside the tube. The fluorescent starter is atime-delay switch that opens after a second or two. When it opens, 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. Without the ballast, the arc is a short circuit between the filaments, and this short circuit contains a lot of current. The current either vaporizes the filaments or causes the bulb to explode.

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