Incandescent light principle

composition

This is an ordinary incandescent lamp, which is mainly composed of a glass bulb, a filament, a wire, a column, a lamp holder and the like.

Incandescent lamp

The glass bulb is made into a spherical shape, and the material is made of heat-resistant glass, which isolates the filament from the air, and can transmit light and protect. When the incandescent lamp is working, the temperature of the glass bulb can reach up to about 100 °C.

The filament is made of a tungsten wire that is much thinner than the hair, and is made spiral. It seems that the filament is very short. In fact, this very thin spiral tungsten wire is drawn into a straight line, which is more than 1 meter long.

The two wires of the wire are very simple on the surface, and actually consist of three parts: the inner wire, the Dumet wire and the outer wire. The inner wire is used to conduct and fix the filament, and is made of copper wire or nickel-plated wire; the short red wire in the middle is called Dumet, which is required to be intimately combined with the glass without leaking; the outer wire is copper wire, the task It is to connect the lamp head to energize.

A trumpet-shaped glass part of the column is the column of the sensor, which is attached to the glass case and acts as a fixed metal part. The exhaust pipe is used to pump the air out of the bulb, and then the lower end is welded and sealed, and the lamp does not leak.

The lamp cap is a metal piece that connects the lamp holder and is powered on, and is bonded to the glass bulb by solder.

It is especially necessary to talk about the filament here, because the electric light is illuminated by it.

Like carbon filaments, tungsten filaments in incandescent lamps are also afraid of air. If the glass bulb is filled with air, then after the power is applied, the temperature of the tungsten wire rises above 2000 °C, and the air will attack it without mercy, causing it to be blown quickly, and a yellow-white trioxide is generated. Tungsten, attached to the inner wall of the bulb and the inner part of the lamp.

If there is less air left in the glass bulb, then the process described above will proceed slowly. The oxidation of tungsten with air will produce a thin layer of blue mixture of tungsten trioxide and tungsten oxide.

Incandescent lamp

These are the tricks of air play - the oxygen in the air oxidizes the high temperature tungsten wire.

Therefore, the tungsten bulb should be evacuated and the air removed.

Sometimes I am afraid that the pump will not be cleaned, and I will also apply a little red phosphorus to the sensor column of the bulb. Red phosphorus will turn into white phosphorus when heated, and white phosphorus will easily react with oxygen to form solid phosphorus pentoxide, which will “eat” the oxygen, so that the residual oxygen in the glass bulb is also eliminated.

However, this has not solved all the problems. Incandescent lamps will turn black after a long time, and will burn out after a while. Do you know why?

Indeed, tungsten filaments evaporate much more slowly in a vacuum than carbon filaments. However, when the temperature of the incandescent lamp rises very high, the evaporation of tungsten is still very serious.

The high temperature for a long time causes the tungsten atoms on the surface of the tungsten wire to evaporate and diffuse like water vapor, and then deposits layer by layer on the inner surface of the glass bulb, so that the glass bulb is slowly blackened and more opaque.

The evaporation of tungsten also makes the tungsten wire thinner and finer, and finally blows. The higher the filament operating temperature, the faster the evaporation of tungsten and the shorter the life of the incandescent lamp.

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