Light Bulb Manufacture
Cathode ray tubes, light bulb manufacture
How Light bulbs work and how they are
Manufactured.
From the earliest periods of history until the beginning of the
19th century, fire was man's primary source of light. This light
was produced through different means-torches, candles, oil and gas
lamps. Besides the danger presented by an open flame (especially
when used indoors), these sources of light also provided
insufficient illumination.
The first attempts at using electric light were made by English
chemist Sir Humphry Davy. In 1802, Davy showed that electric
currents could heat thin strips of metal to white heat, thus
producing light. This was the beginning of incandescent (defined as
glowing with intense heat) electric light. The next major
development was the arc light. This was basically two electrodes,
usually made of carbon, separated from each other by a short air
space. Electric current applied to one of the electrodes flowed to
and through the other electrode resulting in an arc of light across
the air space. Arc lamps (or light bulbs) were used mainly in
outdoor lighting; the race was still on among a large group of
scientists to discover a useful source of indoor illumination.
The primary difficulty holding back the development of a
commercially viable incandescent light was finding suitable glowing
elements. Davy found that platinum was the only metal that could
produce white heat for any length of time. Carbon was also used,
but it oxidized quickly in air. The answer was to develop a vacuum
that would keep air away from the elements, thus preserving the
light-producing materials.
Thomas A. Edison, a young inventor working in Menlo Park, New
Jersey, began working on his own form of electric light in the
1870s. In 1877 Edison became involved with the rush for a
satisfactory electric light source, devoting his initial
involvement to confirming the reasons for his competitors'
failures. He did, however, determine that platinum made a much
better burner than carbon. Working with platinum, Edison obtained
his first patent in April of 1879 on a relatively impractical lamp,
but he continued searching for an element that could be heated
efficiently and economically.
Edison also tinkered with the other components of the lighting
system, including building his own power source and devising a
breakthrough wiring system that could handle a number of lamps
burning at the same time. His most important discovery, however,
was the invention of a suitable filament. This was a very thin,
threadlike wire that offered high resistance to the passage of
electric currents. Most of the early filaments burned out very
quickly, thus rendering these lamps commercially useless. To solve
this problem, Edison began again to try carbon as a means of
illumination.
He finally selected carbonized cotton thread as his filament
material. The filament was clamped to platinum wires that would
carry current to and from the filament. This assembly was then
placed in a glass bulb that was fused at the neck
(called sealing-in). A vacuum pump removed the air
from the bulb, a slow but crucial step. Lead-in wires that would be
connected to the electrical current protruded from the glass
bulb.
On October 19, 1879, Edison ran his first test of this new lamp.
It ran for two days and 40 hours (October 21-the day the filament
finally burned out-is the usual date given for the invention of the
first commercially practical lamp). Of course, this original lamp
underwent a number of revisions. Manufacturing plants were set up
to mass produce light bulbs and great advances were made in wiring
and electrical current systems. However, today's incandescent light
bulbs greatly resemble Edison's original lamps. The major
differences are the use of tungsten filaments, various gases for
higher efficiency and increased lumination resulting from filaments
heated to higher temperatures.
Although the incandescent lamp was the first and certainly the
least expensive type of light bulb, there are a host of other light
bulbs that serve myriad uses:
- Tungsten halogen lamps
- Fluorescent lamps are glass tubes that contain mercury vapor
and argon gas. When electricity flows through the tube, it causes
the vaporized mercury to give off ultraviolet energy. This energy
then strikes phosphors that coat the inside of the lamp, giving off
visible light.
- Mercury vapor lamps have two bulbs-the arc tube (made of
quartz) is inside a protecting glass bulb. The arc tube contains
mercury vapor at a higher pressure than that of the fluorescent
lamp, thus allowing the vapor lamp to produce light without using
the phosphor coating.
- Neon lamps are glass tubes, filled with neon gas, that glow
when an electric discharge takes place in them. The color of the
light is determined by the gas mixture; pure neon gas gives off red
light.
- Metal halide lamps, used primarily outdoors for stadiums and
roadways, contain chemical compounds of metal and halogen. This
type of lamp works in much the same fashion as the mercury vapor
lamps except that metal halide can produce a more natural color
balance when used without phosphors.
- High-pressure sodium lamps are also similar to mercury vapor
lamps; however, the arc tube is made of aluminum oxide instead of
quartz, and it contains a solid mixture of sodium and mercury.
Gas back filling of Neon Tubes
The invention relates to a system and method for automatically
evacuating neon tubes and filling the tubing with a neon gas or gas
mixture.Previously, various pumping systems have been proposed for
evacuating and filling neon tubes, such as used in neon signs, with
neon and other gas mixtures. Typically, the neon pumping system has
included a manifold, a mechanical pressure gaugehaving a visual
display connected to the manifold, and a series of greaseless
stopcock valves, which are manually operated, controlling the
various flows in the manifold. The stopcock valves typically
connect the neon tubes with a vacuum pump assembly,and a source of
replenishment gas, such as neon or other gas mixture. Stations for
filling neon tubes may be placed on opposing ends of the manifold.
There is a system stopcock connected between the manifold and the
vacuum pump. A diffusion pump maybe connected in a by-pass line
with the vacuum pump so as not to be connected in use except after
the vacuum has been reduced to a certain level, and it is necessary
to achieve an even higher vacuum. Alternatively, a diffusion pump
may be connected in asecond line, with a second vacuum pump. In
use, the system stopcock is opened, and the main stopcock to the
vacuum pump is opened simultaneously with turning on the pump. The
system is manually operated to control the pressure in the tubes as
visuallydetermined from the gauge display, and evacuate the tubes
to a desired vacuum whereupon the system stopcock to the vacuum
pump is closed. During the evacuation process, an electrical
potential is placed across the neon tubes to cause the tubes and
gasestherein to be heated. The stopcock to the vacuum pump may be
opened if the pressure becomes too high in the tube during heating.
When the temperature and vacuum conditions inside the tube have
reached a desired level the electrical potential is removedfrom the
tubes, and the tubes are allowed to cool. Afterwards, the stopcock
to the gas source is
Cathode Ray Tube
The Cathode Ray Tube
Almost all TVs in use today rely on a device known as
the cathode ray tube,
or CRT, to display their
images. lcd and plasma displays
are sometimes seen, but they are still rare when compared to CRTs.
It is even possible to make a television screen out of thousands of
ordinary 60-watt ligh bulbsYou may have seen
something like this at an outdoor event like a football game. Let's
start with the CRT, however, because CRTs are the most common way
of displaying images today.
The terms anode
and cathode are used in electronics as
synonyms for positive and negative terminals. For example, you
could refer to the positive terminal of a battery
as the anode and the negative terminal as the cathode.
In a cathode ray tube, the "cathode" is a heated filament (not
unlike the filament in a normal light bulb). The
heated filament is in a vacuum created inside a glass "tube." The
"ray" is a stream of electrons that naturally pour off a heated
cathode into the vacuum.
Electrons are negative. The anode is positive, so it attracts
the electrons pouring off the cathode. In a TV's cathode ray tube,
the stream of electrons is focused by a focusing anode into a tight
beam and then accelerated by an accelerating anode. This tight,
high-speed beam of electrons flies through the vacuum in the tube
and hits the flat screen at the other end of the tube. This screen
is coated with phosphor, which glows when struck by the beam.
