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Let There Be Light!

Here is a brief description of the operation and care of the two types of lamps used today—incandescent and fluorescent
 
The electric lights commonly used in homes and offices are of two general types: incandescent and fluorescent. The incandescent lamp, invented by Thomas A. Edison in 1879, is a very simple thing. It consists of a wire sealed in a glass lamp, from which the air has been removed or replaced by a mixture of certain inert gases. The wire offers resistance to the flow of electricity. The friction of the electrons in pushing their way through raises the temperature of the wire to the point where it glows or "incandesces." The higher the temperature, the whiter the light.

Tungsten is the metal now universally used for incandescent lamp filaments. It burns at about 5000 degrees Fahrenheit, a fantastic temperature higher than that of any other artificial heat ordinarily encountered by man. At this temperature, asbestos or fire brick would melt like candle wax under a match. Why doesn't the tungsten wire consume itself? Because there is no air . .. that is, oxygen ... in the bulb to support combustion, or burning.
 
In lamps smaller than about the 50-watt size, the air in the glass envelope or bulb is merely pumped out, leaving a vacuum or "nothing" inside. In most larger lamps, a mixture of nitrogen and argon is pumped in following the evacuation of the air. The purpose of these gases is to introduce some slight pressure on the filament and to retard evaporation of the tungsten. The filament not only lasts longer than it would in a plain vacuum, but during its useful life it can be burned at a higher temperature. This means better, brighter light.

In manufacture, the gas mixture is introduced at slightly under normal atmospheric pressure. The internal pressure tends to rise when the lamp is on, and in the case of lamps burning very brightly it goes a little above atmospheric pressure. This explains why the very brilliant lamps used in movie and still projectors, and in spotlights, often develop blisters and bulges. The intense heat of the filament softens the glass, and the rising gas pressure inside forces it outward. A projection bulb that has been used a long time takes on a really grotesque appearance.

Will it pop out? Probably not for quite a while. Bulge in side of 300-watt projector lamp is due to combination of high filament temperature and inside gas pressure. Blackening  is  also natural.
 
In most straight fluorescent fixtures, the starter is accessible only after the lamp is removed. It is not screwed in. but is held by contact springs. A quarter turn will serve to loosen or lighten it.

Eventually, the filament of an incandescent lamp consumes itself. The metal evaporates to the point of such thinness that it simply burns open. Any lamp burns up almost instantly if the glass envelope is broken. The super-heated tungsten combines with the oxygen of the air and goes pfft!

If heat rather than light is wanted from an incandescent lamp, it is operated at a lower than normal temperature. In this class is the "infrared" lamp, which is widely used for the treatment of muscular pains and aches.

If a great deal of light is wanted, a tungsten lamp is operated at higher than normal temperature. Of course, its life is thereby shortened, and this is the price paid for the increased brilliance. The popular "Photoflood" lamps used in picture-making are actually 64-volt bulbs operated on 115 volts. Their rated life is about six hours, compared with about 750 hours for a regular 115-volt bulb.

When a lamp fails to light, and another lamp tried in the same socket does light, it obviously has expired. Every home should have a supply of spares. It's possible to double-check a lamp by running a continuity test on it, but this is rather pointless. It takes less time to screw in a new lamp.

There are only a few simple precautions to observe in using incandescent lamps, and these relate mainly to their high operating temperature. Don't let paper, parchment, silk or other cloth shades come in direct contact with the glass. The material can readily char, and under some circumstances will actually burst into flames. Don't touch a hot bulb with your bare hands. If you don't want to wait until it cools off, grasp it with a handkerchief or a pot holder. Avoid splashing water on a bare bulb; the glass might implode (get that, implode) and scatter fragments all over the room.

DO keep lamps clean and dust-free by wiping them occasionally, when cool, with a very slightly dampened cloth. Bulbs inside decorative globes or fixtures are often neglected in this respect and gradually become dim. Internal blackening is another matter, and cannot be avoided. It is the natural result of gradual evaporation of the tungsten filament. Sometimes the blackening reduces the light output to the point where it is more economical to replace the bulb, even though it still lights, than to continue to use it.

Westinghouse Electric Corporation

According  to   scientists,  electrons  inside   fluorescent  lamp  release  ultraviolet  radiation  from  mercury.

The color of the light produced by flourescents depends on the chemicals or "phosphors" used as the coating. While -white is the most usual color (actually, white is not a color, but a combination of all colors), it is also just as easy to obtain blue, orange, green, blue-white, yellow-pink, deep red and ultra-blue.

The electron-emitting electrode in each end of the tube is called a "cathode." In the

Ii you suspect that the cathode wire is burned out, a continuity check with Handitester will give the answer. However, filament wires rarely burn out.

Fluorescents Are Different

In a filament lamp, electric current flows through a solid tungsten wire and heats it to incandescence. In a fluorescent lamp, the two electrodes which are connected to the power line are completely separated inside a long glass tube. The latter contains a small drop of mercury, and its inner surface is coated with a chemical that has the property of glowing or "fluorescing" when struck by ultraviolet light, which itself is not visible to the human eye. Under the proper conditions, electrons flow back and forth between the end electrodes under the impetus of the line voltage. The theory is that they strike atoms of the mercury and release the ultraviolet radiation, which in turn impinges on the chemical coating and causes it to fluoresce.

When removing or inserting lamp, make sure pins at both ends drop straight into slots in sockets; then   twist  quarter   turn.   Don't  force   into  place.

Annoying humming sound heard from fluorescent lamps is from vibration of core of ballasts. Remount the  ballasts  on  large fiber  or  leather  washers.

After installing fiber washers, tighten screws of ballasts only enough to assure grip. Ii you compress them too much, they won't silence ballasts.

Ii new starter and new lamp don't .produce light. check the ballast with your Handitester for continuity. The  normal reading is around 30 ohms.

Receptacle for starter and socket for end of lamp are often combined. H they break from being forced,   it's   a   simple   matter   to   replace   them.

Pencil points to one of two ballasts concealed inside body of fluorescent fixture. When the latter   is    opened,   it   is   easy   to   trace    •wiring.

Standard two-lamp fluorescent fixture is usually snap-assembled. To take apart, separate body from base with thin screwdriver, squeeze body slightly.

General Electric Company

These are common types of hot cathodes used in fluorescents. In preheat cathode, current flows first through filament, just as in incandescent lamp, and then is cut off. In instant-start cathode, the electrons are pulled off the surface by high operating voltage. While the instant-start type has a filament, its ends are short circuited in the stem and only one  external connection is needed for it fluorescents in most common use, this is a coiled tungsten wire filament, coated with a chemical that gives off electrons freely when heated. The tungsten filament does not contribute any illumination directly. Two auxiliary devices are needed to make the lamp work: a "starter" and a "ballast." In a basic lamp, the filaments, the ballast and the starter are connected in simple series. When the lamp switch is turned on, current flows through all the elements. The filaments can be seen to glow slowly. After a second or two, the contacts inside the starter snap open. This cuts off the current to the filaments, and at the same time causes the ballast to develop a momentarily high-voltage "kick." Surging through the lamp, this voltage starts acting on the electrons already loosened from the hot cathodes, and the double cycle previously described gets under way. One side of the AC power line remains connected to one terminal only of one cathode; the other side of the power line goes to the ballast, which in turn connects to one terminal only of the second cathode. The filaments themselves are no longer incandescent. The electrons are pulled off their surfaces by the mere attraction of the voltage between the cathodes.

 
Westinghouse Electric Corporation

Above is a diagram of a typical two-lamp instant-start fluorescent. The ballast in this type of lamp contains a step-up transformer for boosting line voltage plus a capacitor for improving power factor.
 
The ballast is a coil of fine wire on an iron core. It looks exactly like the "choke" coils found in radio and television sets. Once the arc inside the lamp is struck, the ballast acts to limit the current flow between the cathodes within prescribed values for each particular size and type of lamp. Ballasts generally have long life, but they carry current and are therefore susceptible to eventual failure.

Some lamps have "instant" cathodes which do not require pre-heating. They do require much higher starting voltages to jar the electrons loose. No starter is needed, as the first pulse of voltage is enough to start the electrons on their way.

In the glow-switch starter pictured above, glass bulb is tilled with neon or argon, depending on lamp voltage. On starting, voltage at starter is sufficient to produce a glow discharge between U-shaped bimetallic strip and fixed contact or center electrode (a). Heat from glow actuates bimetallic strip, contacts close and cathode preheating begins (b). This shorts out glow discharge, bimetal  cools  and  shortly  the  contacts  open  (c).

 

At right is a diagram of a thermal-switch starter. On starting, the ballast, starter heating element and lamp cathodes are all in a series across the line since contacts of thermal-switch starters are normally closed. Cathode preheating current thus also heats the bimetallic strip in the starter and the contacts open. The inductive kick then starts the lamp itself with the normal operating current thereafter   holding   thermal   switch   (inset)   open.

General Electric Watch Dog Manual Reset Starters use glow switch principle. During normal starting switch functions as described under illustration at left. This starter has an added feature which consists of a wire-coil heater element actuating a bimetallic arm which serves as a latch to hold a second switch in a normal closed position. When a lamp is deactivated or will not start after blinking on and off, enough heat is developed by intermittent flow of cathode preheating current so that latch pulls away and releases second switch.

Unlike incandescent lamps, which will light under almost any conditions of line voltage, temperature and humidity, fluor-escents are known to be somewhat sensitive in these respects. Their susceptibility to cold, especially, is not too generally appreciated, and is the reason for many mysterious cases of irregular or unsatisfactory operation. In an unheated garage or a partially heated basement, lamps sometimes don't strike at all in winter weather, but keep blinking on and off.

If a flourescent fixture has been working properly over a period of time, and then either refuses to start or works fitfully, either the starter or the lamp itself might be at the end of its useful life. Always try a new starter first, as it's much cheaper than a new lamp. If the trouble continues, you have no choice but to try a new lamp.
If the ends of a lamp remain lighted steadily, with no sign of the tube striking for its full length, the strong likelihood is that the starter contacts have welded shut, or possibly a short circuit has developed in the little capacitor which is included in some starters to eliminate radio interference.

The filament wires of cathodes rarely burn out because they are heated to full incandescence for only a few seconds during the starting period. However, it is easy to test them with any continuity checker.

A new lamp may show swirling, spiral-ing, snaking or fluttering effects when first turned on, but usually clears up after it is well warmed up or has been turned on and off a few times. An old lamp sometimes starts swirling violently, and then resumes clear operation without warning. This is probably due to shifting distribution of the phosphors on the inside of the glass. ·

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