Incandescent lamp

“ The most convenient practical working standard is an incandescent lamp run at a high temperature, that is, at an efficiency of about 21/2 watts per candle. If it has a sufficiently large bulb, and has been aged by being worked for some time previously, it will at a constant voltage preserve a constancy in illuminating power sufficiently long to make the necessary photometric comparisons, and it can itself be compared at intervals with another standard incandescent lamp, or with a flame standard such as a Harcourt pentane lamp. ”

“ The life of all incandescent lamps varies inversely with the voltage. An increase in voltage will produce an increase in the efficiency of the lamp but shorten its life. The efficiency decreases with continued use, and it is generally considered that the useful life of a lamp is over when its efficiency has fallen to 80 per cent of its original value. Frosting or coloring shortens the life of lamps from 30 to 50 per cent and reduces the candle power from 3 to 10 per cent, but the lamp yields a more pleasing light. ”

“ The incandescent lamp, or electric lighting by incandescence, underwent a somewhat longer evolution at the hands of inventors than the arc lamp, owing to the difficulty of finding a substance suitable for the production of the necessary glow. The discovery of such substance may be accredited to Edison more fully than to any other. The incandescent or glow lamp is a glass bulb from which the air is exhausted. ”

“ From an artistic point of view, one of the worst methods of lighting a room is by pendant lamps, collected in single centres in large numbers. The lights ought to be distributed in different portions of the room, and so shaded that the light is received only by reflection from surrounding objects. Ornamental effects are frequently produced by means of candle lamps in which a small incandescent lamp, imitating the flame of a candle, is placed upon a white porcelain tube as a holder, and these small units are distributed and arranged in electroliers and brackets. ”

“ During the past few years the manufacture of incandescent lamps has been developing rapidly, numerous improvements having been introduced, and by the use of high class of photometrical instruments in the examining rooms, the exact light-giving power of each lamp in standard candles is registered, the ordinary sizes being 5, 8, 12, 16, 25, 30, and 50, those of higher power being only suitable for halls, ball-rooms, &c. ”

“ It is securely fastened to the table, which in its turn is fastened to the floor, and the light is supplied by a small incandescent lamp within the chimney, but concealed by the shade. The visitor never imagines that it is an electric lamp, and naturally thinks that it would be impossible for a kerosene lamp to be inverted without disaster, so that this adds to the deception materially. ”

“ The fire that cooks our food gives off a quantity of useless light-waves; the oil-lamp that brightens one’s rooms gives off a quantity of useless, often obnoxious, heat.
The ideal illuminant and the ideal heating agent must be one in which the required waves are in a great majority. Unfortunately, even with our most [Pg 343] perfected methods, the production of light is accompanied by the exertion of a disproportionate amount of wasted energy. In the ordinary incandescent lamp, to take an instance, only 5 or 6 per cent. of the energy put into it as electricity results in light. ”

“ We may add that each of the standard incandescent lamps requires only about one-quarter of an ampère of current to make them give a light of 16 candle-power, which is about the light given by a very good gas-jet, and while the electromotive force, or pressure, would only be about 110 volts, whether there were one lamp or ten thousand lighted, there must be sufficient ampères in the wires to give each lamp its proper quantity. ”

“ A parabolic reflector sends forth as parallel rays the powerful beam of a lighthouse, a locomotive, or a searchlight. An incandescent lamp of ingenious design is silvered on its upper half so that none of its light is wasted. Because the arc lamp is the cheapest of all illuminants it is adopted for out-of-door lighting where its unpleasant glare is tempered by distance. In factory lighting its brightness is excessive and [76] harmful unless moderated. A capital plan is to employ an ordinary continuous current and place the positive carbon, with its brilliant centre, below the negative carbon ”

“ But such a lamp would possess a vast advantage over an ordinary incandescent lamp in regard to efficiency. It is well-known that the efficiency of a lamp is to some extent a function of the degree of incandescence, and that, could we but work a filament at many times higher degrees of incandescence, the efficiency would be much greater. In an ordinary lamp this is impracticable on account of the destruction of the filament, and it has been determined by experience how far it is advisable to push the incandescence. ”

“ An incandescent lamp, mounted on a powerful coil, is lit without contact by ether waves transmitted from a cable running round the laboratory, or bulbs and tubes containing highly rarefied gases are placed between two large plate-terminals arranged on the end walls. As soon as the bulbs are held in the path of the currents passing through the ether from plate to plate they become incandescent, shining with a light which, though weak, is sufficiently strong to take photographs by with a long exposure. ”

“ We are standing today on the threshold of an entirely new era in lighting. New illuminants are being developed and new methods are being devised for applying light to meet the needs of modern living. Only a little over a third of a century has passed since the first incandescent lamp was invented by Thomas A. Edison, and the electrical industry has since made tremendous progress. ”

“ While the copper and platinum wires readily conduct the current, the carbon filament offers a great deal of resistance to its passage, and for this reason becomes very hot, in fact is raised to white heat or incandescence, which gives its name to the lamp. ”

“ Incandescent means to glow with heat—In short the incandescent light is one which employs a globe in which the air has been exhausted and in which a vacuum exists. Before the air has been exhausted a filament of metal has been affixed through which the current of electricity is passed. In the resistance of this current the filament glows and gives the light that you use.
Don’t take any lamp you can get. Ask for the number of candle power or watts you want. The lamps to-day are more popularly sold according to watts rather than candle power. ”

“ The burning of an incandescent lamp at any candle power when connected across a heavy metal bar, the existence of nodes on the bar and the possibility of exploring the bar by means of an ordinary Cardew voltmeter, are all peculiar developments, but perhaps the most interesting observation is the phenomenon of impedance observed in the lamp with a straight filament, which remains dark while the bulb glows. ”

“ But it was a scarce and expensive material, and so long as it was heated to incandescence in the open air, that is, so long as its heat was fed as other heat is, by oxygen, it was slowly consumed. Platinum is no longer in the field of electric lighting, and the substitute which takes its place in the present incandescent lamp, and which is known as a "filament," is not heated in contact with the air. The experiments and endeavors that brought this result constitute the story of the incandescent lamp. ”

“ This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.
THE GAS-FILLED TUNGSTEN LAMP
The higher the temperature at which an incandescent lamp filament can be operated, the more efficient it becomes. The limit in temperature is reached when the material begins to evaporate rapidly, which blackens the bulb. The filament becoming thinner more quickly, thus rupturing sooner, shortens the life. If, therefore, the evaporating temperature can by some means be slightly raised, the efficiency will be greatly improved. ”

“ It was evolved from the early observed fact that a conductor is heated when traversed by an electric current, and that if it has a high resistance and a high melting-point it may be rendered incandescent, and therefore become a source of light. Naturally every inventor turned his attention to the employment of wires of refractory metals, such as platinum or alloys of platinum-iridium, &c., for the purpose of making an incandescent lamp. ”

“ On no account, however, should an arc light be used, as besides being too dazzling, it is much too uncertain; in fact many other reasons could be given for rejecting it. It is even a question whether it is an advantage to have incandescent lamps for a mast-head light. There is certainly the great advantage of not having to pull the lamp up and down to trim it, a rather risky performance in heavy weather, and also of the light not being affected by any wind that may get into the lamp ”

“ The lamps referred to here are those having a pear-shaped glass bulb, and which are known as incandescent lamps. The kind we see in the streets, giving a very powerful light, are called arc-lights. With this class of lights, however, we will have nothing to do here. The object of this article is to give plain directions for the construction of a battery to light a small electric lamp. Some boys may think that because electricity is something mysterious it must be very difficult to produce ”

“ It must be remembered that electric lighting is comparatively a new science, and not yet fully understood. There is very little doubt that, by practice, it will before long approach more nearly to perfection, and sooner or later entirely supersede gas, the arc form of lamp being employed for the illumination of streets and large areas, while the incandescent pattern meets domestic requirements.—Good Words. ”

“ None, it is stated, have broken, even when forced much beyond the incandescence they are intended to bear, and, owing to the compensating action of the gasoline, it is anticipated that the lamps will be permanent. The platinum wires supporting the carbon strip are not fused into the glass of the bulb, as has been the case in previous incandescent lamps, but are surrounded by a slightly elastic cement, which it is averred preserves a good joint. The light given by the lamp is but slightly yellow, is quite pleasing to the eye, and is fairly steady. ”

“ An ingenious device has lately been added to the system for facilitating the lighting of the lamp. At the base of the lamp-post a small hermetically-closed can containing petroleum ether is placed, and connected by very fine copper-tubing with a burner under the vaporising tube. When the lamp is to be lit a small rubber bulb is squeezed, forcing a quantity of the ether vapour into the burner, where it is ignited by a platinum wire rendered incandescent by a current passing from a small accumulator also placed in the lamp-post. ”

“ An improvement, therefore, in the efficiency of the incandescent lamp can only be obtained by finding some substance which will endure heating to a higher temperature than the carbon filament. Inventors turned their attention many years ago, with this aim, to the refractory oxides and similar substances. Paul Jablochkoff in 1877 described and made a lamp consisting of a piece of kaolin, which was brought to a state of incandescence first by passing over it an electric spark, and afterwards maintained in a state of incandescence by a current of lower electromotive force. ”

“ It is then immersed in plumbago and heated to a high temperature in order to destroy the organic matter. A carbon filament is the result. From this point to the finished lamp many operations are performed, but a discussion of these would lead far afield. The production of a high vacuum is one of the most important processes and manufacturers of incandescent lamps have mastered the art perhaps more thoroughly than any other manufacturers. ”

“ Even very unpretentious shows carry at least one spot lamp and the largest shows often carry 30 or 40 open and spot lamps. Arc lamps are often imitated by an incandescent lamp placed within a suitable globe with the hood made up in the shape of an arc lamp. ”

“ If the gas-filled tungsten lamp were used the amount of light now obtained for a cent would depend upon the size, which, for the 1000-watt lamp, would be 382 candle-hours.
STATISTICS REGARDING THE PRESENT DEMAND FOR LAMPS
In the United States there are about 350 million incandescent and about two hundred thousand magnetite arc lamps now (1923) in use. They are increasing about 10 per cent each year. The annual demand for incandescent lamps for renewals and new installations is over 200 millions, exclusive of miniature lamps. ”

“ Hence at points of high resistance in the filament, more heat being generated, a higher temperature is attained, and the scattering of the carbon becomes very rapid; in such cases the filament is sooner or later cut through at the point of high resistance. In order that incandescent lighting may be practically possible, it is essential that the lamps shall have a certain average life, that is, duration; and this useful duration is fixed not merely by the possibility of passing a current through the lamp at all, but by the rate at which the candle-power diminishes. ”

“ The various devices once placed are likely to last under ordinary usage as long as the householder will probably live to enjoy them; the only exception to this general statement being the lamp itself which, with the proper current for which it is constructed, is guaranteed to last one thousand hours. ”