Incandescent light bulb

“ 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 ”

“ A most ingenious yet simple device tells the workman when any particular crucible is in need of replenishing. A small, ordinary, incandescent electric-light bulb is placed in circuit between the poles that convey the electric current through the alumina solution. So long as the crucible contains alumina, the bulb does not glow, because twenty volts of electricity are required to make it incandescent, whereas seven volts pass through the solution. ”

“ If the incandescent light is four times as far away from the screen as the candle, and the shadows are equal, we know, by Section 100, that its strength is sixteen candle power. If the incandescent light is four times as far away from the screen as the candle is, its power must be sixteen times as great, and we know the company is furnishing the standard amount of light for a sixteen candle power electric bulb. ”

“ 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. ”

“ High candle-power lamps, 500, 1000 and upwards, are made by placing in one large glass bulb a number of carbon filaments arranged in parallel between two rings, which are connected with the main leading-in wires. When incandescent lamps are used for optical purposes it is necessary to compress the filament into a small space, so as to bring it into the focus of a lens or mirror. ”

“ 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 electric light in the form of the well-known powerful and dazzling arc-light is the favourite illuminant for lighting harbours, railway stations, docks, public works, and other large spaces. But it is to the incandescent lamp that one must look par excellence for the ‘light of the future.’ It has been satisfactorily established that lighting by incandescence is as cheap as lighting by gas, provided that it be carried out on an extensive scale. ”

“ It is never profitable, however, to use them for their whole lifetime. The lamp gradually volatilizes carbon and deposits [145] it upon the inner walls of the bulb, producing a smoky appearance and shutting off light. As the filament grows thinner by this process, it offers greater resistance to the current, and as the amount of current grows less the proportion of light to current grows rapidly less, so that at last instead of paying for 3.5 watts of electricity per candle-power of light one must pay for perhaps seven or eight watts per candle-power. ”

“ 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. ”

“ 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. ”

“ The little pear-shaped bulb with its delicate loop of filament, which cost months of toil and experiment at first, is now a common article, manufactured at an absurdly small cost, packed in barrelfuls and shipped everywhere, and consumed by the million. A means has been found for producing the vacuum of its interior rapidly, cheaply and thoroughly, and the beautiful incandescent glow hangs in lines and clusters over the civilized world. The phenomenon of incandescence without oxygen seems peculiar to these lights alone. ”

“ With the development of a waterproof base in 1900, by the use of a waterproof cement instead of plaster of Paris to fasten the base to the bulb, porcelain at first and later glass being used to insulate the terminals of the base from each other, lamps could be exposed to the weather and give good results. Electric sign lighting therefore received a great stimulus, and lamps as low as 2 candlepower for 110 volts were designed for this purpose. Carbon lamps with concentrated filaments were also made for stereoptican and other focussing purposes. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ The glow lamp having no carbon filament, but setting up a bright light with only a fraction of the resistance presented by carbon, would, if perfected, render electric lighting by far the cheapest as well as the best method of illumination. Tentative work has indicated a high degree of probability that success will be achieved, and the glowing bulb is at any rate a possibility of the future which it will be well to reckon with. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ The quality of light produced by an incandescent lamp is a gentler glow than that produced by the arc lamp, and in color more nearly resembles the light of gas or the oil lamp. The incandescent light speedily became for the home, hotel, hall, and limited covered area what the arc light became for the street and railway station, and, if anything, the former outstripped the latter in the extent and value of the industry it gave rise to. ”

“ 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 ”

“ 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. ”

“ 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. ”

“ Besides the voltaic arc, we have now, however, another kind of electric light—namely, the incandescence which is produced by sending the current through a very slender filament of platinum wire or carbon fibre inclosed in a glass bulb exhausted of air. Such are the lamps of Swan, Edison, and others. These lamps have also their curious features. The temperature of the filament is of course much lower than the temperature of the arc. ”

“ 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. ”

“ At lower pressures, when air becomes more or less conducting, or if the air be sufficiently warmed as to become conducting, the body is rendered more intensely incandescent in a large bulb, obviously because, under otherwise equal conditions of test, more energy may be given off from the body when the bulb is large.
At very high degrees of exhaustion, when the matter in the bulb becomes "radiant," a large bulb has still an advantage, but a comparatively slight one, over the small bulb. ”

“ The tube and bulbs are supported on their pivot so as to secure unstable equilibrium, so that, when the upper bulb begins to descend, it completes its excursion at once, and exposes the full bulb to the radiant heat, at the same time carrying its empty bulb behind the screen, where it cools. ”