Incandescent light

“ If, instead of the light of the sun, we examine prismatically the light given off by an incandescent body, such as a white-hot piece of platinum, we shall find that the lines seen in the solar spectrum are absent, and that we have a continuous band of coloured light quite uninterrupted by dark spaces or bands. The same absence of lines is seen in the spectra of the electric light and the flame of an ordinary candle, the light in each of these cases being produced by particles of carbon in a state of vivid incandescence. ”

“ 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. ”

“ The electric light is coincident with electric heat; the art of producing a brilliant light is the art of producing a high temperature. No greater illusion is extant than the idea that the electric light is a cold light, for the electric arc is the greatest source of heat known. This heat can be produced either by causing the electricity to fly across an air-space, in which case we have light by the arc, or an arc light, or by causing it to flow through a small wire or a carbon filament, which offers obstruction to the flow and produces light by incandescence, or the incandescent light. ”

“ But since they have seen an electric battery and an arc light, they should be ashamed to ever declare "the sun is hotter than any terrestrial furnace," or that it is hot at all. The arc and incandescent lights are object lessons they ought to study, for they will see almost an exact representation of how all light, heat and vital force are created on suns and planets. ”

“ When the sun failed to shine, or was not convenient, I practiced looking at a large incandescent electric light, and very soon the artificial lights troubled me no more than the stars which twinkle in the heavens at night ”

“ Visible radiation × visual sensibility is spoken of as luminosity; (3) by the amount of light (expressed in candles) produced in relation to a given expenditure of energy or in relation to the cost of the energy expended. Thus, of the radiation emitted from an incandescent electric lamp only a small per cent. is light, the rest being heat and actinic rays. It is therefore very far from being 100 per cent. efficient. If there were no infra-red or ultra-violet in the radiation from an incandescent lamp its efficiency would be 100 per cent. if we disregarded visual sensibility. ”

“ Artificial light is furnished by electricity, by gas, by oil in lamps, and in numerous other ways. Until modern times candles were the main source of light, and indeed to-day the intensity, or power, of any light is measured in candle power units, just as length is measured in yards; for example, an average gas jet gives a 10 candle power light, or is ten times as bright as a candle; an ordinary incandescent electric light gives a 16 candle power light, or furnishes sixteen times as much light as a candle. ”

“ 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. ”

“ 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. ”

“ Thus, while the incandescent electric bulb is a great advance over fire, it is still a very inefficient source of light. Because it depends upon incandescence, a considerable portion of the electrical input goes into the production of unwanted heat, for the bulb’s filament radiates in the infrared as well as the visible region. ”

“ At the present moment in ordinary incandescent or glow-lamp electric lighting we require to expend an amount of power, called one horse-power, to produce illumination equal to that of 600 candles. Supposing, however, that all our power could be utilized in generating merely the rays useful for vision, or which can impress our eyes, we might be able to create by the expenditure of one horse-power more than twenty times as much illumination, that is, a light equal to 12,000 candles. ”

“ He not only produced combustion, fusion, and incandescence by invisible radiation, but he proved that in the case of the electric light the invisible rays are no less than eight times as powerful as the visible radiations. He obtained all the colours of the solar spectrum from a platinum foil raised to incandescence at the invisible focus; and this rendering of a refractory body incandescent by invisible rays he called calorescence. ”

“ An ordinary carbon incandescent lamp yields about six per cent, of light to ninety-four per cent, of heat, the arc lamp about ten per cent, of light, while the mercury arc has climbed to the enormous efficiency of almost half light to half heat. ”

“ 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. ”

“ Early in his experiments he abandoned the voltaic arc, deciding that a successful lamp must be one in which incandescence is produced by a strong current in a conductor, the heat caused by the resistance to the current producing the glow and light. But when search was made for a suitable substance possessing the necessary properties to be the incandescent material, the inventor was confronted by a vast array of difficulties. ”

“ To thus examine the constituents of a beam of light a lantern, with a lime-light or electric light, may be used for throwing a constant beam; we may then produce an image of the cylinders of lime or the carbon points in the lantern on a piece of paper or a screen, and our eyes will tell us that this is an instance of how the radiations from any incandescent substance are competent to give us light. We receive all the rays to which our eyes are tuned and we see a white image on the screen. ”

“ White light, as we have seen, consists of a mixture of variously-coloured rays in very different and apparently arbitrary proportions, and if these proportions were a little changed the light would no longer be quite colourless. No ordinary artificial light is so exactly white as that of the sun. The light of candles, gas, oil, and electric glow-lamps is yellow; that of the electric arc (when unaffected by atmospheric absorption) is blue, and that of the incandescent gas burner green. ”

“ The light emitted is, at a distance, hardly distinguishable from that of a twenty-candle incandescent lamp, while a yellower light may be obtained by modifying the composition of the impregnating liquid. ”

“ 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. ”

“ Inventors also turned their attention to substances other than carbon which can be rendered incandescent by the electric current.
The luminous efficiency of any source of light, that is to say, the percentage of rays emitted which affect the eye as light compared with the total radiation, is dependent upon its temperature. In an ordinary oil lamp the luminous rays do not form much more than 3% of the total Oxide filaments. radiation. In the carbon-filament incandescent lamp, when worked at about 3 watts per candle, the luminous efficiency is about 5% ”

“ It is now a fact that a body may be rendered incandescent or phosphorescent by bringing it either in single contact or merely in the vicinity of a source of electric impulses of the proper character, and that in this manner a quantity of light sufficient to afford a practical illuminant may be produced. ”

“ An extreme case is that of the unpolarized light emitted by incandescent solid bodies, consisting of disturbances whose variations are highly irregular, and giving a continuous spectrum. But even with what is commonly called homogeneous light, no perfectly sharp line will be seen. ”

“ Holy Scripture become resplendent; or, as one might say, incandescent throughout.
I. Taylor.
Incandescent lamp or light (Elec.) , a kind of lamp in which the light is produced by a thin filament of conducting material, usually carbon, contained in a vacuum, and heated to incandescence by an electric current, as in the Edison lamp; -- called also incandescence lamp, and glowlamp.
In`ca*nes"cent (?) , a. [L. incanescens, p. pr. incanescere to become gray.] Becoming hoary or gray; canescent. ”

“ In diffused lighting, the lamp is covered, as by frosting, so that the rays of light are broken up and so scattered that no direct ray shines into the eyes, and there is no bright spot of light in the room. ”

“ Evidently there is some position in which the shadows are equally luminous. When that point is reached, I can read off the current which is passing through the lamp, and having previously standardized it for each increment of current, I know what amount of light is given out. This value of the incandescence lamp I can use as an ordinate to a curve, the scale number which marks the position of the color in the spectrum being the abscissa. ”

“ Yet in place of the sturdy bonfire of oak, or the huge iron cage full of coals, there is only a single lamp, whose rays are gathered by deep reflectors into a compact bundle of unwasted rays, and doubled and redoubled by rows of magnifying lenses until they can dart to the furthest horizon in a strong beam of steady light. ”

“ I must mention here that the Sun is not burning like a fire or a gas jet: it is glowing like an electric glowlamp. You know the difference between the two cases: a gas jet or candle gets quickly used up; but the filament of an electric light bulb, thin though it is, lasts for hundreds of hours without being consumed. The light comes, not from the consumption of the filament, but from the energy supplied to it from the electric power-house. The question we are considering is—what is the Sun's power-house, what is the source of the energy supplied which makes it glow? ”

“ Moreover, the further consequence ensues, that the sun is hotter than had been supposed; for, the higher the temperature of a glowing body, the more copiously it emits rays from the violet end of the spectrum. The blueness of its light is, in fact, a measure of the intensity of its incandescence. ”

“ 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. ”

“ As to the brilliancy of the flame, an appeal may be made to every one who has witnessed the gas-light illumination, whether it be not superior to the best wax candle-light, or the light of Argand’s lamps. ”

“ That is, we make eclipses of opaque shades revolving round the usual lighting apparatus, and these we can vary so as to show 5, 10, 15, 20 or 30 seconds of darkness with similar or greater intervals of bright light. We may thus use altogether white or bright lights, which have the greatest power to work in such a manner that one can be easily distinguished from another. ”

“ But even with ten lamps and reflectors, we do not get sufficient light; and we want, therefore, a means of getting a light more intense than a candle in the space of a candle—not merely184 an accumulation of candle upon candle, but a concentration, into the space of a candle, of a greater amount of light; and it is here that the electric light comes to be of so much value. ”

“ There should be no glaring lights, but a soft radiance which is so general as to make everything clear. An electric light hanging eighteen inches above the table, or a tall lamp whose light is at about the same height, either of them well shaded, are satisfactory additions to the candlelight. ”

“ The dissemination and diffusion of their light can be greatly aided by suitable colouring of ceilings, walls and drapings; but unless the illumination by means of lights of relatively high intensity is made almost wholly indirect, candles or other lights of low intensity, such as small electric glow-lamps, can, by proper distribution, be made to give more uniform or more suitably apportioned illumination. ”