Arc lamp

“ For indoor, public room or factory lighting, inverted arc lamps are sometimes employed. In this case the positive carbon is the lower one, and the lamp is carried in an inverted metallic reflector shield, so that the light is chiefly thrown up on the ceiling, whence it is diffused all round. The alternating-current arc is not only less efficient in mean spherical candle-power per watt of electric power absorbed, but its distribution of light is disadvantageous for street purposes. ”

“ In this lamp centring movements are usually dispensed with, the arc being clamped on to a tray pin as in the case of a limelight jet. This is not, of course, so convenient, and a further disadvantage of this pattern arc lamp is that the feeding process gradually alters the position and angle of the carbons. In fact, the one great merit of the lamp is cheapness, and where expense is an object, it should certainly be considered. ”

“ 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 ”

“ No light surpasses the arc light in brilliancy, excepting the magnesium light. There are few cities in this country and Europe that do not employ the arc lamp as a means of street, station, and large-area lighting, owing to its superiority as an illuminant and the wonderful policing effect it has upon the slum sections. ”

“ The introduction of enclosed arc lamps was a great improvement, in consequence of the economy effected in the consumption of carbon and in the cost of labour for trimming. A well-known and widely used form of enclosed arc lamp is the Jandus lamp, which in large current form can be made to burn for two hundred hours without recarboning, and in small or midget form to burn for forty hours, taking a current of two amperes at 100 volts. Such lamps in many cases conveniently replace large sizes of incandescent lamps, especially for shop lighting, as they give a whiter light. ”

“ 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. ”

“ Fire Dance.—This effect is generally illuminated from below the stage, the light being thrown upward through glass. Special arc lamps, equipped with powerful reflectors, are often used and generally several of them are required to produce the proper effect. If spot lamps are to be used they should not be turned upward but instead reflectors placed at an angle of forty-five degrees, should be provided to throw the light upward. See Figure 197. If a spot lamp is turned upward, the heat of the arc rising will be great enough to make condenser breakage a very serious problem. ”

“ It has been found by experience that the ordinary type of open arc lamp with vertical carbons included in an opalescent globe cannot compete in point of cost with modern improvements in gas lighting as a means of street illumination. The violet colour of the light and the sharp shadows, and particularly the non-illuminated area just beneath the lamp, are grave disadvantages. ”

“ The electric glow-lamp, and the most popular and economical modern enclosed electric arc-lamp, sterilise only the much smaller volume of air which is brought into direct contact with their glass bulbs. ”

“ The cost for labour and carbons is considerably reduced by the employment of the enclosed arc lamp, but owing to the absorption of light produced by the inner enclosing globe, and the necessity for generally employing a second outer globe, there is a lower resultant candle-power per watt expended in the arc. ”

“ Arc Lamps produce a light when a current passes from one carbon rod to the other across an air-space. As the current starts through the lamp, the ends of the carbons touch, and the imperfect contact causes resistance enough to heat the ends red-hot. ”

“ Whatever method of lighting we use therefore, enough resistance must always be kept in the circuit to ensure {41}that no more current can pass than has been provided for, and in the case of an arc lamp this usually means a resistance or rheostat being retained in the circuit in addition to the arc itself, through which the current is passed and absolutely wasted, though fortunately the waste in money is negligible, and for reasons to be discussed later such a resistance is necessary with an optical lantern arc lamp in any case. ”

“ The high-pressure flame arc lamp with inclined chemically treated carbons has, however, put a different complexion on matters. Although the treated carbons cost more than the plain carbons, yet there is a great increase of emitted light, and a 9-ampere flame arc lamp supplied with electric energy at 11/2d. per unit can be used for 1000 hours at an inclusive cost of about £s to £6, the mean emitted illumination being at the rate of 4 c.p. ”

“ 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. ”

“ Constant-potential lamps cannot be operated without resistance in the circuit; this resistance may be in the lamp itself or outside.
(6) Never handle high tension lamps without insulating yourself from the ground; and handle live wires only with one hand at a time.
(7) Provide spark arresters for all open-arc lamps in the vicinity of inflammable material.
(8) Never leave a lamp without globes where the wind can strike it. It will be blown out or feed often, thus consuming the electrodes very fast and at the same time yielding a very poor light. ”

“ Lighting as well as heating may share the gain of changing an old method for its contrary. Many forms of reflectors, both in glass and metal, have been designed to scatter the beams of lamps, usually in a downward direction. An excellent plan directs the positive carbon of an arc-lamp to the ceiling instead of to the floor; from the ceiling, duly whitened, the rays descend more thoroughly and agreeably diffused than if reflected from mirrors or refracted by prisms, however ingeniously shaped and disposed. ”

“ For the purpose of public illumination it is very usual to employ a lamp taking 10 amperes, and therefore absorbing about 500 watts. Such a lamp is called a 500-watt arc lamp, and it is found that a satisfactory illumination is given for most street purposes by placing 500-watt arc lamps at distances varying from 40 to 100 yds., and at a height of 20 to 25 ft. above the roadway. The maximum candle-power of a 500-watt arc enclosed in a roughened or ground-glass globe will not exceed 1500 candles, and that of a 6.8-ampere arc (continuous) about 900 candles. ”

“ 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. ”

“ Where the ceiling is very high or of an unsuitable colour, a sort of artificial ceiling in the shape of a large white reflector is placed above the lamp to produce the same effect. Sometimes the lamp is arranged so that part of the light is reflected to the ceiling, and part transmitted directly through a semi-transparent reflector below the lamp. The composition of the light of the arc lamp is very similar to that of sunlight, and by the use of such lamps the well-known difficulty of judging and matching colours by artificial light is greatly reduced. ”

“ When [140] it is desired to keep the arc at the focus of a reflector, both carbons must be fed.
Fig. 213 shows a theatre arc lamp, used to throw a strong beam of light from the balcony to the stage.
Fig. 214 shows the arc lamp used as a search-light. The reflector throws a powerful beam of light that can be seen for miles; in fact, the light is used for signalling at night. Fig. 215 shows how search-lights are used at night on war-vessels.
[141]
CHAPTER XXIII.
X-RAYS, AND HOW THE BONES OF THE HUMAN BODY ARE PHOTOGRAPHED.
Fig. ”

“ 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 ”

“ I am aware that arc lamps are used in the Royal Albert Docks, London, in connection with the dock lighting, lamps being carried below when required, with flexible leads attached, and that, in some few steamers, arc lamps have been used in the same manner in connection with their own plant. Arc lamps not suitable. These arc lamps are, I think, not nearly as suitable as incandescent lamps for the purpose of lighting up a ship’s hold; the light is too glaring, and casts deep shadows amongst the bales and cases, besides which, the lamps are large and clumsy. ”

“ 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. ”

“ In this case, an arc lamp or ordinary calcium light can be placed up in the loft, above the top of the cyclorama, and behind it. A little experimenting will reveal many striking light effects. If one light or lamp is not sufficient, others can be placed in various positions to reënforce [pg 89] it. As conditions vary so greatly, it is impossible to supply more concise directions. ”

“ If one lamp went out through the filament giving way, it would not affect the others, so that there would still be a light in the lantern. If, through some breakdown of the engine or dynamo, the electric current were no longer to be had, then it [42] Mast-head light. would only be necessary to withdraw the stand of lamps, and put in the ordinary regulation oil-lamp. The mast-head lamp could also be fitted with the electric light, as indeed has already been done. Arc light should never be used. ”

“ Edward Weston of Newark, New Jersey, also developed an arc lighting system. His commercial lamp had carbon rods, one above the other, and the arc was also differentially controlled. An oil dash pot prevented undue pumping of the carbons. His dynamo had a drum-wound armature, and had several horizontal field coils on each side of one pair of poles between which the armature revolved. The system was designed for about 20 amperes, each are taking about 35 volts. ”

“ Arc lamps, when used in places where they are exposed to flyings of easily inflammable material, must have the electrodes enclosed completely in a tight globe in such manner as to avoid the necessity for spark arresters. ”

“ Enclosed arc lamps are made to burn without attention for 200 hours, singly on 100 volt circuits, or two in series on 200 volt circuits, and in addition to the cost of carbons per hour being only about one-twentieth of that of the open arc, they have another advantage in the fact that there is a more uniform distribution of light on the road surface, because a greater proportion of light is thrown out horizontally. ”

“ Kennedy pointed to the incandescent lamp in the ceiling. "The incandescent lamp," he said, "is not always the mute electrical apparatus it is supposed to be. Under the right conditions it can be made to speak exactly as the famous 'speaking-arc,' as it was called by Professor Duddell, who investigated it. Both the arc-light and the metal-filament lamp can be made to act as telephone receivers." ”

“ In the lamp one of the carbon-holders is rigidly fixed to the framing of the apparatus, and the other is mounted on a point so as to enable the length of the arc playing over the clay cylinder to be regulated by the action of an electro-magnet attracting an armature in opposition to the tension of an adjustable spring. ”