Lysbuelampe
En lysbuelampe er en lampe, der producerer lys via en lysbue. Lampen består af to elektroder, der i moderne lamper typisk lavet af wolfram, der er adskilt af en luftart (fx neon eller xenon). Før glødepærer blev almindelige, benyttedes lysbuelamper med kulelektroder, såkaldte kulbuelamper. I disse brænder lysbuen i almindelig luft.
Humphry Davy opfandt lysbuelampen i 1800'erne. Den elektriske strøm i lampen er kraftig, men spændingen er ikke så høj, så for at tænde lampen skal de to kulelektroder kortvarigt føres sammen, hvorved kredsløbet sluttes og buen tændes. Derefter trækkes kullene fra hinanden. Størstedelen af lyset stammer fra de glødende kulspidser. Automatiske mekanismer kan evt. regulere elektrodeafstanden, efterhånden som kullene fortæres og strømmen ændres.
En særlig kulbuelampe, Jablokovs kærte, kræver ikke nogen mekanik til at justere elektrodeafstanden, da kullene er parallelle og fortæres oppefra og ned. Til gengæld kræves der et lille stykke grafit, der forbinder de to kul, for at tænde lampen. Grafitstykket fordamper hurtigt. Den er derfor vanskelig at tænde, når den først en gang har været slukket.
Lysstyrken var ideel til fx gadelys, men for kraftig til almindelig indendørs belysning. Lysbuelamper har desuden været benyttet i lyskastere og i filmprojektorer, hvor det kraftige lys var nødvendigt. Lysbuelamper danner en del ultraviolet lys.
Kilder og henvisninger
- Opvarmning og Belysning i Menneskeaandens Sejre – København 1904 / Poul la Cour og Helge Holst
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Medier brugt på denne side
Forfatter/Opretter: D-Kuru, Licens: CC BY-SA 3.0 at
An arc lamp during ignition
(c) Atlant, CC BY 2.5
Close-up of a 15KW Xenon short-arc lamp. See also end view.
The candle by Jablochkoff consists of two parallel carbon rods a b (Fig. 499), which are separated from each other by a layer of plaster of Paris ; the lower portions of the carbons have short brass tubes fastened to a plate A, against which two metal springs e and g press, and the current is conducted through the latter into the candle. A thin plate of graphite c is laid across the two carbon points, and is held in position by a paper band d, which serves also to light the candle. When the candle is inserted in the circuit a current passes from one of the carbon rods through the connecting piece at the top to the second carbon rod, and then back again to the source of electricity. The connecting piece becomes heated, and after it has been volatilised helps to form the arc between the two carbon rods. As the carbons are consumed the insulating layer is made to fuse and to volatilise. Since the positive carbon is consumed twice as quickly as the negative, it must have twice the cross section of the negative. This proportion is, however, not exact, and as all candles are not consumed at exactly the same rate, alternating currents have to be used. A candle, the carbon rods of which have a cross section of four millimetres, and a length of from 220 to 225 millimetres, burns about 1 ½ hours, producing a light of 100-candle power. Several candles can be inserted in one circuit, the light intensity of the sum of the candles being greater than that of a correspondingly large single candle. The reason of this is, that not only is the voltaic arc between the two carbons luminous, but so also is the volatilising substance between the carbons. When from two to five candles are inserted in one circuit, by turning a commutator one candle after another may be lighted. This arrangement is very inconvenient, and if one of the candles should go out from some cause, all the other candles in the same circuit would go out too, and could only be relighted by turning their respective commutators.