How do xenon electric flash lamps work?

16 Июн 2014 | Author: | Комментарии к записи How do xenon electric flash lamps work? отключены
Noble Electric Cars

Xenon lamps and arc lamps

by Chris Woodford. Last updated: November 16, 2013.

Y ou may have only a fraction of a second to catch a vital photograph. but what if it’s too dark to see? Flash lamps, filled with a gas called xenon . are the answer. Press the button on your camera, wait a few moments for the flash to charge, hit the shutter button to take your picture andCRACK!you suddenly have all the light you need. What exactly are xenon lamps and how do they work? They’re examples of what we call arc lamps and they work in a very different way to ordinary lamps.

Let’s take a closer look!

Photo: Lighthouse lamp: It takes an extremely bright light to throw a beam miles out to sea, even with the help of a powerful Fresnel lens (the concentric circles you can see in the background). That’s why many lighthouses are powered by super-bright xenon lamps. Photo by Gary Nichols courtesy of US Navy .

How do xenon lamps work?

All lamps make light, but they don’t all work the same way. Incandescent lamps (our traditional household lights) make light by passing electricity through a thin metal filament (wire), so it gets really hot and burns brightly. Fluorescent lamps are very different: they zap electricity through a gas to make invisible ultraviolet light. which gets converted into light we can see (visible light) when it passes through the white inner coating of the lamp’s glass tube, making it glow brightly (or fluoresce ).

Like neon lamps. xenon lamps are examples of arc lamps . An arc lamp is a bit like a small bolt of lightning happening under very controlled conditions inside a glass tube filled with a gas under either very low or very high pressure (depending on the type of lamp). At the two ends of the tube there are metal contacts called electrodes, connected to a high-voltage power supply.

Where does the light come from? When the power supply is turned on, the gas atoms suddenly find themselves under incredible, electrical force and split into smaller parts. This is called ionization (or ionizing the gas). The broken bits of atoms (positively charged ions and negatively charged electrons) then hurtle in opposite directions along the tube, with electrons rushing to the positive electrode and ions going the other way, forming an electric current. The ions and electrodes crash into one another and into the electrodes, giving off energy as a flash of light called an arc that effectively leaps the gap between the electrodesjust like a lightning bolt.

More light is produced by the electrodes themselves, which become incredibly hot and burn brightly in the process. Temperatures of over 3000C or 5400F are typical, which is why the electrodes are generally made of tungsten. the metal with the highest melting point (approximately 3400C or 6200F). The color of the light depends on the atomic structure of the gas that’s used (we explain this in more detail in our article on neon lamps ). In a neon lamp, the light produced is red; in a xenon lamp, it’s a blueish, grayish, whiteish light not that different from natural daylight.

Photo: Electric arcs generate so much heat and such high temperatures that they can also be used to weld metals together. This is known as arc welding. Picture taken at Idaho National Laboratory, Idaho Falls, courtesy of US Department of Energy (DOE Photo).

How arc lamps work

Strictly speaking, we use the term arc lamp to mean one, particular type of arc lamp with carbon electrodes and air in between them. Before Edison, Swan, and their contemporaries perfected the incandescent lamp. arc lamps like this were really the only type of electric light available. They were invented in 1807 (about 70 years before Edison perfected his lamp) by British chemist Sir Humphry Davy (17781829).

Davy found he could make electric light by connecting two carbon electrodes (a bit like pencils) to a high-voltage power supply. Initially, he kept the electrodes touching one another. Gradually, as he moved them apart, he found an arch-shaped beam of light spanning the gap between themwhich is how arc lamps got their name. Arc lamps weren’t very practical: they needed huge electric current to make them work and the high temperature of the arc quickly burned the carbon electrodes away in the air.

Huge electric current is no exaggeration: Davy had to use a battery with 2000 separate cells to make a 10cm (4-inch) arc.

Modern incandescent lamps developed when arc lamps were improved in two ways. The air gap was replaced by a filament, so lower voltages and currents could be used. The whole lamp was also sealed inside a glass bulb filled with a noble gas to prevent the filament from burning up in the air’s oxygen.

That made the lamp last very much longer.

Photo: The basic concept of the arc lamp. An electric discharge passes between two carbon electrodes, giving off light.

What are the different kinds of xenon lamps?

In xenon photographic flash lamps, the light is literally a flash: it lasts anything from a microsecond (one millionth of a second) to about a twentieth of a second. There’s no real need for it to last any longer since it only takes this long to capture a photo. Other kinds of xenon lamps work more like neon lamps and produce smaller amounts of light continually.

Instead of passing a huge amount of electricity through the gas very briefly to produce a sudden arc of light, they use smaller, steadier voltages to produce a constant discharge of bright light. Movie-projector lamps, lighthouse lamps, and HID (high-intensity discharge) car headlamps are all examples of xenon lamps that work in this way.

Photo: Here’s a very small xenon flash lamp from inside a digital camera. The black and red wires connect the two electrodes at opposite ends of the lamp to a capacitor (the black cylinder just visible on the top left). The capacitor’s job is to build up a high-voltage charge that’s big enough to make a discharge in the flash tube using only the camera’s puny, low-voltage batteries.

That takes timewhich is why you often have to wait a few seconds to take a flash photo. The camera lens is the black circle underneath the flash. Flash lamps that work this way were invented in 1931 by American electrical engineer and photographer Harold E. Edgerton (19031990).

What is xenon anyway?

You’ve heard of neon? Xenon is similar. Helium, neon, argon, krypton, xenon, and radon are the chemical elements from the part of the periodic table that we call the noble gases (once called the inert gases because they don’t really react that well with other elements).

If you think back to your school chemistry, the noble gases are the elements down the column on the extreme right.

What’s xenon like? It has no color, taste, or smell, but it is present in the air around us in minutely small quantitiesroughly one molecule of xenon for every 20 million molecules of other gases. Xenon atoms have an atomic number of 54 (much heavier than oxygen or nitrogen atoms), so xenon gas is about 4½ times heavier than air: if you’re hunting for xenon, look near the ground!

Xenon is a gas on Earth because it melts at roughly −111C (−168F) and boils at −107C (−161F).

Artwork: The periodic table of chemical elements showing the position of xenon. Notice how it’s over on the right with the noble gases and toward the bottom of group 18. That tells you that xenon atoms are relatively heavy, which is why xenon gas is heavier than air.

Artwork courtesy of NASA (with modifications).

Who discovered xenon?


Most of the noble gases, including xenon, were discovered by Scottish chemist Sir William Ramsay (18521916), who won the Nobel Prize in Chemistry in 1904 for his work. According to the Royal Swedish Academy of Sciences, which awarded the prize: The discovery of an entirely new group of elements, of which no single representative had been known with any certainty, is something utterly unique in the history of chemistry, being intrinsically an advance in science of peculiar significance. The more remarkable is this advance when we recollect that all these elements are components of the atmosphere of the earth, and that, though apparently so accessible for scientific research, they have for so long a time baffled the acumen of eminent scientists.

Quoted from Presentation Speech by Professor J.E. Cederblom. President of the Royal Swedish Academy of Sciences, on December 10, 1904.

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