Response of inert gasses to pulsed vs constant energy

Factual Questions
1

Strange question.

It seems that Xenon lamps provided with a 1µs pulse of voltage efficiently transform this to light. However, when given constant voltage, the short wavelength emmitted drops dramatically.

Why? Do all of the inert gasses have some charateristic pulse duration at which they provide optimal wavelength emittance? I’ve just encountered this effect and I’m not even sure what I’m looking for (re: googling).

Thanks…

2

Says who? What’s meant by “constant” voltage?

If the phenomenon you mention is real, it must have been discovered during a very interesting experiment! If you dump a joule of energy into a strobe tube as a one microsecond pulse, that’s a million watts. The total energy is small, so the tube is only slightly warm after the megawatt pulse. If you put the same voltage across the strobe tube “continuously”, it would put out a megawatt continuously, and the tube would detonate like a bomb (and possibly set fire to everything exposed to the megawatt light output in the milliseconds before the tube was destroyed.)

With continuous output, the xenon gas would become fantastically hot in a very short time, which would certainly change the wavelengths of light being emitted. But the same would happen with any gas discharge, not just xenon.

3

Here’s a 30,000 watt continuous output Xenon arc lamp. It’s not anywhere near a megawatt, but still the electrodes require a liquid cooling system.

4

Then this is the answer to my question.

5

Um, you meant intensity of the wavelengths, right? Characteristic emmission is characteristic emmission, is it not?

6

If it becomes fantastically hot, you’ll get blackbody radiation, like an incandescent light bulb, not just the characteristic emission.

7

Well, it’s not quite that simple… The characteristic emmission depends on several parameters. (Or rather, it depends only on the electron energy levels. They in turn depend on other parameters.)

For a good example, look at a high pressure sodium lamp! When it starts up, it has the intensive yellow spectrum, that we expect from sodium, but once it heats up the gas, the spectrum becomes a lot more ‘white’.

(What happens is that the distinct energy levels we all know from physics classes become separated into so many different levels, that it makes more sense to talk about a band. Atoms in the gas will absorb photons of any energy within this gap, and maybe change their internal energy slightly, before emitting a new photon at a slightly different energy. )