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[qldbulls]

If the voltage of a vapour lamp providing a emission spectrum was increased, what would happen to light emitted?

I'm fairly sure that it would only increase light intensity: more photons of the particular emission spectra produced. There should be no change in frequency of emitted light.

If someone could confirm it would be much appreciated, the only issue is in the back of my mind I keep thinking about the voltage heating up the vapour like a black body which would produce a continuous spectrum which now that I type it is clearly incorrect but I'll put this up anyways just in case. Thank you

 

[carrotsss]

This might be wrong but im pretty sure vapour lamps emit a specific wavelength of light irrespective of voltage, so the frequency of photons wont change, only the intensity, so you're right.

 

[wizzkids]

Yep, agree. Think of the lamp as if it was an electrical resistor. The power output of the lamp is equal to the product of the voltage times the current. P = V x I. Assuming the resistance R of the ionised gas in the lamp is fairly constant, then P = V²/R
A small increase in the voltage will cause a big increase in the power output of the lamp.
OK, that's the electrical part dealt with.
So where does all this extra power go? The lamp will get hotter.
It will give out more emission photons per second. The wavelengths of the spectral lines of the lamp will not change. However, the distribution of those spectral lines may change. There may be more photons from the spectral lines that have shorter wavelength. Take neon gas for example. At low power, the spectrum of a Ne tube looks quite red, it consists of about four prominent red lines, but as the power increases the colour becomes brighter and a bit more orange as the shorter wavelength lines become more prominent. Here is a graph showing a gas that has four prominent emission lines in the red / orange / yellow part of the visible spectrum. The smooth curves represent the Maxwell-Boltzmann energy distribution for a hot gas at two different temperatures, 5000K and 6000K. At 5000K this gas has peak emission in the red part of its spectrum. At 6000K the same gas has peak emission in the orange part of its spectrum, so it's colour will look slightly different to the human eye. This is the effect of the Wein Displacement Law.