This will probably end up being a stupid question with a simple answer, but if you don't ask and just accept things then where's the understanding? Anyway, the spectrum of emission is usually shown as some form of Intensity vs Wavelength, my question is how does it relate to time and how is it measured? Does it vary with time or is it an instantaneous measurement of all the wavelengths emitted in the process? Does the wavelength change? I'm presently doing a dissertation on sonoluminescence and it occurred to me that my (very) basic knowledge of spectra is lacking, ive included a graph of the spectra for various gases (the gas in the bubble as it collapses and emits light) Any comments would be welcome! Thanks.