Clear blue (argon, with mercury, in clear glass) is nowhere near as bright as the white tubes that glow blue, why is that?
Argon produces much more ultra violet than visible light. In a phosphorus coated tube, the U.V. light momentarily induces the atoms of the phosphorous coating into a super excited state (the electrons move out one electron shell) when the electrons return their normal state they re release the absorbed energy at a lower form, in the form of visible light. Note: clear tubes are not a danger because the glass itself absorbs most of the U.V. light.
