Images of the fully shielded luminaire used in Brno (type Victor, made by Thorn). I've used the luminare also for documenting the change of the spectrum of a HPS lamp when starting.

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These are but details of the luminaire components. I've used a bit damaged fixture I borrowed from the Technology Networks Brno for a couple of days. Due to a slight deformation of the fixture body the glass did not touch perfectly the felt gasket.

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The first series of a start of an HPS lamp begins. The initial spectrum is that of a shining mercury vapour. The images have been taken by a HP315 digital camera through spectral glasses (no glass, just a diffraction grating, a foil with both vertical and horizontal grooves, for more see at the bottom).

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It became a low-pressure sodium now. The main yellow-orange line (a doublet of course, but too narrow to see it) becomes prominent, the colours are spoiled by the camera.

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The pressure rises and the main yellow-orange sodium line is no line anymore, growing thicker due to ``pressure broadening''.

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An absorption core in the already quite broad main sodium line develops. I suppose that it is produced by a layer of colder sodium vapour along the walls of the corund tube becoming optically thick in spite that it is geometrically very thin.

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Another lamp start begins, the first image has been to late to capture the mercury phase. LPS (low-pressure sodium) spectrum is the first one.

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This is already a true HPS (high-pressure sodium) spectrum, with the main line being a very broad one, spanning over several fainter lines which remained narrow.

The diffraction glasses I've used are sold for fun, but they are excellent for many purposes. They are a lot easier to use than CD to see all types of spectra around us. They can be ordered from Rainbow Symphony or from Edmund Scientifics (search for ``diffraction'') -- another diffraction foils and literature on using them and on spectra in general can be bought from there as well.

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