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Molecular afterglow in a Philips SN lamp
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Philips introduced the SN lamps in the early 1980s mainly for image and video projection applications. These compact short-arc sources are filled with a mixture of tin halides (iodides, bromides and chlorides), complemented with small doses of indium and lithium halide for the emission of a well balanced light color at 5500 K. The molecular nature of the tin halide plasma excited between the electrodes result in a very diffuse light emission process which originates from tin mono-halide molecules (i.e., SnI and SnCl) that fill most of the burner volume (see picture below).
Interestingly, the tin halide vapor presents an exceptionally long afterglow decay time which is clearly visible for about ten seconds after the lamp is switched off (see main picture). Tin di-iodide molecules are thermally excited to one or several energy states from which they cannot (immediately) decay radiatively back to the ground state. In short, these molecules are brought to (long lived) metastable states from which they decay very slowly as the electron spin of these states flips and eventually enable a dipole-allowed transition to the ground level.
The resulting (very) long afterglow decay time results in a low flicker ratio - less than 20 % - of the emitted light during operation. This figure is very small compared to that of other conventional arc light sources, such as high-pressure mercury lamps (67 %). This characteristic was particularly valuable in video projection applications, especially since SN lamps were operated at 50 Hz from a conventional series choke ballast.
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Search![Molecular afterglow in a Philips SN lamp
Philips introduced the SN lamps in the early 1980s mainly for image and video projection applications. These compact short-arc sources are filled with a mixture of tin halides (iodides, bromides and chlorides), complemented with small doses of indium and lithium halide for the emission of a well balanced light color at 5500 K. The molecular nature of the tin halide plasma excited between the electrodes result in a very diffuse light emission process which originates from tin mono-halide molecules (i.e., SnI and SnCl) that fill most of the burner volume (see picture below).
[img]https://i.ibb.co/swp9Dg0/015.jpg[/img]
Interestingly, the tin halide vapor presents an exceptionally long afterglow decay time which is clearly visible for about ten seconds after the lamp is switched off (see main picture). Tin di-iodide molecules are thermally excited to one or several energy states from which they cannot (immediately) decay radiatively back to the ground state. In short, these molecules are brought to (long lived) metastable states from which they decay very slowly as the electron spin of these states flips and eventually enable a dipole-allowed transition to the ground level.
The resulting (very) long afterglow decay time results in a low flicker ratio - less than 20 % - of the emitted light during operation. This figure is very small compared to that of other conventional arc light sources, such as high-pressure mercury lamps (67 %). This characteristic was particularly valuable in video projection applications, especially since SN lamps were operated at 50 Hz from a conventional series choke ballast.
Keywords: Lamps](images/image.gif?id=496904177461 "Click to view full size image
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Molecular afterglow in a Philips SN lamp
Philips introduced the SN lamps in the early 1980s mainly for image and video projection applications. These compact short-arc sources are filled with a mixture of tin halides (iodides, bromides and chlorides), complemented with small doses of indium and lithium halide for the emission of a well balanced light color at 5500 K. The molecular nature of the tin halide plasma excited between the electrodes result in a very diffuse light emission process which originates from tin mono-halide molecules (i.e., SnI and SnCl) that fill most of the burner volume (see picture below).
[img]https://i.ibb.co/swp9Dg0/015.jpg[/img]
Interestingly, the tin halide vapor presents an exceptionally long afterglow decay time which is clearly visible for about ten seconds after the lamp is switched off (see main picture). Tin di-iodide molecules are thermally excited to one or several energy states from which they cannot (immediately) decay radiatively back to the ground state. In short, these molecules are brought to (long lived) metastable states from which they decay very slowly as the electron spin of these states flips and eventually enable a dipole-allowed transition to the ground level.
The resulting (very) long afterglow decay time results in a low flicker ratio - less than 20 % - of the emitted light during operation. This figure is very small compared to that of other conventional arc light sources, such as high-pressure mercury lamps (67 %). This characteristic was particularly valuable in video projection applications, especially since SN lamps were operated at 50 Hz from a conventional series choke ballast.
Keywords: Lamps")
