The natural color of the VFD is blue-green, ie the intensity of the light output is greatest in the blue-green part of the visible light spectrum. So if you use a filter that matches somewhere in this range, ie, light blue, or light green, you will get more light out of it than if you try to use a filter that doesn't, eg red. To get a red display from the VFD, the filter has to cut out all of the blue/green light, leaving only the red component of the light, which isn't very much. Amber is similar.
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Mk2a 60GB Blue. Serial 030102962
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