Having grown up with a lot of WWII era radio tube displays in my dad's TV shop (he was a radar tech in the war) I would be really surprised if the actual screen background offered that much contrast. Most of the tubes I saw were very bright with a brighter sweep arc and the trailing fade and slightly lingering echo blip caused by the very slow response time of the early phosphor coatings. Television was still in its infancy and didn't look very good. Sometimes nearly impossible to tell what you were even looking at.
-Pv-
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