It was the light panel from the jail in-"Return of the Archons" from the early Star Trek series. Later, Spock uses it to escape, shirtless
“Later, Spock uses it to escape, shirtless”
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It should probably disturb that I can rattle off the plot and some lines from these episodes, but it doesn’t...
(By the way, not shown in your pic - but Spock is standing on Kirk’s back to reach the light bulb and Kirk is telling him to hurry up because the guards did “a professional job” whipping his (Kirk’s) back.)