Spotlit means lit by one strong beam picking it out. A spotlit stage, the spotlit painting, stand spotlit.
The rest going dark is the whole effect, and theatre uses it to tell an audience where to look. Museums light a single object this way for the same reason, and the heat and light are limited because both damage what is on show.
1adjectivespotlitLit by one strong beam picking it out.
“The singer stood alone on the spotlit stage while the rest of the hall was dark.”
spotlit is a quality of lighting.
spotlight comes from spot + light. From spot + light.
Etymology from Wiktionary, CC BY-SA
Practised in Light & Shadow, Shapes & Lines