
die Leuchte
light
A device that produces light; a lamp including its socket, light source, and shade.
Wir haben eine neue Leuchte über dem Esstisch montiert.
We installed a new light above the dining table.
light / luminary
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light
A device that produces light; a lamp including its socket, light source, and shade.
Wir haben eine neue Leuchte über dem Esstisch montiert.
We installed a new light above the dining table.

luminary
A person who is exceptionally intelligent, capable, or well-known in a particular field; an authority.
Er gilt als eine echte Leuchte auf dem Gebiet der Astrophysik.
He is considered a true luminary in the field of astrophysics.
The noun 'die Leuchte' (the light/luminary) is derived directly from the verb 'leuchten' (to shine, to emit light). So a Leuchte is literally 'something that shines'.
Die Sterne leuchten heute Nacht besonders hell.
The stars are shining especially brightly tonight.
You can recognize the figurative meaning by the fact that a person is being discussed. It is usually mentioned in connection with a field of expertise, often with the phrase 'eine Leuchte auf dem Gebiet ... sein/gelten' (to be/be considered a luminary in the field of ...).
Professor Schmidt ist eine anerkannte Leuchte in der Genforschung.
Professor Schmidt is a recognized luminary in genetic research.
In connection with the physical object, verbs such as 'eine Leuchte anbringen' (to install a light), 'eine Leuchte montieren' (to mount/install a light), or 'eine Leuchte einschalten/ausschalten' (to switch a light on/off) are often used.
Kannst du bitte die Leuchte im Flur ausschalten?
Could you please switch off the light in the hallway?
Calling a person a 'Leuchte' (luminary) is rather elevated or educated language. It is often used approvingly, or sometimes slightly ironically.
Er hält sich für eine große Leuchte, aber seine Ideen sind nicht neu.
He thinks he's a great luminary, but his ideas aren't new.
lamp
Both words refer to a device that produces artificial light. „Lampe“ is the usual everyday term, especially for a single household lighting device; „Leuchte“ sounds more precise and technical and can also refer to permanently installed systems. In ordinary conversation, Lampe is usually the better choice; in technical specifications, Leuchte is more common.

Für den Flur wählt der Elektriker eine passende Leuchte aus.
The electrician is choosing a suitable light fixture for the hallway.
Für den Schreibtisch kaufe ich eine neue Lampe.
I’m buying a new lamp for my desk.