The lumen is NOT a base SI unit. The lumen describes the quantity of visible light emitted by a source per unit of time, and is a DERIVED unit based on the candela. The candela is the base unit in the SI system for luminous intensity. One lumen = 1 candela * sr (steradians).
From Wikipedia: “A full sphere has a solid angle of 4π steradians, so a light source that uniformly radiates one candela in all directions has a total luminous flux of 1 cd × 4π sr = 4π cd⋅sr ≈ 12.57 lumens.”
EDIT: Oh, you meant the candela itself! Sorry, I’m removing myself now…
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