Luminous efficacy

K_cd = 683 lm W⁻¹

Unit: lm W⁻¹
Value: 683
Exact: yes
Note: Fixes the candela — the one SI base unit defined with human eyes in mind (555 nm green).
Symbol: K_cd
Category: Defining (SI)
Numeric: 683
Uncertainty: exact

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From the Constants database in Notion, last edited 2026-08-15. This page is the row, rendered by the build; nothing on it is written by hand.