- Symbol
- Kcd
- Value
- 683
- Unit
- lm·W⁻¹
- Uncertainty
- exact (by definition)
- Copy-ready
683
Defines the candela, tying photometric units to radiant power.
NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.
The seven SI defining constants
Link to or cite this value
Link from a web page
Plain HTML for any page that accepts markup.
<a href="https://usephysics.com/reference/luminous-efficacy">Luminous efficacy of 540 THz radiation — 683 lm·W⁻¹ — UsePhysics</a>
Link from Markdown
For READMEs, wikis and notes.
[Luminous efficacy of 540 THz radiation — 683 lm·W⁻¹ — UsePhysics](https://usephysics.com/reference/luminous-efficacy)
Cite it in a document
Replace [date] with the day you consulted the page. The line credits NIST/CODATA for the values.
UsePhysics. "Luminous efficacy of 540 THz radiation — 683 lm·W⁻¹." UsePhysics.com. https://usephysics.com/reference/luminous-efficacy. Value from the 2022 CODATA adjustment (NIST). Accessed [date].