Lambert (unit)

The lambert (symbol L, la or Lb) is a non-SI unit of luminance named for Johann Heinrich Lambert (1728–1777), a Swiss mathematician, physicist and astronomer. A related unit of luminance, the foot-lambert, is used in the lighting, cinema and flight simulation industries. The SI unit is the candela per square metre (cd/m²).

Definition

1 lambert (L) = $\frac{1}{\pi}$ candela per square centimetre (0.3183 cd/cm²) or $\frac{10^4}{\pi}$ cd m⁻²

See also

Other units of luminance:

• Apostilb (asb)
• Blondel (blondel)
• Bril (bril)
• Nit (nit)
• Stilb (sb)
• Skot (sk)

SI photometry quantities

Quantity		Unit		Dimension	Notes
Name	Symbolr	Name	Symbol	Symbol
Luminous energy	Qv	lumen second	lm⋅s	T⋅J	Units are sometimes called talbots.
Luminous flux / luminous power	Φv	lumen (= cd⋅sr)	lm	J	Luminous energy per unit time.
Luminous intensity	Iv	candela (= lm/sr)	cd	J	Luminous power per unit solid angle.
Luminance	Lv	candela per square metre	cd/m2	L−2⋅J	Luminous power per unit solid angle per unit projected source area. Units are sometimes called nits.
Illuminance	Ev	lux (= lm/m2)	lx	L−2⋅J	Luminous power incident on a surface.
Luminous exitance / luminous emittance	Mv	lux	lx	L−2⋅J	Luminous power emitted from a surface.
Luminous exposure	Hv	lux second	lx⋅s	L−2⋅T⋅J
Luminous energy density	ωv	lumen second per cubic metre	lm⋅s⋅m−3	L−3⋅T⋅J
Luminous efficacy	η	lumen per watt	lm/W	M−1⋅L−2⋅T3⋅J	Ratio of luminous flux to radiant flux or power consumption, depending on context.
Luminous efficiency / luminous coefficient	V			1
See also: SI · Photometry · Radiometry

References

• "Lighting Design Glossary: Luminance" at Schorsch Lighting Design Knowledgebase