**Lambda, Λ, λ** (uppercase **Λ**, lowercase **λ**; Greek: λάμ(β)δα *lám(b)da*) is the 11th letter of the Greek alphabet. In the system of Greek numerals lambda has a value of 30. Lambda is related to the Phoenician letter Lamed . Letters in other alphabets that stemmed from lambda include the Latin L and the Cyrillic letter El (Л, л). The ancient grammarians and dramatists give evidence to the pronunciation as [laːbdaː] (λάβδα) in Classical Greek times.^{[1]} In Modern Greek the name of the letter, Λάμδα, is pronounced [lamða]; the spoken letter itself has the sound of "l" as with Latinate "L".

In early Greek alphabets, the shape and orientation of lambda varied.^{[2]} Most variants consisted of two straight strokes, one longer than the other, connected at their ends. The angle might be in the upper-left, lower-left ("Western" alphabets), or top ("Eastern" alphabets). Other variants had a vertical line with a horizontal or sloped stroke running to the right. With the general adoption of the Ionic alphabet, Greek settled on an angle at the top; the Romans put the angle at the lower-left.

The HTML 4 character entity references for the Greek capital and small letter lambda are "Λ" and "λ", respectively.^{[3]} The Unicode code points for lambda are U+039B and U+03BB.

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Examples of the symbolic use of uppercase lambda include:

- The lambda particle is a type of subatomic particle in subatomic particle physics.
- Lambda is the set of logical axioms in the axiomatic method of logical deduction in first-order logic.
- Lambda was used as a shield pattern by the Spartan army. This stood for Lacedaemon, (Λακεδαίμων,
*Lakedaímōn*), the name of the polis of the Spartans, as opposed to the city itself. - Lambda is the von Mangoldt function in mathematical number theory.
- In statistics, Wilks's lambda is used in multivariate analysis of variance (MANOVA analysis) to compare group means on a combination of dependent variables.
- In the spectral decomposition of matrices, lambda indicates the diagonal matrix of the eigenvalues of the matrix.
- In computer science, lambda is the time window over which a process is observed for determining the working memory set for a digital computer's virtual memory management.
- In astrophysics, lambda represents the likelihood that a small body will encounter a planet or a dwarf planet leading to a deflection of a significant magnitude. An object with a large value of lambda is expected to have cleared its neighborhood, satisfying the current definition of a planet.
- In crystal optics, lambda is used to represent the period of a lattice.
- In NATO military operations, a chevron (a capital lambda symbol) is painted on the vehicles of this military alliance for identification.
- In chemistry there are Δ (delta) and Λ (lambda) isomers, see: coordination complex
- In electrochemistry, lambda denotes the "equivalent conductance" of an electrolyte solution.
- In cosmology, lambda is the symbol for the cosmological constant, a term added to some dynamical equations to account for the acceleration of the universe.
- In optics, lambda denotes the grating pitch of a Bragg reflector.
- In block-handwritten Russian, this letter represents Л in both uppercase and lowercase.

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Examples of the symbolic use of lowercase lambda include:

- In evolutionary algorithms, λ indicates the number of offspring that would be generated from μ current population in each generation. The terms μ and λ are originated from Evolution strategy notation.
- Lambda indicates the wavelength of any wave, especially in physics, electronics engineering, and mathematics.
^{[4]} - Lambda indicates the radioactivity decay constant in nuclear physics and radioactivity. This constant is very simply related (by a multiplicative constant) to the half-life of any radioactive material.
- In probability theory, lambda represents the density of occurrences within a time interval, as modeled by the Poisson distribution.
- In mathematical logic and computer science, lambda is used to introduce anonymous functions expressed with the concepts of lambda calculus.
- Lambda is a unit of volume, synonymous with one microliter (1 μL), that is, one cubic millimetre (1 mm
^{3}). This use is currently deprecated. - Lambda indicates an eigenvalue in the mathematics of linear algebra.
- In the physics of electric fields, lambda sometimes indicates the linear charge density of a uniform line of electric charge (measured in coulombs per meter).
- Lambda denotes a Lagrange multiplier in multi-dimensional calculus.
- In solid-state electronics, lambda indicates the channel length modulation parameter of a MOSFET.
- There is a lambda phage virus in biology.
- In ecology, lambda denotes the long-term intrinsic growth rate of a population. This value is often calculated as the dominant eigenvalue of the age/size class matrix (mathematics).
- In formal language theory and in computer science, lambda denotes the empty string.
- Lambda is a nonstandard symbol in the International Phonetic Alphabet.
- In telecommunications, lambda indicates the wavelength in a wavelength-division multiplexing optical communications system. This is actually a form of the long-established concept of frequency-division multiplexing.
- Lambda denotes the Lebesgue measure in mathematical set theory.
- The Goodman and Kruskal's lambda in statistics indicates the proportional reduction in error when one variable's values are used to predict the values of another variable.
- Lambda denotes the oxygen sensor in a vehicle that measures the air-to-fuel ratio in the exhaust gases of an internal-combustion engine.
- A Lambda 4S solid-fuel rocket was used to launch Japan's first orbital satellite in 1970.
^{[5]} - Lambda denotes the failure rate of devices and systems in reliability theory, and it is measured in failure events per hour. Numerically, this lambda is also the reciprocal of the mean time between failures.
- In criminology, lambda denotes an individual's frequency of offenses.
- In cartography and navigation, lambda denotes the longitude of a location.
- Lambda denotes Christopher Langton's parameter for the classification of Stephen Wolfram's classes of cellular automata.
- In electrochemistry, lambda also denotes the ionic conductance of a given ion (The composition of the ion is generally shown as a subscript to the lambda character).
- In neurobiology, lambda denotes the length constant (or exponential rate of decay) of the electric potential across the cell membrane along a length of a nerve cell's axon.
- In the science and technology of heat transfer, lambda denotes the heat of vaporization per mole of material (a.k.a. its "latent heat").
^{[6]} - In the technology and science of celestial navigation, lambda denotes the longitude as opposed to the Roman letter "L", which denotes the latitude.
- King Louis XIII of France used the letter lambda as his personal symbol rather than a monogram.
- In Volvo automobiles, lambda denotes an engine, fuel, or ignition system failure.
- A block style Lambda is used as a recurring symbol in the Valve Corporation computer game series
*Half-Life*,^{[7]}referring to the Lambda complex of the fictional Black Mesa Research Facility, as well as making appearances in the sequel*Half-Life 2*.^{[8]}

The Roman *libra* and Byzantine *lítra* (λίτρα), which served as both the pound mass unit and liter volume unit, were abbreviated in Greek using lambda with modified forms of the iota subscript (as λͅ). These are variously encoded in Unicode. The Ancient Greek Numbers Unicode block includes 10183 GREEK LITRA SIGN (𐆃) as well as 𐅢, which is described as 10162 GREEK ACROPHONIC HERMIONIAN TEN^{[9]} but was much more common as a form of the litra sign. A variant of the sign can be formed from 0338 COMBINING LONG SOLIDUS OVERLAY and either 039B GREEK CAPITAL LETTER LAMDA (Λ̸) or 03BB GREEK SMALL LETTER LAMDA (λ̸).^{[10]}

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- Stargate SG-1 uses a modified upper-case lambda, with a small circle above the apex, to indicate Earth. This symbol has since become associated with the entire franchise.
^{[11]}^{[12]} - Brothers of the Lambda Theta Phi Latin Fraternity are considered Lambda Men, or simply Lambdas.
- Brothers of the Lambda Phi Epsilon Asian American interest fraternity are commonly referred to as Lambdas.
- Lambda is occasionally used in graphic design to represent a stylised "A".
- Several LGBT rights organizations, such as Lambda Legal and the Lambda Literary Award, derive their names from the use of a lower-case lambda as a symbol for LGBT rights.
- An automotive oxygen sensor (O
_{2}sensor) is also known as a lambda probe, sensor, sond, or sonde. - Lambda is used in art and photography to refer to a digital Type C print, or to the equipment that is used to produce it.
- In the study of gasoline engines, lambda sometimes refers to the air–fuel mixture going into the engine.
^{[13]}

Unicode uses the spelling "lamda" in character names, instead of "lambda", due to "preferences expressed by the Greek National Body".^{[14]}

- Greek Lambda / Coptic Laula

Character | Λ | λ | ᴧ | Ⲗ | ⲗ | |||||
---|---|---|---|---|---|---|---|---|---|---|

Unicode name |
GREEK CAPITAL LETTER LAMDA | GREEK SMALL LETTER LAMDA | GREEK LETTER SMALL CAPITAL LAMDA | COPTIC CAPITAL LETTER LAULA | COPTIC SMALL LETTER LAULA | |||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 923 | U+039B | 955 | U+03BB | 7463 | U+1D27 | 11414 | U+2C96 | 11415 | U+2C97 |

UTF-8 | 206 155 | CE 9B | 206 187 | CE BB | 225 180 167 | E1 B4 A7 | 226 178 150 | E2 B2 96 | 226 178 151 | E2 B2 97 |

Numeric character reference | Λ | Λ | λ | λ | ᴧ | ᴧ | Ⲗ | Ⲗ | ⲗ | ⲗ |

Named character reference | Λ | λ | ||||||||

DOS Greek | 138 | 8A | 162 | A2 | ||||||

DOS Greek-2 | 182 | B6 | 229 | E5 | ||||||

Windows 1253 | 203 | CB | 235 | EB | ||||||

TeX | \Lambda | \lambda |

- Mathematical Lambda

Character | 𝚲 | 𝛌 | 𝛬 | 𝜆 | 𝜦 | 𝝀 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

Unicode name |
MATHEMATICAL BOLD CAPITAL LAMDA |
MATHEMATICAL BOLD SMALL LAMDA |
MATHEMATICAL ITALIC CAPITAL LAMDA |
MATHEMATICAL ITALIC SMALL LAMDA |
MATHEMATICAL BOLD ITALIC CAPITAL LAMDA |
MATHEMATICAL BOLD ITALIC SMALL LAMDA |
||||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120498 | U+1D6B2 | 120524 | U+1D6CC | 120556 | U+1D6EC | 120582 | U+1D706 | 120614 | U+1D726 | 120640 | U+1D740 |

UTF-8 | 240 157 154 178 | F0 9D 9A B2 | 240 157 155 140 | F0 9D 9B 8C | 240 157 155 172 | F0 9D 9B AC | 240 157 156 134 | F0 9D 9C 86 | 240 157 156 166 | F0 9D 9C A6 | 240 157 157 128 | F0 9D 9D 80 |

UTF-16 | 55349 57010 | D835 DEB2 | 55349 57036 | D835 DECC | 55349 57068 | D835 DEEC | 55349 57094 | D835 DF06 | 55349 57126 | D835 DF26 | 55349 57152 | D835 DF40 |

Numeric character reference | 𝚲 | 𝚲 | 𝛌 | 𝛌 | 𝛬 | 𝛬 | 𝜆 | 𝜆 | 𝜦 | 𝜦 | 𝝀 | 𝝀 |

Character | 𝝠 | 𝝺 | 𝞚 | 𝞴 | ||||
---|---|---|---|---|---|---|---|---|

Unicode name |
MATHEMATICAL SANS-SERIF BOLD CAPITAL LAMDA |
MATHEMATICAL SANS-SERIF BOLD SMALL LAMDA |
MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL LAMDA |
MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL LAMDA |
||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120672 | U+1D760 | 120698 | U+1D77A | 120730 | U+1D79A | 120756 | U+1D7B4 |

UTF-8 | 240 157 157 160 | F0 9D 9D A0 | 240 157 157 186 | F0 9D 9D BA | 240 157 158 154 | F0 9D 9E 9A | 240 157 158 180 | F0 9D 9E B4 |

UTF-16 | 55349 57184 | D835 DF60 | 55349 57210 | D835 DF7A | 55349 57242 | D835 DF9A | 55349 57268 | D835 DFB4 |

Numeric character reference | 𝝠 | 𝝠 | 𝝺 | 𝝺 | 𝞚 | 𝞚 | 𝞴 | 𝞴 |

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.

Look up or Λ in Wiktionary, the free dictionary.λ |

- El (Cyrillic) – Л, л
- Fraser alphabet#Consonants
- Greek letters used in mathematics, science, and engineering

**^**Herbert Weir Smyth.*A Greek Grammar for Colleges*. I.1.c**^**"Epigraphic Sources for Early Greek Writing".*Poinikastas.csad.ox.ac.uk*. Retrieved 2011-10-03.**^**World Wide Web Consortium W3C.*HTML 4.01 Specification*,*24. Character entity references in HTML 4*. [1]**^**Nelkon, Michael (1977).*Fundamentals of Physics*. St. Albans, Hertfordshire: Hart-Davis Educational. p. 329.**^**"Encyclopedia Astronautica: Lambda".*Astronautix.com*. Archived from the original on 2012-10-22. Retrieved 2012-12-18.**^**Wankat Separation Process Engineering 2nd ed, Prentice Hall**^**"Half-Life on Steam".*store.steampowered.com*. Valve. Retrieved 2017-01-02.**^**"Half-Life 2 on Steam".*store.steampowered.com*. Valve. Retrieved 2017-01-02.**^**Unicode Ancient Greek Numbers block.**^**"Thesaurus Linguae Graecae" (PDF).*Stephanus.TLG.UCI.edu*. Archived from the original (PDF) on 2011-07-16.**^**Read, David (July 15, 2010). "Earth Symbol". Propworx. Archived from the original on September 19, 2010. Retrieved 2010-10-12.**^**"Official Stargate Website". Metro-Goldwyn-Mayer. Retrieved 2010-10-13.**^**Balich, Garrett; Aschenbach, Conrad (4 May 2004).*The Gasoline 4-Stroke Engine for Automobiles*(PDF). Notre Dame, Indiana: Department of Aerospace and Mechanical Engineering University of Notre Dame. p. 37. Archived from the original (PDF) on 8 October 2016. Retrieved 27 September 2016.**^**https://www.unicode.org/mail-arch/unicode-ml/y2010-m06/0063.html