The laws list
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L to Lyman series.
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L.
L
See Avogadro constant.
Lambert's laws (J.H. Lambert)
Lambert's first law
The illuminance on a surface illuminated by light falling on it perpendicularly from a point source is proportional to the inverse square of the distance between the surface and the source.
Lambert's second law
If the rays meet the surface at an angle, then the illuminance is proportional to the cosine of the angle with the normal.
Lambert's third law
The luminous intensity of light decreases exponentially with distance as it travels through an absorbing medium.
Lagrange points
Points in the vicinity of two massive bodies (such as the Earth and the Moon) where each others' respective gravities balance. There are five, labelled L1 through L5. L1, L2, and L3 lie along the centerline between the centers of mass between the two masses; L1 is on the inward side of the secondary, L2 is on the outward side of the secondary; and L3 is on the outward side of the primary. L4 and L5, the so-called Trojan points, lie along the orbit of the secondary around the primary, sixty degrees ahead and behind of the secondary.

L1 through L3 are points of unstable equilibrium; any disturbance will move a test particle there out of the Lagrange point. L4 and L5 are points of stable equilibrium, provided that the mass of the secondary is less than about 1/24.96 the mass of the primary. These points are stable because centrifugal pseudoforces work against gravity to cancel it out.

Landauer's principle
A principle which states that it doesn't explicitly take energy to compute data, but rather it takes energy to erase any data, since erasure is an important step in computation.
Laplace equation (P. Laplace)
For steady-state heat conduction in one dimension, the temperature distribution is the solution to Laplace's equation, which states that the second derivative of temperature with respect to displacement is zero; mathematically,
d2 T/dr2 = 0.
Laue pattern (M. von Laue)
The pattern produced on a photographic film when high-frequency electromagnetic waves (such as x-rays) are fired at a crystalline solid.
laws of black-hole dynamics
See black-hole dynamic laws.
law of parismony
See Occam's razor.
laws of thermodynamics
See thermodynamic laws.
Lawson criterion (J.D. Lawson)
A condition for the release of energy from a thermonuclear reactor. It is usually stated as the minimum value for the product of the density of the fuel particles and the energy confinement time for energy breakeven. For a half-and-half mixture of deuterium and tritium at ignition temperature, nG tau is between 1014 and 1015 s/cm3.
Le Chatelier's principle (H. Le Chatelier; 1888)
If a system is in equilibrium, then any change imposed on the system tends to shift the equilibrium to reduce the effect of that applied change.
left-hand rule
The opposite-chirality version of the right-hand rule.
Lenz's law (H.F. Lenz; 1835)
An induced electric current always flows in such a direction that it opposes the change producing it.
Loschmidt constant; Loschmidt number; NL
The number of particles per unit volume of an ideal gas at standard temperature and pressure. It has the value 2.687 19 x 1025 m-3.
lumen; lm
The derived SI unit of luminous flux, defined as the luminous flux emitted by a uniform point source of 1 cd emitting its luminous energy over a solid angle of 1 sr; it thus has units of cd sr.
lumeniferous aether
A substance, which filled all the empty spaces between matter, which was used to explain what medium light was "waving" in. Now it has been discredited, as Maxwell's equations imply that electromagnetic radiation can propagate in a vacuum, since they are disturbances in the electromagnetic field rather than traditional waves in some substance, such as water waves.
lux; lx
The derived SI unit of illuminance equal to the illuminance produced by a luminous flux of 1 lm distributed uniformly over an area of 1 m2; it thus has units of lm/m2.
luxon
A particle which travels solely at c (the speed of light in vacuum). All luxons have a rest mass of exactly zero. Though they are massless, luxons do carry momentum. Photons are the prime example of luxons (the name itself is derived from the Latin word for light).

Compare tardon, tachyon.

Lyman series
The series which describes the emission spectrum of hydrogen when electrons are jumping to the ground state. All of the lines are in the ultraviolet.
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