Physical world and mathematics

LDN 1495

LDN 1495, also written L1495 or Lynds 1495, is a large dark nebula in the Taurus Molecular Cloud about 450 light years away, a heavily studied star-forming filament.

LDN 1527

LDN 1527 is a dark nebula in the Taurus molecular cloud, about 460 light-years away, hosting the protostar L1527 IRS, imaged by JWST in 2022.

LDN 1544

LDN 1544 (also L1544) is a dark nebula in Taurus, in the Taurus Molecular Cloud, containing one of astronomy's most studied pre-stellar cores about to form a star.

LDN 1551

LDN 1551 is a dark molecular cloud in Taurus about 160 parsecs away, where the protostar L1551 IRS 5 hosted the first recognized bipolar molecular outflow, detected in 1980.

LDN 1630

LDN 1630, also written Lynds 1630, is a large dark nebula in Orion, cataloged by Beverly T. Lynds in 1962 and identical to the Orion B molecular cloud.

LDN 1641

LDN 1641, also written Lynds 1641 or L1641, is a dark molecular cloud in Orion forming the southern part of the Orion A molecular cloud.

Le Chatelier's principle

Le Chatelier's principle, also called the Le Chatelier-Braun principle, states that an equilibrium system shifts to counteract a change in conditions, proposed by Henry-Louis Le Chatelier in 1884.

Le Sage's theory of gravitation

Le Sage's theory of gravitation, also known as push gravity, is a mechanical explanation of gravity, proposed by Georges-Louis Le Sage of Geneva in the 18th century.

Sep 21, 2026

Lea Nienhaus is a chemist known for solid-state perovskite-sensitized photon upconversion, turning infrared light into visible light; she has been an associate professor at Rice University since 2024.

Leaching (chemistry)

Leaching, also called lixiviation, is the transfer of a soluble substance from a solid into a liquid, used in metal extraction and studied as an environmental contaminant pathway.

Sep 29, 2026

Leaching test

A leaching test is a standardized laboratory procedure that contacts a solid with a liquid and measures which constituents dissolve out, to assess environmental mobility of contaminants.

Lead

Lead (symbol Pb, from the Latin plumbum) is a soft, dense, dull silvery-gray post-transition metal with atomic number 82, mined for more than 6,000 years.

Lead chloride

Lead chloride (PbCl₂) is a white crystalline lead compound, found in nature as the volcanic mineral cotunnite and used in lead recovery and perovskite solar cells.

Lead chromate

Lead chromate (PbCrO₄) is an inorganic compound found in nature as the red-orange mineral crocoite and used industrially as the chrome yellow pigments, whose lead and hexavalent chromium content has made them tightly regulated.

Lead dioxide

Lead dioxide, also called lead peroxide, is a dark-brown, insoluble oxide of lead in the +4 oxidation state that serves as the positive-plate active material of lead-acid batteries.

Lead glass

Lead glass, also known as lead crystal, is glass containing at least 20 percent lead oxide, prized for its brilliance and used in tableware and radiation shielding.

Lead glass hot cell window

A lead glass hot cell window is a thick, lead-oxide-bearing viewing window installed in a hot cell wall, shielding operators watching remote handling of radioactive materials.

Lead halide perovskite

A lead halide perovskite is a semiconductor with the ABX₃ crystal formula, combining strong absorption and defect tolerance with low-cost solution processing; solar cells reached 27.2% efficiency in 2025.

Lead line (nautical)

A lead line, also called a sounding line, is a marked rope with a lead weight used for centuries to measure water depth and sample the seabed.

Lead oxide

Lead oxide is the family of lead–oxygen compounds, including lead monoxide (litharge or massicot), red lead, and lead dioxide, used for millennia in silver refining, batteries, glass, and pigments.

Lead paint

Lead paint is paint containing lead, a toxic metal, used for centuries and banned for US residential use in 1978 because it causes lead poisoning.

Lead shielding

Lead shielding is the use of lead as a barrier material to attenuate ionizing radiation, most commonly gamma rays and X rays, between a source and people.

Lead sulfate

Lead sulfate (PbSO₄) is an inorganic salt of lead(II) and sulfate that forms at both electrodes when a lead-acid battery discharges; its buildup causes sulfation.

Lead zirconate titanate

Lead zirconate titanate (PZT), a ceramic solid solution of lead zirconate and lead titanate discovered in 1953, is the most widely used piezoelectric ceramic in commercial electronics.

Lead-210

Lead-210 (²¹⁰Pb) is a radioactive isotope of lead with a half-life of about 22.3 years, formed in the uranium-238 decay series and used to date recent sediments and snow.

Lead-210 dating

Lead-210 dating is a radiometric method that determines the age of recent sediments, ice, and peat by measuring decay of lead-210, covering about 100 to 150 years.

Lead-212

Lead-212 (²¹²Pb, historically thorium B) is a radioactive lead isotope with a 10.64-hour half-life that decays to alpha-emitting bismuth-212, used in nuclear medicine for targeted alpha therapy of cancer.

Lead-free double perovskites

Lead-free double perovskites are halide semiconductors of formula A₂B⁺B³⁺X₆ in which two lead ions are replaced by monovalent and trivalent cations, studied as stable, nontoxic alternatives to lead-halide perovskites for solar cells, detectors, and LEDs.

Lead-free perovskite nanocrystals

Lead-free perovskite nanocrystals are nanoscale semiconductor crystals with the perovskite structure in which toxic lead is replaced by less-toxic metals such as Sn, Ge, Sb, and Bi.