Etymology
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luminous (adj.)
early 15c., "full of light, shiny," from Latin luminosus "shining, full of light, conspicuous," from lumen (genitive luminis) "light," from suffixed form of PIE root *leuk- "light, brightness." Related: Luminously; luminousness.
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luminosity (n.)
1630s, "quality of being luminous," from French luminosité (cognate with Medieval Latin luminositas "splendor") or else a native formation from luminous + -ity. Meaning "intensity of light in a color" (of a flame, spectrum, etc.) is from 1876. In astronomy, "intrinsic brightness of a heavenly body" (as distinguished from apparent magnitude, which diminishes with distance), attested from 1906.
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*leuk- 

Proto-Indo-European root meaning "light, brightness."

It forms all or part of: allumette; elucidate; illumination; illustration; lea; leukemia; leuko-; light (n.) "brightness, radiant energy;" lightning; limn; link (n.2) "torch of pitch, tow, etc.;" lucent; lucid; Lucifer; luciferase; luciferous; lucifugous; lucubrate; lucubration; luculent; lumen; Luminal; luminary; luminate; luminescence; luminous; luna; lunacy; lunar; Lunarian; lunate; lunation; lunatic; lune; lunette; luni-; luster; lustrum; lux; pellucid; sublunary; translucent.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit rocate "shines;" Armenian lois "light," lusin "moon;" Greek leukos "bright, shining, white;" Latin lucere "to shine," lux "light," lucidus "clear;" Old Church Slavonic luci "light;" Lithuanian laukas "pale;" Welsh llug "gleam, glimmer;" Old Irish loche "lightning," luchair "brightness;" Hittite lukezi "is bright;" Old English leht, leoht "light, daylight; spiritual illumination," German Licht, Gothic liuhaþ "light."

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candela (n.)
unit of luminous intensity, 1950, from Latin candela "a light, torch, candle made of tallow or wax" (see candle).
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sea-green (n.)

as a color, a luminous, pale bluish-green, 1590s, from sea + green (adj.). As an adjective from c. 1600. Sea-green incorruptible was Carlyle's term for Robespierre.

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luculent (adj.)

early 15c., "luminous, bright;" 1590s, "evident, lucid," from Latin luculentus "full of light, bright, splendid," from the stem of lux "light" (from PIE root *leuk- "light, brightness").

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phosphorescent (adj.)

shining with a faint light or luminosity like that of phosphorus, luminous without sensible heat," "1766, from Modern Latin phosphorus (see phosphorus) + -escent. Related: Phosphorescently.

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photosphere (n.)

1660s, "orb of light, envelop of light," from photo- "light" + sphere. Astronomical sense "luminous envelop around the sun (or another star)" is from 1848. Related: Photospheric.

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lucent (adj.)
mid-15c., "shining, bright, luminous," from Latin lucentem (nominative lucens), present participle of lucere "to shine, glow, be bright," from PIE root *leuk- "light, brightness." Meaning "translucent, clear" is from 1820. Related: Lucently.
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phosphorescence (n.)

"a property of certain bodies of becoming luminous without undergoing combustion," 1796, from French phosphorescence (1788) or from the English verb phosphoresce "emit luminosity without combustion" (1794; see phosphorous) + -ence.

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