Etymology
Advertisement
phosphene (n.)

"the luminous ring produced by pressing the eyeball with the finger, etc.," 1872, from French phosphène, irregularly formed from Greek phōs "light" + phainein "to show," both from PIE root *bha- (1) "to shine."

Related entries & more 
Advertisement
quasar (n.)

1964, from "quas(i-stell)ar radio source" (1963); see quasi- + stellar. So called because they resembled stars in photographic images; now thought to be massive, distant, extremely luminous active galactic nuclei.

Related entries & more 
penumbra (n.)

1660s, "partially shaded region around the shadow of an opaque body, a partial shadow," from Modern Latin penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from Latin pæne "nearly, almost, practically," which is of uncertain origin, + umbra "shadow" (see umbrage). Figurative use is by 1801. Related: Penumbral.

All points within the penumbra are excluded from the view of some part of the luminous body, and are thus partially shaded; while all points within the umbra, or total shadow, are completely excluded from view of the luminous body. [Century Dictionary]
Related entries & more 
firefly (n.)

also fire-fly, "An insect which has the faculty of becoming luminous" [Century Dictionary], 1650s, from fire (n.) + fly (n.). Ancient Greek had kysolampis "firefly, beetle with a tail that lights up at night," from kysos, kysthos "buttocks" + lampein "to shine."  

Related entries & more 
aureole (n.)
early 13c., "celestial crown worn by martyrs, virgins, etc., as victors over the flesh," from Latin aureola (corona), fem. diminutive of aureus "golden" (see aureate). In religious art aureola (1848) is the luminous cloud or aura surrounding holy figures.
Related entries & more 
Advertisement
dusky (adj.)

1550s, "somewhat dark, not luminous, dim;" see dusk + -y (2). "The normal source of an adj. in -y is a sb.; but the substantival use of dusk is not known so early as the appearance of dusky, so that the latter would appear to be one of the rare instances of a secondary adj. ..." [OED]. Meaning "rather black, dark-colored" is from 1570s. Related: Duskily; duskiness.

Related entries & more 
nebulous (adj.)

late 14c., "cloudy, misty, hazy" (of the eye, fire-smoke, etc.), from Latin nebulosus "cloudy, misty, foggy, full of vapor," from nebula "mist, vapor" (from PIE root *nebh- "cloud"). The figurative sense of "hazy, vague, formless" is attested by 1831. Astronomical sense, in reference to stars or star clusters surrounded by luminous haze, is from 1670s. Related: Nebulously; nebulousness.

Related entries & more 
incandescent (adj.)

"glowing with heat, rendered luminous by heat," 1794, from French incandescent (18c.) or directly from Latin incandescentem (nominative incandescens), present participle of incandescere "become warm, glow, kindle," from in- "within" (from PIE root *en "in") + candescere "begin to glow, become white," inceptive of candere "to glow, to shine" (from PIE root *kand- "to shine"). In reference to electric light, from 1881. The verb incandesce (1838), originally in science, is perhaps a back-formation.

Related entries & more 
light (adj.2)

"not dark," Old English leoht (West Saxon), leht (Anglian), "luminous, bright, beautiful, shining; having much light," from Proto-Germanic *leuhta- (source also of Old Saxon and Old High German lioht, Old Frisian liacht, German licht "bright"), from the source of Old English leoht (see light (n.)). Meaning "pale-hued" is from 1540s; prefixed to other color adjectives from early 15c. In earlier Middle English in reference to colors it meant "bright, vivid" (early 14c.).

Related entries & more 
dim (adj.)
Origin and meaning of dim

Old English dimm "dark, gloomy, obscure; not clearly seen, indistinct," from Proto-Germanic *dimbaz (source also of Old Norse dimmr, Old Frisian dim, Old High German timber "dark, black, somber"). Not known outside Germanic.

Of eyes, "not seeing clearly," early 13c. Of sound from early 14c.; of light, "not bright, faintly luminous," from early 14c. Modern slang sense of "dull of apprehension, stupid" is from 1892; the sense of "dull-witted" also was in Middle English (mid-13c.). Related: Dimly; dimness.

Related entries & more 

Page 2