ETYM as. leóht. Related to Light.
1. Characterized by or emitting light.
2. (Used of color) Having a relatively small amount of coloring agent.
3. Not great in degree or quantity or number.
4. Of comparatively little physical weight or density.
5. Moving easily and quickly; nimble; SYN. lightsome, tripping.
6. Of little intensity or power or force.
7. (Physics, chemistry) Not having atomic weight greater than average.
8. Psychologically light; especially free from sadness or troubles.
9. Demanding little effort; not burdensome.
10. Designed for ease of movement or to carry little weight.
11. Not fatty; not rich or heavily seasoned.
12. Having little importance.
13. Of the military or industry; using (or being) relatively small or light arms or equipment.
14. Intended primarily as entertainment; not serious or profound.
15. (Of sleep) Easily disturbed; SYN. wakeful.
16. Less than the correct or legal or full amount often deliberately so; SYN. scant, short.
(1786-1839) English soldier, naval officer, and surveyor in Australia, born in Malaya. He was appointed surveyor-general of the new colony of South Australia in 1836 and departed ahead of the main party. He chose the site for Adelaide on the banks of the Torrens River and stood firm against the attempts of Governor Hindmarsh to have it moved to the coast. He also laid out the plan for the settlement's center and is regarded as the founder of Adelaide.
ETYM Old Eng. light, liht, as. leóht; akin to os. lioht, Dutch and German licht, Old High Germ. lioht, Goth. liuhath, Icel. ljôs, Latin lux light, lucere to shine, Greek leykos white, Skr. ruc to shine. Related to Lucid, Lunar, Luminous, Lynx.
1. Having abundant light or illumination: or; SYN. lighting.
2. Any device serving as a source of visible light; SYN. light source.
3. An illuminated area.
4. A visual warning signal.
5. A particular perspective or aspect of a situation.
6. A condition of spiritual awareness; divine illumination; SYN. illumination.
7. The visual effect of illumination on objects or scenes as created in pictures; SYN. lightness.
8. (Physics) Electromagnetic radiation that can produce a visual sensation; SYN. visible light, visible radiation.
9. Public awareness.
10. Mental understanding as an enlightening experience.
11. A person regarded very fondly.
Electromagnetic waves in the visible range, having a wavelength from about 400 nanometers in the extreme violet to about 770 nanometers in the extreme red. Light is considered to exhibit particle and wave properties, and the fundamental particle, or quantum, of light is called the photon. The speed of light (and of all electromagnetic radiation) in a vacuum is approximately 300,000 km/186,000 mi per second, and is a universal constant denoted by c.
Issac Newton was the first to discover, 1666, that sunlight is composed of a mixture of light of different colors in certain proportions and that it could be separated into its components by dispersion. Before his time it was supposed that dispersion of light produced color instead of separating already existing colors.
The ancients believed that light traveled at infinite speed; its speed was first measured accurately by Danish astronomer Ole Römer 1676.
Optics is a very ancient branch of physics. It is stated that a lens of rock crystal was found in the ruins of Nineveh, while Aristophanes mentions the use of burning-glasses in The Clouds. Reflection and refraction were known to the Greeks in 300 bc, and theories of vision were formulated by the Pythagoreans and the Platonists. Cleomedes, a Roman of the time of the Emperor Augustus, following Ptolemy, extended the knowledge of refraction and explained that atmospheric refraction enables us to see the Sun after it has set. Alhazen (about 10th century ad) wrote a book on optics, and, in addition to advancing the knowledge of reflection and refraction, made a close study of the optics of the human eye. Roger Bacon (13th century ad) made notable contributions and prophesies in optics, some of which bore fruit when Galileo constructed one of the first telescopes in 1609. Willebrord Snell of Leyden discovered the law of refraction about this time, and Newton explained it by the assumption of a corpuscular theory o
F light. According to this theory a luminous body emits swarms of corpuscles that travel in straight lines through the all-pervading ether. Christiaan Huygens, a contemporary of Newton, formulated a wave theory of light, but Newton’s great contributions to the knowledge of light, combined with his great reputation, caused his theory to be favored, and it was left to Augustine Fresnel (1788–1827) and Thomas Young (1773–1829) to establish Huygens’s theory by the evidence of their experiments on diffraction and interference.
The 19th century saw the development of the elastic solid theory of the ether, the medium through which light was supposed to be propagated, but this finally gave place to the electromagnetic wave theory following James Maxwell's theoretical researches supported by the accurate determinations of the velocity of light. The emission of light from self-luminous bodies is an atomic phenomenon that was given a satisfactory explanation by Max Planck, Niels Bohr, and others in terms of the quantum theory. Similarly the absorption of light, and in particular the emission of electrons from metallic surfaces illuminated by light (photoelectric effect), was explained by the quantum theory.
Certain properties of light, however, are explained only on the hypothesis that light is propagated as electromagnetic waves. Thus the quantum theory accounts for the photoelectric effect, while the electromagnetic wave theory accounts for the interference of light. The relation between these two theories can be approached in terms of Werner Heisenberg's uncertainty principle.
See also refraction; diffraction; interference.