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light

 [līt]
electromagnetic radiation with a range of wavelength between 390 (violet) and 770 (red) nanometers, capable of stimulating the subjective sensation of sight; sometimes considered to include ultraviolet and infrared radiation as well.
idioretinal light (intrinsic light) the sensation of light in the complete absence of external stimuli.
polarized light light of which the vibrations are made over one plane or in circles or ellipses.
Wood's light ultraviolet radiation from a mercury vapor source, transmitted through a nickel-oxide filter (Wood's filter or glass), which holds back all but a few violet rays and passes ultraviolet rays of wavelength around 365 nm; used in diagnosis of fungal infections of the scalp and erythrasma, and to reveal the presence of porphyrins and fluorescent minerals.

light

(līt),
1. That portion of electromagnetic radiation (for example, 390-770 nm) to which the retina is sensitive (wavelength range, 380-780 nm).
See also: lamp.
See also: lamp.
2. Describing a solid element, having a low density.
See also: lamp.
3. Having a subnormal mass.
See also: lamp.
[A.S. leōht]

light

photophobia.

light

Electromagnetic radiation, usually understood to be in the range of visible light–ie, 390 to 770 nm. See Curing light, Ultraviolet light.

light

(līt)
That portion of electromagnetic radiation to which the retina is sensitive.
See also: lamp
[A.S. leōht]

light

that part of the ELECTROMAGNETIC SPECTRUM which is visible to the human eye between about 400 nm (blue) and 770 nm (red).

light

Electromagnetic vibration capable of stimulating the receptors of the retina and of producing a visual sensation. The radiations that give rise to the sensation of vision are comprised within the wavelength band 380-780 nm. This band is called the visible spectrum or visible light. The borders of this band are not precise but beyond these radiations the visual efficacy of any wavelength becomes very low indeed (less than 10−25). See coherent sources; infrared; absorptive lens; spectroscope; electromagnetic spectrum; visible spectrum; Table C4; quantum theory; wave theory; ultraviolet; wavelength.
achromatic light See achromatic light stimulus.
light adaptation See light adaptation.
artificial light Any light other than natural light.
beam of light A collection of pencils arising from an extended source or object. Syn. bundle of light. See pencil of light.
bundle of light See beam of light.
light chaos See idioretinal light.
cold light Any visible light emitted by a process other than incandescence such as lasers, glow worms, certain chemical reactions, etc. Cold light is free of infrared.
compound light Light composed of more than one wavelength.
diffuse light Light coming from an extended source and having no predominant directional component. Illumination is thus relatively uniform with a minimum of shadows. See diffusion; extended source.
fluorescent light Light emitted by fluorescence as in a fluorescent lamp. Electricity excites a gas that produces ultraviolet light, which in turn causes a phosphor coating on the inner surface of the fluorescent tube to fluoresce and emit visible light. Examples: mercury vapour lamp, neon and argon lamps, sodium vapour lamp, xenon flash lamp.
frequency of light See hertz; electromagnetic spectrum; wavelength.
idioretinal light A visual sensation occurring in total darkness that is attributed to spontaneous nervous impulses in the neurons of the visual pathway. Syn. intrinsic light; light chaos.
incandescent light Light emitted by incandescence as in an incandescent lamp. An electrical current passes through a thin filament (e.g. tungsten) enclosed in a sealed oxygen-free glass bulb. The filament is heated and photons are released. See filament lamp; halogen lamp.
infrared light See infrared.
intrinsic light See idioretinal light.
monochromatic light Light consisting of a single wavelength or, more usually, of a narrow band of wavelengths (a few nanometres).
natural light Light received from the sun and the sky.
pencil of light A narrow cone of light rays coming from a point source or from any one point on a broad source after passing through a limiting aperture. A pencil of light may be convergent, divergent or parallel. The ray passing through the centre of the aperture is the chief ray. Syn. homocentric bundle of rays; homocentric pencil of rays. See beam of light.
polarized light Ordinary light is composed of transverse wave motions uniform in all directions in a plane perpendicular to its direction of propagation. Polarized light is composed of transverse wave motions in only one direction, called the plane of vibration. Polarized light can be obtained by using a polarizer (e.g. tourmaline crystals, polarizing material such as Polaroid, Nicol prism, etc.). See analyser; angle of polarization; dichroic crystal; polarizing lens; polarizer; Wollaston prism; vectogram.
quantity of light Product of luminous flux and its duration. Unit: lumen-second. See lumen.
light reflex See corneal reflex; pupil light reflex.
solar light Light from the sun or having identical properties as the sun. See eclipse blindness; white light.
light source Any source of visible radiant energy such as natural light (e.g. daylight, moonlight, sunlight) or artificial light (e.g. a candle flame, an incandescent lamp, a discharge lamp, a fluorescent lamp). See coherent sources; CIE standard illuminants.
speed of light The currently accepted figure is 299 792.5 km/s (in a vacuum). This velocity decreases, differentially with wavelength, when the radiation enters a medium. See index of refraction; electromagnetic spectrum.
light stop See diaphragm.
stray light Light reflected or passing through an optical system but not involved in the formation of the image such as that reflected by the surfaces of a correcting lens. Syn. parasitic light. See ghost image.
light threshold See light absolute threshold.
ultraviolet light See ultraviolet; Wood's light.
visible light See light; visible spectrum.
white light Light perceived without any attribute of hue. Any light produced by a source having an equal energy spectrum will appear white after the eye is adapted. Some of the CIE illuminants are often used as a source of white light, e.g. B, C and D. Sunlight is a source of white light. See chromaticity diagram; equal energy spectrum.
Wood's light Ultraviolet light near the visible spectrum which, when used with certain dyes such as fluorescein, causes fluorescence. It is produced by a special type of glass (called Wood's glass or Wood's filter), which contains nickel oxide and transmits ultraviolet radiations near the visible spectrum. It is used to detect corneal abrasions and to evaluate the fit of hard contact lenses. It is available in a slit-lamp or in a Burton lamp. See fluorescein; fluorescence; Burton lamp.

light

(līt)
That portion of electromagnetic radiation to which the retina is sensitive.
See also: lamp
[A.S. leōht]
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