"The angle under which the rays of light, coming from the extremities of an object, cross each other at the eye, bears a proportion directly to the length, and inversely to the distance of the object." -Comstock 1850

Angle of Vision

"The angle under which the rays of light, coming from the extremities of an object, cross each other…

"The arc lamp is essentially a device for automatically separating the carbons when the current is turned on, for 'feeding' the carbons together as they are burned away at their tips, and, in some cases, for short-circuiting the lamp in case of irregularity or accident." -Avery 1895

Arc Lamp

"The arc lamp is essentially a device for automatically separating the carbons when the current is turned…

An arc lamp or arc light is the general term for a class of lamps that produce light by an electric arc (also called a voltaic arc). The lamp consists of two electrodes typically made of tungsten which are separated by a gas.

Arc Light

An arc lamp or arc light is the general term for a class of lamps that produce light by an electric…

"Beacons in exposed situations are constructed sometimes of stone, and cement-concrete or cement-rubble, but generally of castiron columns let into heavy base plates which are fixed to the rock by strong lewis bats. The small class iron beacons are generally of malleable iron and the larger of cast-iron butt steel or bronze might with advantage be used in very exposed places." —The Encyclopedia Britannica, 1910

Beacon

"Beacons in exposed situations are constructed sometimes of stone, and cement-concrete or cement-rubble,…

"An optical instrument employed for exhibiting the images of objects in their forms and colors, so that they may be traced and a picture drawn, or may be represented by photography. A simple camera obscura is presented by a darkened chamber into which no light is permitted to enter excepting by a small hole in the window-shutter. A picture of the objects opposite the hole will then be seen on the wall or on a white screen placed opposite the opening." — Winston's Encyclopedia, 1919

Camera Obscura

"An optical instrument employed for exhibiting the images of objects in their forms and colors, so that…

"Camera obscura strictly signifies a darkened chamber, because the room must be darkened, in order to observe its effects. To witness the phenomena of this instrument, let a room be closed in every direction, so as to exclude the light. Then from an aperture, say of an inch in diameter, admit a single beam of light, and the images of external things, such as trees and houses, and persons walking the streets, will be seen inverted on the wall opposite to where the light is admitted, or on a screen of white paper, placed before the aperture. The reason why the image is inverted will be obvious, when it is remembered that the rays proceeding from the extremities of the object must converge in order to pass through the small aperture; and as the rays of light always proceed in straight lines, they must cross each other at the point of admission. Thus the pencil a, coming from the upperpart of the tower, and proceeding straight, will represent the image of the part at b, while the lower part c, for the same reason, will be represented at d." —Comstock, 1850

Camera Obscura

"Camera obscura strictly signifies a darkened chamber, because the room must be darkened, in order to…

"Camera obscura strictly signifies a darkened chamber, because the room must be darkened, in order to observe its effects. To witness the phenomena of this instrument, let a room be closed in every direction, so as to exclude the light. Then from an aperture, say of an inch in diameter, admit a single beam of light, and the images of external things, such as trees and houses, and persons walking the streets, will be seen inverted on the wall opposite to where the light is admitted, or on a screen of white paper, placed before the aperture. The reason why the image is inverted will be obvious, when it is remembered that the rays proceeding from the extremities of the object must converge in order to pass through the small aperture; and as the rays of light always proceed in straight lines, they must cross each other at the point of admission. Thus the pencil a, coming from the upperpart of the tower, and proceeding straight, will represent the image of the part at b, while the lower part c, for the same reason, will be represented at d." —Comstock, 1850

Camera Obscura

"Camera obscura strictly signifies a darkened chamber, because the room must be darkened, in order to…

A cylinder of tallow, wax, spermaceti, paraffine, or other combustible substance, inclosing a wick, and used to furnish light.

Candle

A cylinder of tallow, wax, spermaceti, paraffine, or other combustible substance, inclosing a wick,…

A wax candle, lit..

Candle

A wax candle, lit..

A candle is a light source consisting of a solid block of wax and a wick. Pictured is a hand lighting the candle with a match.

Candle

A candle is a light source consisting of a solid block of wax and a wick. Pictured is a hand lighting…

"Catadioptric Fixed Light.—This apparatus, in which a central burner is used, consists of a dioptric cylindric refractor with zones of silvered mirror above and below similar in profile to Bordier Marcet's reflector. By the adoption of the refractor the whole of the wasteful divergence which occurs in Marcet's reflector is prevented. We have here a geometrically perfect combination, but it is not so physically, because metallic reflexion is used. This physical defect Fresnel obviated in his next design." —The Encyclopedia Britannica, 1910

Catadiopteric Light

"Catadioptric Fixed Light.—This apparatus, in which a central burner is used, consists of a dioptric…

"Catadioptric Fixed Light.—This apparatus, in which a central burner is used, consists of a dioptric cylindric refractor with zones of silvered mirror above and below similar in profile to Bordier Marcet's reflector. By the adoption of the refractor the whole of the wasteful divergence which occurs in Marcet's reflector is prevented. We have here a geometrically perfect combination, but it is not so physically, because metallic reflexion is used. This physical defect Fresnel obviated in his next design." —The Encyclopedia Britannica, 1910

Catadiopteric Light

"Catadioptric Fixed Light.—This apparatus, in which a central burner is used, consists of a dioptric…

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years it has been used in the harbour lights of Great Britain when in the neighborhood of gas-works. Mr. J. R. Wigham has designed a compound or crecus burner consisting of a group of twenty-eight vertical tubes, each carrying an ordinary double fish-tail burner, and the ignited gases issuing from all these jets unite into one large flame." —The Encyclopedia Britannica, 1910

Coal-gas

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years…

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years it has been used in the harbour lights of Great Britain when in the neighborhood of gas-works. Mr. J. R. Wigham has designed a compound or crecus burner consisting of a group of twenty-eight vertical tubes, each carrying an ordinary double fish-tail burner, and the ignited gases issuing from all these jets unite into one large flame." —The Encyclopedia Britannica, 1910

Coal-gas

"Coal-gas was first used as a lighthouse illuminant at Salvore, near Trieste, in 1817. For many years…

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing principle all the light can be distributed with strict equality over 112 degrees, which is the arc prescribed for steamers by the Board of Trade. Several of the Transatlantic and other steamers have adopted this kind of apparatus, which is hung on gimbals and placed in iron towers, having an entry from below the deck, which can be made use of in bad weather." —The Encyclopedia Britannica, 1910

Condensing Apparatus

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing…

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing principle all the light can be distributed with strict equality over 112 degrees, which is the arc prescribed for steamers by the Board of Trade. Several of the Transatlantic and other steamers have adopted this kind of apparatus, which is hung on gimbals and placed in iron towers, having an entry from below the deck, which can be made use of in bad weather." —The Encyclopedia Britannica, 1910

Condensing Apparatus

"Condensing Apparatus for Steamer's Side Lights.—By means of this application of the condensing…

"Fixed Conensing Light for a Single Sector, 1850.—The holophote Light pLp throws its whole light on straight condensing prisms c, each of which distributes the rays over the required sector." —The Encyclopedia Britannica, 1910

Condensing Light

"Fixed Conensing Light for a Single Sector, 1850.—The holophote Light pLp throws its whole light…

"Condensing Octant.—The central fixed apparatus bb with spherical mirror dd throws its rays directly over the angle of 45 degrees pgp, while the supplemental rays fall upon the straight condensing prisms p, each of which spreads the incident rays parallel to the corresponding rays in the central angle pgp. In this way the whole of the front hemisphere of rays is parallelized in the vertical plane and spread equally over the 45 degree in azimuth." —The Encyclopedia Britannica, 1910

Condensing Octant

"Condensing Octant.—The central fixed apparatus bb with spherical mirror dd throws its rays directly…

"Condensing Octant.—The central fixed apparatus bb with spherical mirror dd throws its rays directly over the angle of 45 degrees pgp, while the supplemental rays fall upon the straight condensing prisms p, each of which spreads the incident rays parallel to the corresponding rays in the central angle pgp. In this way the whole of the front hemisphere of rays is parallelized in the vertical plane and spread equally over the 45 degree in azimuth." —The Encyclopedia Britannica, 1910

Condensing Octant

"Condensing Octant.—The central fixed apparatus bb with spherical mirror dd throws its rays directly…

"Condensing Quadrant.—The fixed apparatus bbb, with spherical mirror behind, throws its rays directly through the angle of 90 degrees afa', while the supplementary rays falling on the straight condensing prisms p, p, p', p' are sent out parallel to the corresponding rays in the unobstructed central quadrant of the main apparatus. The whole light will therefore be condensed equally over 90 degrees." —The Encyclopedia Britannica, 1910

Condensing Quadrant

"Condensing Quadrant.—The fixed apparatus bbb, with spherical mirror behind, throws its rays directly…

"The refraction of water is beautifully proved by the following simple experiment. Place an empty cup, with a shilling on the bottom, in such a position that the side of the cup will just hide the piece of money from the eye. Then let another person fill the cup with water, keeping the eye in the same position as before. As the water is poured in, the shilling will be come visible, appearing to rise with the water. The effect of the water is to bend the ray of light coming from the shilling, so as to make it meet the eye below the point where it otherwise would. Thus the eye could not see the shilling in the direction of c, since the line, of vision is towards a, and c is hidden by the side of the cup. But the refraction of the water bends the way downwards, producing the same effect as though the object had been raised upwards, and hence it becomes visible." —Comstock, 1850

Cup and Shilling

"The refraction of water is beautifully proved by the following simple experiment. Place an empty cup,…

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the radius of curvature of the inner face of an annular lens. The outer face is the same as that of an ordinary annular lens, which the other face, though straight in the vertical, is ground to the required curve in the horizontal plane. The rays f'fc falling upon the lens x converge to the vertical focal plane ff and afterwards diverge through the smaller horizontal angle x'f'x', and so for any other case." —The Encyclopedia Britannica, 1910

Differential Lens

"Differential Lens.—Horizontal divergence may be obtained to any required amount by varying the…

"Throw a sunbeam through a very small opening in the shutter of a darkened room. Receive the beam upon a convex lens of short focal length, placing a pieve of red glass between the aperture and the lens. Place and opaque screen with a sharp edge beyond the focal distance of the lens, as at a, so as to cut off the lower part of the cone of homogeneous light, and project the upper part thereof upon a screen at b." -Avery 1895

Diffraction

"Throw a sunbeam through a very small opening in the shutter of a darkened room. Receive the beam upon…

A diagram of action of diffraction grating.

Diffraction grating

A diagram of action of diffraction grating.

"Since A is producing light and larger than object B, the shadow of B continuously shrinks to a single point at C." —Quackenbos 1859

Diminish Shadow

"Since A is producing light and larger than object B, the shadow of B continuously shrinks to a single…

"First Application of Total Reflexion to Fixed Lights. In this apparatus Fresnel substituted his totally reflecting prism p and lens R for Marcet's reflector, and thus distributed the whole light equally over the horizon by means of dioptric agents alone. This was the first application of total reflexion to lighthouse apparatus, and this beautiful instrument continues till now in universal use." —The Encyclopedia Britannica, 1910

Dioptric Light

"First Application of Total Reflexion to Fixed Lights. In this apparatus Fresnel substituted his totally…

"Dioptric Floating Light. Elevation." —The Encyclopedia Britannica, 1910

Dioptric Light

"Dioptric Floating Light. Elevation." —The Encyclopedia Britannica, 1910

"Dioptric Floating Light. Horizontal Section." —The Encyclopedia Britannica, 1910

Dioptric Light

"Dioptric Floating Light. Horizontal Section." —The Encyclopedia Britannica, 1910

"Section of Eddystone Light-house." — Chambers' Encyclopedia, 1875

Eddystone Light-house

"Section of Eddystone Light-house." — Chambers' Encyclopedia, 1875

An illustration of an elderly man with a lantern.

Elderly Man with Lantern

An illustration of an elderly man with a lantern.

A light fixture or luminaire is an electrical device used to create artificial light.

Lighting Fixture

A light fixture or luminaire is an electrical device used to create artificial light.

"aa is the mast, b tackle hook, c, c brass flanges for fixing parts of lantern together, e and g weather guards, h plate glass front of lantern, i shutter by which lamps are trimmed, k lamps, l silver reflector. Revolving catoptric apparatus was applied to floating lights in England, and M. Letourneau, in 1851, proposed to employ a number of sets of dioptric apparatus in one lantern." —The Encyclopedia Britannica, 1910

Floating Lights

"aa is the mast, b tackle hook, c, c brass flanges for fixing parts of lantern together, e and g weather…

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded by annular lenses L, and a compound arrangement of inclined trapezoidal lenses L' and plane silvered mirrors M. The inclined lenses fit closely to each other and form a pyramidal dome, and the light, intercepted by them, is sent upwards in inclined beams until, falling upon the plane mirrors M, it is sent outwards in horizontal parallelized beams. All these optical agents are made to revolve round the central lamp, and the sailor receives a full flash when the axis of one of the emerging beams passes his eye, and as soon as it passes him he is in darkness until the next beam comes round." —The Encyclopedia Britannica, 1910

Fresnels Revolving Light

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded…

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded by annular lenses L, and a compound arrangement of inclined trapezoidal lenses L' and plane silvered mirrors M. The inclined lenses fit closely to each other and form a pyramidal dome, and the light, intercepted by them, is sent upwards in inclined beams until, falling upon the plane mirrors M, it is sent outwards in horizontal parallelized beams. All these optical agents are made to revolve round the central lamp, and the sailor receives a full flash when the axis of one of the emerging beams passes his eye, and as soon as it passes him he is in darkness until the next beam comes round." —The Encyclopedia Britannica, 1910

Fresnels Revolving Light

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded…

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded by annular lenses L, and a compound arrangement of inclined trapezoidal lenses L' and plane silvered mirrors M. The inclined lenses fit closely to each other and form a pyramidal dome, and the light, intercepted by them, is sent upwards in inclined beams until, falling upon the plane mirrors M, it is sent outwards in horizontal parallelized beams. All these optical agents are made to revolve round the central lamp, and the sailor receives a full flash when the axis of one of the emerging beams passes his eye, and as soon as it passes him he is in darkness until the next beam comes round." —The Encyclopedia Britannica, 1910

Fresnels Revolving Light

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded…

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded by annular lenses L, and a compound arrangement of inclined trapezoidal lenses L' and plane silvered mirrors M. The inclined lenses fit closely to each other and form a pyramidal dome, and the light, intercepted by them, is sent upwards in inclined beams until, falling upon the plane mirrors M, it is sent outwards in horizontal parallelized beams. All these optical agents are made to revolve round the central lamp, and the sailor receives a full flash when the axis of one of the emerging beams passes his eye, and as soon as it passes him he is in darkness until the next beam comes round." —The Encyclopedia Britannica, 1910

Fresnels Revolving Light

"Fresnel's Revolving Light. —In this form of revolving light the central burner is surrounded…

"Electric gas lighting is often effected by sparks from the interrupted circuit of a voltaic battery, in which circuit is a 'kicking coil,' or by sparks from the secondary of an induction coil, or from a machine for the generation of static electricity." — Avery, 1895

Electric gas light

"Electric gas lighting is often effected by sparks from the interrupted circuit of a voltaic battery,…

A girl with a book, staring at a lit candle.

Girl and candle

A girl with a book, staring at a lit candle.

An illustration of a young girl lighting a candle on a table.

Girl Lighting a Candle

An illustration of a young girl lighting a candle on a table.

A magnifying glass.

Magnifying glass

A magnifying glass.

A hand holding a candlestick.

Hand with candle

A hand holding a candlestick.

"Holophotal Catadioptric Apparatus Revolving round a Central Flame.—If in place of Fresnel's compound arrangement of trapezoidal lenses and plane mirrors there are substituted mirrors R, R generated by the revolution of a parabolic profile round a horizontal axis, all the light will be at once sent out in parallel beams by them and the lenses L, and the apparatus is therefore geometrically perfect, but metallic instead of glass agents are still employed." —The Encyclopedia Britannica, 1910

Holophotal Catadioptric

"Holophotal Catadioptric Apparatus Revolving round a Central Flame.—If in place of Fresnel's compound…

"Holophotal Fixed Light varied by Flashes.—Fresnel's double agents are here also dispensed with by the single agency of panels of fixed light apparatus p', p' and cylindrical refractors L', L', alternating with panels of holophotal apparatus p, p, L, L, both of which revolve together round the central burner." —The Encyclopedia Britannica, 1910

Holophotal Light

"Holophotal Fixed Light varied by Flashes.—Fresnel's double agents are here also dispensed with…

"Slit A is a very small opening. The light coming from the soldier on the right shines through the slit in straight lines making the image of the soldier inverted on wall W." —Quackenbos 1859

Inverted Image

"Slit A is a very small opening. The light coming from the soldier on the right shines through the slit…

A small lamp with an open flame.

Lamp

A small lamp with an open flame.

A tall, slender lamp.

Lamp

A tall, slender lamp.

This lamp body is used for a lighting fixture; an electrical device used to create artificial light. A luminaries is a lighting fixture complete with the light source or lamp.

Lamp Body

This lamp body is used for a lighting fixture; an electrical device used to create artificial light.…

"Argand got his first suggestion for his burner-- invented in 1780-- from this style of alcohol lamp, then in general use throughout France." -Bodmer, 1917

Alcohol Lamp

"Argand got his first suggestion for his burner-- invented in 1780-- from this style of alcohol lamp,…

An illustration of an arc electric lamp or an arc lamp which produces light by an electric arc.

Arc Electric Lamp

An illustration of an arc electric lamp or an arc lamp which produces light by an electric arc.

A headlamp is attached to the front of a bicycle while illuminating the road ahead specially when there is low visibility.

Bicycle Lamp

A headlamp is attached to the front of a bicycle while illuminating the road ahead specially when there…

A lantern is a portable lighting device used to illuminate broad areas. Lanterns may be used for signaling, or as general light sources for camping also to guide your path somewhere. In the older days it would have been used like a torch. Dim varieties are often used for decoration.

Cycle Lamp

A lantern is a portable lighting device used to illuminate broad areas. Lanterns may be used for signaling,…

An arc lamp or arc light is the general term for a class of lamps that produce light by an electric arc. The lamp consists of two electrodes, typically made of tungsten, which are separated by a gas.

Electric Arc Lamp

An arc lamp or arc light is the general term for a class of lamps that produce light by an electric…

The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric light that works by incandescence, (a general term for heat-driven light emissions which includes the simple case of black body radiation).

Incandescent Lamp

The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric light…

A lamp is a replaceable component such as an incandescent light bulb, which is designed to produce light from electricity. These components usually have a base of ceramic, metal, glass or plastic, which makes an electrical connection in the socket of a light fixture.

Device for Conducting Electricity Into Lamps

A lamp is a replaceable component such as an incandescent light bulb, which is designed to produce light…

The incandescent light bulb, is a source of electric light that works by incandescence which is a general term for heat driven light emissions, which includes the simple cases of black body radiation.

Process of Producing Incandescing Bodies for Electric Lamps

The incandescent light bulb, is a source of electric light that works by incandescence which is a general…

A lampshade is a fixture that covers the light bulb on a lamp to diffuse the light it emits. Conical, cylindrical and other forms on floor-, desk- or table top-mounted as well as suspended lamp models are the most common and are made in a wide range of materials.

Incandescent Lampshade

A lampshade is a fixture that covers the light bulb on a lamp to diffuse the light it emits. Conical,…

"Two-light lancet." —D'Anvers, 1895

Two-light lancet

"Two-light lancet." —D'Anvers, 1895

A parabolic reflection lantern.

Lantern

A parabolic reflection lantern.