INCANDENSCENT LAMP

Incandescent LampsAn incandescent light bulb, incandescent lamp or incandescent light globe is an electric light which produces light with a filament wire heated to a high temperature by an electric current passing through it, until it glows . The hot filament is protected from oxidation with a glass or quartz bulb that is filled with inert gas.

CONSTRUCTION OF INCANDENSCENT LAMP

It consists of tungsten filament enclosed in air tight glass chamber.

Chemically inert gas is filled in the bulb to prevent oxidation and lowering of filament temperature.

Usually nitrogen or argon gas is used and sometimes a mixture of 85% of argon and 15% of nitrogen is also used.

Follwing are the parts of incandenscent lamp:

Filament It is in coil form in order to reduce the heat loss and to increase efficiency .

Support wires are used for supporting the filament and are made up of molybdenum wires .

Base :-To fix the lamp in holder. It is made up of alluminium wire.

Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, and work equally well on either alternating current or direct current. As a result, the incandescent lamp is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.

In addressing the question of who invented the incandescent lamp, historians Robert Friedel and Paul Israel list 22 inventors of incandescent lamps prior to Joseph Swan and Thomas Edison. They conclude that Edison's version was able to outstrip the others because of a combination of three factors: an effective incandescent material, a higher vacuum than others were able to achieve and a high resistance that made power distribution from a centralized source economically viable.

Gas filled lampsDifferent colours of light when different gases are used.

Halogen LampsA halogen lamp, also known as a tungsten halogen, quartz-halogen or quartz iodine lamp, is an incandescent lamp that has a small amount of a halogen such as iodine or bromine added. The combination of the halogen gas and the tungsten filament produces a halogen cycle chemical reaction which redeposits evaporated tungsten back onto the filament, increasing its life and maintaining the clarity of the envelope. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life, producing light of a higher luminous efficacy and color temperature. The small size of halogen lamps permits their use in compact optical systems for projectors and illumination.

Advantages of Halogen Lamps

Their life is almost double that of conventional tungsten lamp.

Almost no blackening.Hence a high lumen output is maintained throughout the life of the lamp.

Better colour

Reduced Dimensions

Halogen lamps are very suitable for outdoor illlumination of buildings, play grounds, car parks, airport runways etc.They are available upto 5kW.

Fluorescent lamps

Mercury vapour lamps A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube.

Advantages of Mercury vapour lamps

Mercury vapour lamps are more energy efficient than incandescent and most fluorescent lights, with luminous efficiencies of 35 to 65 lumens/watt.Long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output. For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights. They offer better color rendition than the more efficient high or low-pressure sodium vapor lamps.

Ametal-halide lamp (similar to HPMV lamp)is an electriclampthat produceslightby an electric arc through a gaseous mixture of vaporized mercury andmetal halides(compounds ofmetalswith bromine or iodine). It is a type of high-intensity discharge (HID) gas dischargelamp. It improve the efficacy and color renditionof the light.

it provides most of its light from the electric arc within a small discharge tube.

Mercury lamps

Sodium vapour lampsSodium vapour lamps have replaced mercury lamps due to their high lumen output for the same power input. The efficiency of sodium vapour lamps is between 40 to 50 lumens per watt with an average life of about 3000 hours. It is not affected by voltage variations. The glass tube is made specially chemical resistant to withstand the chemical reaction of hot sodium. The lamp must be operated at horizontal or nearly horizontal position to keep the sodium uniform throughout.

Sodium vapour lamps

Neon tube

Fluorescent Tubes\LampsThe tubes filled with argon gas at low pressure and one or two drops of mercury. The inner surface of the tube has a thin coating of fluorescent material. Different colours can be obtained depending upon the type of coating material used. It is provided with two electrodes coated with electron emissive material. The mercury vapour emits UV radiation when electric charge is passed through it. The fluorescent coating curves UV radiation into visible light.

Compact Fluorescent lamp

Compact fluorescent lampA compact fluorescent lamp(CFL) is a type of fluorescent lamp.Compared to other incandescent lamps CFLs use less power to give same amount of visible light.They have longer rated life, but generally have o high purchase price. Like all other fluorescent lamps , CFLs contain mercury , this complicates the disposal of fluorescent lamps.

Construction of CFLsThere are two main parts in CFLs:1)The gas filled tube and2)The magnetic or electronic ballast.Electronic ballasts contain a small circuit board with rectifiers , a filter capacitor and usually two switching transistors connected as high frequency resonant series DC to AC converter.The resulting high frequency is then applied to the lamp.

WORKINGElectrical energy in the form of an electrical current from the ballast flows through the gas , causing it to emit ultraviolet light.The ultraviolet light then excites the white phosphor coating on the tube .The coating emits visible light . CFLs then flickr when they have magnetic ballasts.

Advantages They have life span of about 6000 to 15000 hours.They are power saving lamps.

LED LAMP LED lamp is a type of solid state lighting that utilizes light emitting diodes as a source of illumination .

LED lamps are usually cluster of LEDs in a suitable housing.

They come in different shapes.

LEDs of different colourTHEY ARE HIGHLY EFFICIENT

ADVANTAGES OF LEDHIGH EFFICIENCYLEDs are now available that reliably offer over 100 lumen from a one watt device .

SMALL SIZEThey provides design facility , can be arranged in rows, rings and clustres.

HIGH DURABILITYThey have no filament or tube to break.

APPLICATIONSTRAFFIC LIGHTSSTAGE LIGHTNINGELECTRIC TORCHES BILLBOARD DISPLAYSTRAIN LIGHTSDOMESTIC LIGHTNINGFLOODLIGHTNING OF BUILDINGS

ActivityIllumination Foot-candlesOffices: Average Reading and Writing50-75Offices: Hallways10-20Offices: Rooms with Computers20-50Auditoriums / Assembly Places15-30Hospitals: General Areas10-15Labs / Treatment areas50-100Libraries30-100Schools30-150

****