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Lamp is artificial source of light that will provide us light and will be operated with the electricity. Electrical lamp is basically energy convertor which will convert electrical energy in to light. The output of the lamp is steady means it will provide us radiant light also the lamp is not very expensive. The first lamp was invented by Thomas Edison in his own laboratory in New Jersey in 1879 January. It was glass bulb in which he fill vacuum and two carbon rods were used as a filament. Lamp can be used for various purposes such as indoor or outdoor. There are different types of application of lamp in which we used lamps such as indoor lightning, advertising, street light and for decoration. There are various types of lamps which are:
Fluorescent lamp is type of low pressure mercury vapour lamp which produces the visible light using fluorescent. Fluorescent lamp manufactured different variety of length and colour. But the working principles of all the fluorescent lamps are same.
Fluorescent Lam Construction:
Electrodes are fixed on both sides of the glass tube and the tip of electrodes is in spiral form which is generally made up of tungsten material. The coil is coated with electron emitting material. The tube is made up of lime glass which insulates heat. Inside the tube is coated with the fluorescent powder. The tube contains low pressure mercury vapour and argon. The circuit of the fluorescent lamp is connected with the switch and choke. The choke limits the high current and the starter allows equal amount of current on both sides of the electrodes. A capacitor is connected parallel to the starter which will improve the power factor in the circuit.
Working of fluorescent lamp:
When the circuit is connected with the supply the current will from the choke to the starter and the starter will allow the current on both sides of the electrodes. Since the resistance of the electrodes are high and when the current flow through it its temperature will start increasing. When the electrode heated temperature increases in the tube. Due to high temperature the mercury vapour and argon gas will be ionized. When medium between both electrodes are ionized then the current will start flowing in it and looks as arc.
The electrons along the arc will release energy in form electromagnetic radiation as the entire side the tube is coated with fluorescent powder which will increase the wavelength of electromagnetic radiation and will produce visible light. The efficiency of fluorescent lamp is higher as compared to incandescent lamp.
Incandescent lamp is a type of lamp which will provide the visible light by heating of filament through electric current. Incandescent lamp is round in shape. Incandescent is phenomenon in which object provide visible light due to heating.
Construction of the incandescent lamp:
The main element of the Incandescent lamp is filament which is connected between the two leads. The leads are connected with the supporting glass. The filament is made up of tungsten material and it contains two support wires that will provide support to the filament. The support wire is made up of molybdenum.
The outer envelope of the lamp is made up of glass and the bulb is fully closed and contains no air. Bulb will contain 85% argon and 15% Nitrogen. Both gases will be present inside the bulb. The inert gas argon will protect the filament to oxidize and will increase the life of the bulb. The filament can be designed in two ways:
- Coil filament
- Coiled coil filament
To produce large amount of light we will increase the size of filament. When we increase the size of filament in limited area we will use coiled coil filament. The lower portion of the bulb contains cap where the positive and negative terminals are located.
Working of Incandescent lamp:
When the lamp is connected with the supply the current will flow across the filament as the resistance of the filament is high due to which its temperature will increases. When the filament will be highly heated it will glow in case of the tungsten filament the resistivity is 5.6 ohm and its melting point is 3400° C. Due to which the filament will not melt at high temperature. When the filament is highly heated and glow the electrons will be release in form of photons. These photons emit light in form of electromagnetic radiation. In this way the Incandescent lamp provide us light.
There are different shapes, size and rating of incandescent lamp such as 25 W, 40W, 60W, 75W, 100W and 200W etc. Different materials are used as filament in Incandescent lamp such as:
- Tungsten which has melting point 3400° C
- Carbon which has melting point 3550° C
- Tantalum which has melting point 3017° C
These lamps are cheap and easy to use.
Incandescent lamps are divided in to the following types:
Carbon filament lamp:
The carbon filament lamp has the following features:
- Carbon element
- Operating temperature 1800° C to 2000° C
- Melting temperature 3500° C
- Less efficiency due to the negative temperature coefficient
- Operating time 600 to 800 hours
- 5 to 4 Lumens / watt
- It can be used in battery charging
Gas discharge lamp:
In these lamps gas discharge occurs and it is divided in to two types:
- High pressure lamp
- Low pressure lamp
The high pressure lamp is further divided in to two types:
- High pressure sodium vapour lamp
- High pressure mercury vapour lamp
The low pressure lamp is further divided in to two types:
- Low pressure sodium vapour lamp
- Low pressure mercury vapour lamp
Sodium vapour lamp:
Sodium vapour lamp is an electric discharge lamp which produce orange colour using sodium particles and inert gases neon and argon gas.
In glass tube metal electrodes are fixed when the arc will be produce inside the tube to increase the length of the arc the tube is designed u-shaped. The tube is made up of borosilicate glass.
The borosilicate glass does not damage on high temperature. The tube contains sodium, neon and argon gas. The outer envelope of the lamp is made up of glass. The inner side of the outer glass contain indium oxide coating which will reflect heat. The space between inner tube and outer tube contains vacuum. The metal is connected with the high reactance transformer and capacitor.
Working of Sodium vapour lamp:
The 40W Sodium vapour lamp require 380V to operate and 100W Sodium vapour lamp require 450V to operate. When we connect the sodium lamp with the supply the high reactance transformer will increase the voltage. When the electrode will get the require voltage arc will be formed. As there is neon and argon gas present in the tube so in starting the lamp will produce reddish pink colour and the temperature will increase in the tube. Sodium is present in metallic state which will vaporize due to high temperature. After 10 to 15 minutes when the sodium is completely converted in to vapours the lamp will produce orange colour light. The efficiency of the Sodium vapour lamp is 40 to 50 lumens / watt. The Sodium vapour lamp is available in 60 W, 85 W, 140 W.
There are several conditions in which Sodium vapour lamp will not produce light.
- When the metal electrode is brake or damage
- When sodium particles concentrate at one side of the inner tube
Sodium vapour lamp can be used in:
- High ways
- Street light
Sodium vapour lamp do not affect due to voltage variation
Mercury vapour lamp:
It is the type of lamp in which vaporized mercury is used and with the help electric arc produces the visible light is known as mercury vapour lamp. Mercury vapour lamp is gas discharge lamp. The efficiency of the Mercury vapour lamp is greater than incandescent lamp. The life of the Mercury vapour lamp is about 24000 hours.
Construction of Mercury vapour lamp:
The inner tube of the Mercury vapour lamp is made by quartz material. The outer layer is made up of borosilicate glass. The quartz and borosilicate are both heat insulting material. The main function of it is that when the heat will increase due to the arc so that the inner tube and envelop will not damage. The inner tube of the quartz can sustain 1300 K temperature. The outer envelope can sustain 700 kelvin temperature. Between the inner and outer tube contain nitrogen gas which will provide thermal insulation and protect the metal parts from oxidation. Mercury and argon are present inside the inner tube. The inner tube contains main and starting electrode. Both the electrodes are connected with the tungsten coil. Electrode is coated with the electron emitting material like thorium, calcium and barium carbonate. So that arc will be easily develop between both electrodes which will be connected with the molybdenum foil lead. A resistor is connected with starting electrode. When the current will flow across the starting electrode it will limit that current.
Working of Mercury vapour lamp:
When Mercury vapour lamp is connected with supply then the current will start flowing across the starting electrode and main electrode. There will be less gap between the main electrode and starting electrode. Due to a small gap voltage gradient remains high due to which a small arc will be generated between both electrodes. The current will be in limit by the resistor in the electrode. Due to this arc heat will be generated inside the tube. Mercury gas vaporized due to heat and also heat will be generated at the main electrode due to voltage. The heat generated will ionize the vaporized mercury. Thus main arc develop between both electrodes. Small arc will be stop after forming the main arc. After increasing the resistance of the starting resistor after 5 to 7 minutes mercury gas completely vaporized. The electrons across the arc produce the visible light in the form of electromagnetic radiation. Mercury vapour lamp produces light green and yellow colour of light.
There are two types of mercury vapour lamp:
- High pressure mercury lamp
In which pressure of mercury is high.
- Low pressure mercury lamp
In low pressure mercury vapour lamp pressure of mercury is low compared to high pressure mercury vapour.
Halogen lamps are the variation of the incandescent lamps technology. These lamps works by passing electricity through a tungsten filament which is enclosed in a tube containing halogen gas. This halogen gases chemical reaction to takes place which remove the tungsten from the walls of the glass and deposit back on the filament. This extends the light of the bulb in order for the chemical reaction to take place the filament needs to be hotter than what is needed for incandescent bulbs. The hotter filament produce a brilliant white light and is more efficient, more luminous per watt.
Compact fluorescent lamp:
Compact fluorescent lamp is modern type of light lamps that works like fluorescent lamps but in much smaller package. Similar to regular fluorescent lamps they produce little heat and are very efficient. They are available to fit screw type base fitting and pin type snap in. In most compact fluorescent lamp is either consists of a number of short glass sticks or two or three small tubular loops. Sometimes they are enclosed in glass bowl made to look similar to a regular incandescent lamp. Most compact fluorescent lamp cannot be used with dimmers. They normally last up to 10000 hours.
Light emitting diodes lamp are without a filament and are low power consumption and have a long life span. LED are just start to rival conventional lightning but unfortunately they just do not have output lumen needed to completely replace incandescent and other type bulbs just yet nevertheless technology is advancing every day and it will not be long the LED bulb will be the bulb of choice for the most application in the home and workplace.
Carbon arc lamp:
The carbon arc lamp is made up of glass which consists of two carbon rods. When these two rods touch each other by supplying electricity and it will provide arc which gives us light continuously until the electric current flow in it. The spacing between the rods must be proper so that if it is very narrow a very less light will be produce through it and if the spacing is large the light will flicker.