Incandescent Lamp
Arc Lamp
Fluorescent Lamp
Mercury Vapour Lamp
Compact Fluorescent Lamp (CFL)
Halogen Lamp
Sodium vapour Lamp
Light Emitting Diode (LED)
Incandescent Lamp
Incandescent means producing visible light by heating an object. An incandescent lamp works on the same principle.
The electrical light source which works on the principle of incandescent phenomenon is called as incandescent lamp.
In other words, the lamp working due to glowing of the filament caused by electric current through it, is called as incandescent lamp.
Construction of Incandescent Lamp
- Filament:- Very thin wire, usually made of tungsten, emit light rays when current passes through it.
- Contact Wire :- Electric conductor carrying the current to the filament.
- Inert gas :- Gas inserted in the bulb to slow down the evaporation of filament.
- Support wire Support wire holds the filament.
- Bulb Gas inserted in glass envelope into which the body of lamp is inserted.
- Electrical foot contact Establish electrical connection between electrical main and lamp.
Working of Incandescent Lamp
When an object is made hot, the atoms inside the object become thermally excited.The outer orbit electrons of the atoms jump to higher energy level due to supplied energy.The electrons on these higher energy levels are not stable, they again fall back to lower energy levels.
While falling from higher to lower energy levels, the electrons release their extra energy in a form of photons. These photons are then emitted from the surface of object in the form of electromagnetic radiation. The electromagnetic wave with wavelengths within the range of infrared is heat energy and the electromagnetic wave with wavelengths within visible range is light energy.
Advantages of Incandescent Lamp
- Less cost. 2. Can be operated at normal voltage. 3. Good radiation characteristics. 4. Available in various shops. 5. Available everywhere easily.
Disadvantages of Incandescent Lamp
- Life is less as compared to other lamp. 2. Power consumption is more.
Arc Lamp
Arc lamp is a type of electric lamp which produces light by creating an ard arc in the place between two electrodes when electrical energy is supplied.
Construction of Arc Lamp
Working
In a arc lamp, the electrodes are connected together firstly. The electrodes are detached slowly. As a result of this, the electric current gets heated and the arc is maintained between the electrodes. The high intensity light is produced by this carbon vapour, which is highly Luminous in the arc.
Types of Arc Lamp
DC Carbon Arc Lamp
In this type of lamp, two electrodes placed touching to each other. DC supply of 40-60 volts is given. When current flows, rod soon becomes incandescent due to high resistance of carbon.
When they are slightly pulled so that the gap of 2-3 mm is formed, an arc is formed between the gap and light is produced. Transfer of carbon particles from one electrode to another maintain the arc. The burning rate of positive electrode is twice than burning rate of negative electrode.
AC carbon arc Lamp
Im AC carbon arc lamp the burning rate of both electrodes is same. It requires voltage of, V = 39+2.8l Where, l = length of arc in mm. Overall luminous efficiency of this lamp is low.
Application of Arc Lamp
Cinema projector, Search light
Fluorescent Lamp
When fluorescent material are subjected to electromagnetic radiation of particular wavelength, they get excited and in turns gives out radiation of some other lengths, and give out radiation even if the exciting radiation is removed.
Construction
Fluorescent tube consists of following parts :- 1
Tube :- Glass tube whifch is sealed with two filament at two ends. It is coated with fluorescent powder and Gilles with mercury and argon.
Choke :- Supply large potential for starting arc. Limits the arc current to safe value.
Starter:- Starter is provided to limit starting current.
Power factor improvement capacitor :- It is used for power factor improvement.
Working
When supply is ‘ON’ current flows through the choke – filament number 1 – starter – filament number 2 to neutral.
At that time choke induces high voltage which is applied to two filaments and ionized gas.
Due to this, there will be high voltage ionization so that light will be emitted through the tube.
Advantages of fluorescent tube
Efficiency is high about 90%, Life is more, Less glare.
Mercury Vapour Lamp
When mercury discharge under low pressure gives mainly ultra violet radiations. If pressure is increased to 1 or 2 atmosphere, it’s proportion of radiations in visible spectrum is increased and we get a light of bluish colour.
Construction of Mercury Vapour Lamp
Choke :- the choke is acting as the ballast. At the time of supply voltage variation, the current flowing through the inner tube is maintained constant to keep uniform light intensity.
Starting resistance / limiting resistance:- whenever current flows through the starting resistance, there is a I 2R loss occurs which is converted into heat. If the temperature of this heat goes near about 600°C then inert gasses ionization starts.
Auxiliary electrode and main electrode :- the ionization is takes place through the inert gasses whenever current flows from auxiliary electrode to main electrode.
Inner tube :- the various inert gasses eg.Argon , Nitrogen etc with Mercury powder are filled in the inner tube at 5 to 7 times of the atmospheric pressure.
Outer tube :- the function of outer tube is to make the vaccum surrounding in the inner tube to avoid thermal dissipation.
Power factor improvement capacitor:- the function of power factor improvement capacitor is to improve the power factor.
Working of Mercury Vapour Lamp
Whenever single phase, 230v, AC supply is provided to the discharge tube of MVL initially current flows from phase to choke to the starting electrode to neutral. The starting electrode or resistance is made up of tungsten filament having more resistance [5 to 10 KΩ], so that whenever current flows from tungsten filament, as per the thermal emission, the light is emitted through the filament.
At the same time the rated voltages is applied in between the main electrode no.2. Due to this voltage there will be collision of neon gas particles and current will start to flow through the discharge tube.Whenever temperature surrounding the inner tube increases up to 600°C the mercury powder will start vaporizing and the continuous collision process of all inert gasses takes place so that full light is emitted through the discharge tube.
Compact Fluorescent Lamp (CFL)
Construction
Screwbase and housing : it provides protection to electronic ballast.
Electronic Ballast : An electronic ballast is a device which controls the starting Voltage and the operating currents of the lighting devices.
Spiral Lamp : spiral lamp consist of argon and mercury and it is coated with triphosper coating.
Working of Compact Fluorescent Lamp
The electronic ballast circuit takes a 220 V input from external power source and sends high frequency supply is applied to that two terminals of CFL. This ionizes the argon and mercury vapor particles.
The ionized particles emit ultra violet radiations which strike with the fluorescent layer of material coated on the tube. High frequency AC Supply (60 80V at 1 KHz) is applied to the inert gases which are filled at low pressure. Then due to high frequency there will be ionization of mercury powder helium and other inert gases. And light is emitted through this fluorescent lamp.
Advantages of CFL
Low power consumption, Long life, Small size, Illumination is high.
Disadvantages of CFL
Initial cost is high.
Halogen Lamp
This is one type of incandescent lamp having number of advantages over the ordinary incandescent lamp. The life & efficiency of an incandescent lamp is affected by the gradual evaporation of tungsten and also its operating temperature but the addition of small amount of halogen vapour to the gas in bulb restores. In Halogen Lamp evaporated tungsten vapour back to the filament by means of chemical reaction and the cycle goes on this cycle is called as Halogen Cycle.
Construction of Halogen Lamp
Filament : Very thin wire, usually made of tungsten, emit light rays when current passes through it.
Haloengas : Prevents the evaporation of the tungsten filament.
Base : it holds the filament.
Lamp terminal Socket : Establish electrical connection between electrical mains and lamp.
Working of Halogen Lamp
A halogen lamp functions identically to an incandescent lamp, with one notable exception: The halogen cycle. The halogen gas reacts chemically with the evaporated tungsten to prevent it from affixing to the glass. Some tungsten is returned to the filament, which also serves to increase the rated life of the lamp.
Advantages of Halogen Lamp
Longer lifetime, Instant Startup, Compact size, No blakening of lamp, Higher lumen output
Disadvantages
Extremely hot
Applications of Halogen Lamp
Spot light, Film projectors, Scientific Instruments
Sodium vapour Lamp
Construction of Sodium vapour Lamp
Sodium vapour lamp consist of ‘u’ shaped tube and at the ends of the tube two electrodes are sealed. This tube is filled with sodium (solid sodium) and small quantity of neon gas. Since there is great effect of the change of surrounding temperature on the light output given by the lamp. Hence the inner tube is enclosed in an outer double walled gas tube.
Working of sodium vapour lamp
Before the lamp starts working, the sodium is usually in solid form deposited on the sides of wall in the inner tube. When the voltage is applied to the lamp, it warms up and starts vapourising slowly and radiates out yellow colour light.
After 10 to 20 minutes, the lamp starts giving it’s full output. For this a voltage is about 230v. Supply is given through a leakage transformer.
Advantages
Average life is about 2500 – 3000 hours, Luminous efficiency is 50 lume / watt, Low operating temperature, Effective in rainy and foggy season.
Disadvantages
Starting time required, It requires additional transformer, Poor power factor.
Applications
Street lightening, Lightening for open space, Highway lightening
Light Emitting Diode (LED)
A LED is a special type of P-N junction diode.
The LED is specially dopped and made of a special type of semiconductor
This diode can emit light when it is in forward biased state.