Sonepat Slide: 3 Light, is a part of radiant energy which means that light is radiated from a point or object. Some bodies are luminous means they emit light by themselves e.g. stars, candle flame, hot filament etc. Non-luminous bodies do not emit light. They can be seen when light falls on them e.g. book, you, me etc.
Sonepat Slide: 4 All substances on the earth can be divided into three categories. Transparent: Which allow light to pass through themselves. Opaque: Which do not allow light to pass through themselves. Translucent: Which allow only a part of the light to pass through themselves.
Sonepat Slide: 6 1879: Thomas Alva Edison created incandescentlighting the first practical light source. 1939: The first fluorescent bulb was introduced at the world’s fair in New York. 1950: Tungsten halogen lamps came into market. 2000: Research on LED’s as a source of light.
Sonepat Slide: 9 The velocity (speed in a particular direction) of light for all practical purposes is 3×108m/s. Light travels in waves. Waves have frequency. Frequency means number of cycles/sec. Its unit is Hz (Hertz). Wavelength is measured in metre.
Sonepat Slide: 13 When we sprinkle a small quantity of common salt on a flame, it emits yellow light. If copper sulphate is sprinkled on flame, the dominant colour becomes blue-green. That is how we can see variety of colours in fire works.
Sonepat Slide: 16 Lumen is a Latin word for light. Lumen means the total light energy radiated out from the source. It is like the amount of water spraying from a shower head. It is the Standard International unit of measure of the luminous flux of light.
Sonepat Slide: 17 LUX is the measurement of the light intensity falling on a surface. One LUX is equal to 1 lumen/m2. For calculating LUX, we have to know the room dimension, height of the lamp, reflections from the sides etc. These parameters are usually processed in a computer.
Sonepat Slide: 18 The surface temperature of the sun is around 6100K. The illumination from the sun on the earth’s surface can even exceed 100,000 LUX during a summer day at the equator. At night, the reflected light from the moon might be as high as 0.2 LUX.
Sonepat Slide: 20 Colour Temperature (K): The colour temperature of a lamp is a measure of the "warmth" or "coldness" of the light that it produces. Lamps that produce a "warm" or "yellowish" light have a low colour temperature. Lamps producing a pure white or bluish tinged light have a higher colour temperature.
Sonepat Slide: 21 Lamps with a colour temperature of less than 3500K are usually described as having a "warm" appearance. Lamps with a colour temperature between 3500 and 5000K are considered to have a "cool" appearance, Lamps having a colour temperature over 5000K are said to have a "cold" appearance.
Sonepat Slide: 24 Cathode & Anode: Cathode: Any substance which is capable of releasing or giving out electrons is called cathode. Anode: Any substance which is ready and able to receive electrons is known as anode.
Sonepat Slide: 25 The electrons may be emitted from a cathode by any one of the following methods. 1. Thermionic emission (Heating). 2. Field emission (Magnetic or electrostatic) 3. Secondary emission (Striking) & 4. Photo emission (Light). 5. Radio active material.
Sonepat Slide: 26 In the thermionic emission, the cathode is required to be heated up to 3000K for the emission of electrons. However, thoriated tungsten may release electrons at about 2000K. But neither of the temperature is possible in a glass tube as glass starts softening at around 1000K.
Sonepat Slide: 27 Tungsten is the most preferred metal for making the filaments for the lamp. The main reasons for using tungsten for the filament are; 1. High melting point i.e. 3500K 2. Ductile; can be drawn into wires 3. Reasonable cost 4. Less evapouration.
Sonepat Slide: 28 Like other metals, tungsten also has 2 types of resistance namely cold & hot resistance The ratio between cold & hot is around 1:14. The RCOLD of a 60W incandescent lamp at 25°C is 62.32Ω. When connected across 230V, it drew 0.26A. Therefore, according to Ohm’s law; RHOT = 884.6 Ω
Sonepat Slide: 30 Emitter paste: It serves 3 purposes. 1. It increases the life of filament. 2. It reduces the ignition voltage required to start the discharge i.e. 1000V. 3. Tungsten filament emits electrons at higher temperature but due to emitter paste emission starts at 980K.
Sonepat Slide: 31 What is end blackening? Becoming ends of a fluorescent tube black! Emitter paste is the combination of the carbonates of calcium, barium & strontium. They have very good emissive characteristics. The emitter paste when heated gets evapourated and settles on the glass tube.
Sonepat Slide: 32 Generally, soda lime silica type glass is used for making electric lamp. This contains; 1. Silicon oxide 72% 2. Calcium oxide 7% 3. Sodium oxide 16% 4. Aluminium oxide 1% 5. Magnesium oxide 4% Calcium & Magnesium oxides together is also known as Dolomite.
Sonepat Slide: 33 Lead glass contains 20-30% of lead. This type of glass is preferred for making flare and exhaust tube. Why? 1. Lead is soft & malleable. 2. It is having lubricating property. 3. Low melting point. 4. High electrical insulating property.
Sonepat Slide: 34 Lead-in-wire: The function of lead-in-wire in electric lamp is to provide an electrical connection to the filament along with a glass to metal seal component. It has 3 parts namely inner, press/seal and outer lead. Inner Dumet Outer
Sonepat Slide: 35 The inner lead is to support the filament and is made of pure Nickel. The outer lead is directly connected to the power supply and is made of Monel metal which is an alloy of Ni & Cu. The press/seal section is made of an alloy known as DUMET. It is an alloy of Ni, C, Mn, Si, S, P & Fe.
Sonepat Slide: 36 In some countries, the lead-in-wire is made up of 4 sections. The 4th part acts as fuse wire and is made of either lead or tin. In case of any short circuit, fuse wire melts and power is disconnected. This saves energy and eliminates the fire risk.
Sonepat Slide: 37 Fluorescence: It is a property of absorbing ultraviolet radiation then emitting visible light. Also, it can be said that it is the physical process of slow emission of longer wavelength light by the absorption of shorter wavelength radiation.
Sonepat Slide: 39 Fluorescence suspension (mixture in which fine particles are suspended in a fluid where they are supported by buoyancy) contains: 1.Fluorescence powder 2.De-ionised/distilled water 3.Binder 4.Permanent re-inforcing agent 5.Surfactants 6.pH value conditioner
Sonepat Slide: 40 Surfactants stands for SURFace ACTive AgeNT means Molecule that lowers the surface tension. Surface tension: Forces on the surface of the liquid droplets that keep them from spreading out over treated surfaces. What happens when a drop of mercury falls on the floor?
Sonepat Slide: 41 Viscosity: Viscosity means thickness or resistance to flow of a liquid that generally decreases as temperature increases. Materials with a high viscosity do not flow readily. Example. Make a hole in the bottom of a cup, pour the honey. Cup drains very slowly. Fill the same cup with water. What happens?
Sonepat Slide: 43 pH value: Power of Hydrogen A convenient method of expressing small differences in the acidity or alkalinity of solutions. Lower value indicates increasing acidity. Higher value indicates increasing alkalinity. Neutral = 7.1 Pure water = 7 Human blood = 7.35
Sonepat Slide: 47 The job of a electric lamp is to convert electrical power (watt) into light (lumens). A higher lumen rating always means brighter lamp but a higher watt rating does not mean so. Efficiency of a electric lamp is measured in lumens/watt.
Sonepat Slide: 48 Production of Light: The difference method of producing light by electricity may, in abroad sense, be divided into three groups; By temperature incandescence. By establishing arc between electrodes. Discharge lamps. (i) Using fluorescence properties (ii) Not using fluorescence properties.
Sonepat Slide: 49 Temperature incandescence: A black body when heated to 6500K, emits the maximum energy in the visible spectrum of light. In this method, an electric current is passed through a filament of thin wire placed in vacuum or an inert gas. The current generates enough heat to raise the temperature of the filament to luminosity.
Sonepat Slide: 50 The output depends upon the temperature of the filaments. Inert gas, usually a combination of nitrogen and argon is filled in the bulb. The pressure inside the bulb under operating conditions is approximately atmospheric. Higher pressure means higher temperature. Less evapouration of the filament as gas exerts pressure..
Sonepat Slide: 52 Lamps below 40 watts may be of vacuum type and above 40 watts are gas filled. Why? According to combined gas law:- To increase temperature, either volume or pressure of the gas has to be increased. Can you do so in GLS?
Sonepat Slide: 53 If no gas is filled inside the shell, tungsten will get evapourated very soon. Therefore, some gas is to be filled. Nitrogen is cheap and inert but is very good conductor of heat. It will get heated up soon and may even melt the shell. Argon is poor conductor of heat and so cools the filament less.
Sonepat Slide: 54 Therefore, the gas is the mixture of argon and nitrogen. Adding 10% nitrogen in the mixture improves 1. life of the lamp 2.ultra violet emission 3.the bonding of barium & strontium. 4.lumens/watt.
Sonepat Slide: 55 Advantages: 1. Operates at unity power factor. 2. Operates directly on standard distribution of voltages. 3. Easily available in various shapes and shades. 4. It has good radiation characteristics in the luminous range and is 5. Not affected by the temperature of the surrounding air.
Sonepat Slide: 57 Arc Lamps: Current may be made to flow through two electrodes in contact with each other. When these are drawn apart an arc will strike between them. Such lamps may be; Carbon-Arc Flame Arc and Magnetic Arc.
Sonepat Slide: 58 Electric discharge lamps: The production of light is based on the phenomenon of excitation and ionisation in a gas or vapour. An atom has a positive nucleus and one or more electrons revolving around it in certain fixed orbits. They are known as free electrons.
Sonepat Slide: 59 Free electrons can be removed very easily from the atom. Electrons possess energy while leaving the atom. They have very less mass but high velocity. Kinetic energy = ½mv2. This energy can do some work. It can be transferred either by colliding or exciting.
Sonepat Slide: 60 The discharge lamp may use one of the following property. 1. Those in which the colour of the light is the same as produced by the discharge through the gas or vapour e.g. neon, mercury, sodium etc. 2. Those which use the phenomenon of fluorescence e.g. fluorescent lamps.
Sonepat Slide: 61 200 grams of mercury shall have 6.023×1023 atoms. Therefore, when we put 55 mg of mercury in the tube light, it means that the total number of mercury atoms are 1.656×1023. Each atom has 1 or 2 free electrons. Thus there are 165600000000000000000000 electrons available for participating in the process of giving light from a tube light.
Sonepat Slide: 63 Starter is used to start the discharge. High voltage is applied across the neon gas filled shell. Shell gets heated up and closes the nearby bi-metallic contact. Then current flows through the bi-metallic contact. Gas filled shell gets cool, opens the contact.
Sonepat Slide: 64 Choke: 1. Whenever starter breaks its contact, choke produces near about 1000V due to self induction. 2. This high voltage, starts the discharge. 3. Choke maintains 110V across the tube filaments. 4. It acts as a ballast means controls the current. 5. 110V drop inside the tube is a major waste.
Sonepat Slide: 65 Working: 1. When switch is put, electric current through the choke, one side electrode reaches to the neon gas filled shell. 2. Neon gas gets heated up, closes the nearby bimetallic contact. 3. Current passes to the second electrode & to the neutral. 4. Electrodes get heated up but neon gas cools, opens the contact. High voltage is applied by the choke across the electrodes.
Sonepat Slide: 67 5. Electric discharge takes place, free electrons starts moving towards other electrode. 6. Electrons collide with the atoms of inert gas. 7. Inert gas gets heated up, warms mercury. 8. Mercury changes to vapour, ejects electrons. 9. Electrons strike phosphor coated glass, gives up energy, returns back to parent atom.
Sonepat Slide: 68 9. Phosphor receives energy from the ejected electrons of mercury in the form of ultra- violet radiation. 10. Converts ultra-violet radiated energy into visible light of definite wavelength. 11. Phosphor have definite characteristics colours but when mixed together with other chemical they produce a large variety of colours.
Sonepat Slide: 69 Advantages of FTL: 1. 4 times higher light output than incandescent lamps. 2. Cheaper to operate. 3. Produces no heat. 4. Longer life up to 7500 hours. 5. Cool day & variety of colours. 6. 28% ultraviolet energy is converted into light.
Sonepat Slide: 70 Dis-advantages of FTL: 1. Lagging power factor even up to 0.5. 2. Complex fittings. 3. High initial cost. 4. Not suitable for extreme cold climatic conditions. 5. Causes radio interference. 6. Stroboscopic effect.
Sonepat Slide: 71 In AC since, the current passes through zero after every half cycle, the flow of electrons stops momentarily. A rapid flicker occur which gives rise to stroboscopic effect. Means moving machine may appear to be rotating in opposite direction. This is eliminated by using a capacitor or distributing the load in three phases.
Sonepat Slide: 74 A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb or an energy saving light bulb. It is a type of fluorescent lamp that screws into a regular light bulb socket or plugs into a small lighting fixture. CFL’s 1. have longer life (8000 hours) 2. consume less power (60 lumens/watt) 3. high initial cost gets recovered after 500 hours of use.
Sonepat Slide: 76 CFL’s was introduced in 1980’s. Due to improvement in product performance and reduction in its price, its demand is increasing. Magnetic ballasts have been replaced with electronic ballast. This has reduced flickering and slow starting associated with previous fluorescent lamps. Manufacturers make two types of CFL: 1. integrated type and 2. non-integrated type.
Sonepat Slide: 77 Integrated lamps combine; 1. a bulb 2. an electronic ballast and 3. screw fittings. These lamps are easy to replace incandescent bulbs. Non integrated lamps allow for replacement of consumable bulbs and re-using of electronic ballast.
Sonepat Slide: 78 CFL’s are produced for both ac & dc input. DC input CFL’s are used with battery or solar cells in cars, recreational vehicles and non- electrified areas. This replaces kerosene lanterns in villages & under developed areas. If this policy is encouraged by the government, villagers in India can have light in their houses using solar energy.
Sonepat Slide: 79 CFL’s are produced in varying shades of white. 1. Warm white (2700K) 2. Soft white (3500K) 3. Cool white (4100K) 4. Day light (6400K) The “K” alphabet denote the colour temperature in Kelvin. Colour temperature is a quantitative measure. The higher the number the cooler (bluer) the shade.
Sonepat Slide: 80 CFL’s are also produced, less commonly, in other colours. 1. Red, green and pink for inexpensive or general effect purposes. 2. Yellow for outdoor lighting, keeping insects away etc. 3. Black light for special effects.
Sonepat Slide: 81 There are mainly two parts in a CFL. 1. The gas filled tube (also called bulb or burner) and 2. Magnetic or electronic ballast. Electrical energy in the form of an electrical current from the ballast flows through the gas, causing it to give off ultraviolet light. The ultraviolet light then excites a white phosphor coating on the inside of the tube. The coating emits visible light.
Sonepat Slide: 82 Both the ballast and the burner are subject to failure from normal use. In low quality CFL’s, high temperature often cause the ballast electronics to fail before the burner. In high quality CFL’s, the burner almost always fail first.
Sonepat Slide: 83 The burners occasionally fails due to; 1. Cracks and imperfect seals. 2. Increased work function at the electrodes caused by vapourisation and sputtering-off the cathode material (deposition of ions on burner’s glass tubing) . 3. The sputtering-off of the cathode material on burner’s glass tubing causes blackening of the tube.
Sonepat Slide: 84 High quality electronics ballast can prolong the life of the burners by pre-heating the electrodes to prevent damage from rapid expansion. The best CFL lamps can even last up to 15,000 hours. For making such CFL’s, we need to have 1. high quality electronic ballast 2. Highly automated and controlled manufacturing. OSRAM is undoubtedly No-1 in the world today!
Sonepat Slide: 85 Colour Rendering Indexes (CRI): A CRI of 100 represents the most accurate reproduction of all colours such as the Sun. Good quality CFL manufacturers uses 3-4 types of phosphor which emits light in red, blue and green spectra to achieve white light. The CRI of this white light is around 80.
Sonepat Slide: 86 Time to achieve full brightness of CFL may take around 30 seconds or more. The other electric lamps; Incandescent lamps takes -- 0.1s LED’s take -- 0.01s. Sodium vapour takes -- 600s Mercury vapour -- 240-300s.
Sonepat Slide: 88 There are four basic types of HID lamps, each with its own characteristics. 1. Low pressure sodium vapour lamps 2. High pressure sodium vapour lamps 3. Mercury vapour lamps 4. Metal halide lamps All HID lamps consists of an arc tube enclosed in an bulb.
Sonepat Slide: 89 Sodium Vapour Lamps: Sodium vapour lamp is a gas discharge lamp which uses sodium in an excited state to produce light. There are two varieties of such lamps; 1. Low pressure/LPS/SOX 2. High pressure/HPS
Sonepat Slide: 91 The outer vacuum envelope of glass is coated with an infrared reflecting layer of indium-tin oxide, a semiconductor material that allows the visible light wavelengths out and keeps the infrared (heat) back. When the lamp is turned on it emits a dim red/pink light to warm the sodium metal and within a few minutes it turns into the common bright orange/yellow colour as the sodium metal
Sonepat Slide: 92 LPSV Lamps: 1. The low pressure sodium lamp gives light which is monochromatic. 2. Monochromatic means light of a particular wavelength of 590nm i.e. yellow. 3. In this colour, yellow and white will look yellow but all other shades of colours appears grey and black. 4. These lamps are used only for street and highway lighting.
Sonepat Slide: 93 5. It is the most efficient electrical lamps source which gives up to 200 lumens/watt. 6. The light producing arc contains a small amount of argon and neon which assist in discharge. 7. The space between the arc tube and outer tube is under vacuum. 8. The pressure inside the are tube is 10-3mm of Hg.
Sonepat Slide: 94 9. It has to have large physical size. 10.The temperature inside the arc tube is around 260°C. 11.They are less effective in directing and controlling a light beam. 12.Therefore, it needs to be mounted at lower heights with limitations. 13.It takes about 10 minute for the sodium vapour to give its own yellow light.
Sonepat Slide: 95 High pressure sodium vapour lamps: 1. These are smaller in diameter. 2. High temperature inside the arc tube. 3. The pressure inside the arc tube is around 20mm of Hg. 4. It contains little quantity of mercury also. 5. Due to the presence of mercury, it gives out non-monochromatic light.
Sonepat Slide: 96 6. They are quite efficient i.e. 100 lumens/watt. 7. The lamp may be mounted in any position. 8. Used for outdoor or security lighting, 9. No cooling time is required. 10.Longer life up to 25000 hours.
Sonepat Slide: 98 Sodium and mercury provides the vapour in which the arc is drawn. The temperature of the lamp depends upon the lamp wattage. The higher the temperature the higher will be the mercury and sodium vapor pressures in the lamp. An increase in these metal pressures will cause a decrease in the electrical resistance of the lamp.
Sonepat Slide: 99 For a given voltage, there are generally three modes of operation: the lamp is extinguished and no current flows the lamp is operating, with mixture of liquid sodium and mercury in the tube the lamp is operating with all mixture of liquid sodium and mercury evapourated
Sonepat Slide: 100 HP Mercury vapour lamps: 1. There are 3 electrodes, 2 main & 1 auxiliary. 2. The auxiliary electrode is used for starting the discharge. 3. Neon gives red, sodium yellow and mercury vapour in four distinct lines in visible and two in ultra-violet region. 4. The pressure inside the arc tube is around 25- 50 mm of Hg.
Sonepat Slide: 102 5. The lamp requires 4-5 minute to attain its full brilliancy. 6. This lamp even operates at an extra high pressure of 5 to 10 atmosphere. 7. The efficiency is about 50 lumens/watt. 8. The outer envelop is filled with argon & nitrogen mixture.
Sonepat Slide: 103 Light emitting diode: 1. When current flows, it emits light. 2. The light’s intensity depends upon the current 3. Used as indicators and for displays. 4. Consumes power around 10 to 150 mW. 5. Has life span of 100,000 hours. 6. Switching time remains about 1ns.
Sonepat Slide: 105 Halogen lamps: 1. This also uses a tungsten filament lamp. 2. The bulb is filled with inert gas plus less than 1% of halogen gas such as iodine, bromine, fluorine etc. 3. The bulb is made of quartz to withstand high pressure & temperature i.e. 1500K. 4. The lumen per watt remains 20. 5. Has life of 2500-3000 hours.
Sonepat Slide: 107 6. The deposited tungsten molecules on the glass wall reacts with halogen when temperature is 250°C making tungsten halide. 7. Tungsten halide near lamp filament due to high heat gets separated. Tungsten returns back to filament. 8. This cycle is called tungsten-halogen cycle and maintains constant light output. 9. This is possible only when the shape is cylindrical and close to filament.
Sonepat Slide: 108 Why is halogen lamps better than GLS? the filament temperature can be increased, giving a whiter light output the depreciation in light output with time is greatly decreased; and the lumen output and the life are increased.
Sonepat Slide: 109 Neon lamps: 1. These lamps belong to cold cathode category. 2. The electrodes are in the form of iron shells and are coated from inside. 3. The colour of the emitted is red. 4. These lamps are used mostly for electrical advertisements.
Sonepat Slide: 111 Metal halide lamps: A high-intensity discharge light source in which the light is produced by the radiation from mercury, together with halides of metals such as sodium and scandium produces a very efficient white light output. Halide means A mineral compound characterized by a halogen such as fluorine, chlorine, iodine, or bromine as the anion. NaCl is an example of a halide.
Sonepat Slide: 112 1. Metal halide lamps were discovered in 1960. 2. It has nearly twice the efficacy of mercury vapour lamps. 3. They give white light with a strong blue-green components, which is good for night vision. 4. The metal halide lamp is a development of the medium pressure mercury arc lamp.
Sonepat Slide: 113 5. Addition of some rare earth metals and iodides produces specific light output emissions. They are alternative to mercury vapour lamps. 6. Earth metals are beryllium, strontium etc. 7. Operating life is around 10,000 hours. 8. These lamps are widely used in the graphic arts, printing, industrial applications etc.
Sonepat Slide: 119 Colour Temperature (K) Example Colour Temperature (K) Example 1700 Matchstick 5500 Electronic Flash 1850 Candle 6500 Day Light 2800 GLS 9300 TV Screen 3400 Studio Lamps 30,000 Lightening Some examples of colour temperature