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Rahul Singhmar
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Topics
- Definitions
- Illumination
- Illumination factors
- Lighting scheme
- Different types of Electric lamps
- Question answer on electric lamps
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Definitions
- Light
It is defined as the radiant energy from hot bodies which produces the visible sensation upon the human eye.- Lumen
One lumen is the luminous flux emitted by a point source of one candle power per unit solid angle.- Solid Angle
The solid angle is measured in sterdians .It is the angle generated by the surface passing through the point space and periphery of the area.
- Luminous Intensity
It is the amount of luminous flux emitted by a source per unit solid angle.It is measured in candela.
- Illumination
It is the luminous flux received by a surface per unit area of surface.- Candle power
The candle power of a source of light in any directions is the number of lumens per unit solid angle in that direction.- Plane angle
It is subtended at a point in a plane by two converging lines and it's magnitude is given byAngle is equal to arc per radius radians.
- Depreciation factor
The efficiency of a projector lamp is seriously affected by the dust and dirt which accumulate on the projector lamp during its course of use.So these must be cleaned at regular intervals.
What are the laws of illumination ?
i) Illumination is directly proportional to the luminous intensity of the source.
ii) Inverse square law – The illumination of a surface receiving its flux from a point source is inversely proportional to the square of the distance between the surface and the source.
iii) Lambert’s cosine law – The illumination of a surface at any point is proportional to the cosine of the angle between the normal at the point and the direction of the luminous flux.
What are the factors which affect the correct illumination ?
(a) Nature of the work, (b) Architectual design, (c) Surroundings, (d) nature of light and (e) Maintenance.What are the factors to be considered in the design of a lighting scheme ?
The factors are as follows:i) Illumination level,
ii) Glare,
iii) Shadow,
iv) Space height ratio,
v) Mounting height of the lamp,
vi) Area to be illuminated,
vii) Colour of surrounding walls,
viii) Movement of the object,
ix) Utilization factor and
x) Depreciation factor.
Electric lamp
An electric lamp is a conventional light emitting component used in different circuits, mainly for lighting and indicating purposes. The construction of lamp is quite simple, it has one filament surrounding which, a transparent glass made spherical cover is provided. The filament of the lamp is mainly made of tungsten as it has high melting point temperature. A lamp emits light energy as the thin small tungsten filament of lamp glows without being melted, while current flows through it.Uses of Electric Lamps
These lamps are mainly get used for lighting and indicating purpose. Although, now a days use of light emitting diodes LEDs for these two purposes dominates uses of conventional lamps. But still they are in use although at maximum places they are replaced by LEDs.
How does a carbon arc lamp work?
In a carbon arc lamp, the electrodes are carbon rods in free air. To ignite the lamp, the rods are touched together, thus
allowing a relatively low voltage to strike the arc. The rods are then slowly drawn apart, and electric current heats and maintains an arc across the gap.
What was the arc lamp used for?
Arc Lamp. Invented decades before it could be used, the first type of electric light was so brilliant it was used for lighthouses and street lamps. An arc lamp produces light by the sparking (an electrical arc) of a high current between two conducting electrodes, usually carbon rods.
What are the forms of arc lamps ?
Carbon arc, flame arc and magnetite arc the forms of arc lamps of which the carbon arc lamp is most usual form.
What do you know about carbon arc lamp ?
Carbon arc lamps have electrodes of hard carbon placed and to end and connected to a d.c. source. When the current flows through them the ends of carbon rods become incandescent due to high resistance. If they are pulled slightly apart about 2-3 cm distance an arc will be formed between two carbon rods producing white light. The arc consists of carbon vapour surrounded by an orange red zero of burning carbon and pale green flames. The arc is maintained by the transfer of carbon particles from positive carbon rod to negative one. It is necessary to maintain the carbons at a constant distance apart otherwise there will be decrease in illumination due to burning of positive carbon. The luminous efficiency of carbon arc lamp is about 9 lumens per watt.
What are the main applications of carbon arc lamps ?
Cinema projectors and search lights.
What is the working voltage across d.c. arc lamp ?
About 45 Volts.Can we use arc lamp on a.c supply and what is its working voltage ?
Arc lamp can be used on a.c. supply at its working voltage of about 55 volts.
What is carbon filament lamp ?
In this type of lamp the filament is made of carbon. The melting point of carbon is 3500℃ but its working temperature should not exceed 1800℃ because at high temperature it starts disintegrating and blackens the inside of the bulb. Its temperature Co-efficient is negative. So the resistance decreases at high temperature and taken more current resulting high power consumption. The efficiency of this lamp is low of about 4 lumens per watt. It gives yellowish light. It is generally used for heating purposes and to create a voltage drop for example in battery charging but not for lighting purpose.The approximate life of this lamp is about 800-900 hours.
What is fluorescent lamp?
When the fluorescent tube is switched on almost full supply voltage is applied to the starter. The potential across bimetallic electrodes of the starter causes a small glow discharge at a small current not enough to heat up the tube filaments. This discharge is enough to heat the bimetallic strips of the starter itself causing them to bend and make contact. As a result, the large current flows through the electrodes their temperature being raised to incandescence and the gas in the immediate neighborhood inside the tube gets ionized. At the same time when the contacts of the starter are closed potential difference across it is reduced to zero. After two or three seconds glow discharge inside the starter stops and the bimetallic strips cool down which breaks the contacts apart. This sudden break induces a very high voltage in the coke connected in series due to its inertia effect and it is sufficient to initiate the discharge in the main tube light. When the fluorescent tube is alight, current passes through the tube which offers a very low resistance. The voltage across the tube is about 110 volts and rest of the supply voltage of about 110 volts is dropped in the choke. Due to the low voltage, the starter ceases to glow. Starters are so designed that this potential difference across the lamp in running condition is insufficient to restart the glow discharge in the starter. So the contacts remain open, thus the tube is put in operation.
What is an electric lamp and incandescent lamp ?
What is an electric lamp?
An electric lamp is a gllas bulb, often filled with nitrogen or some other chemically inactive gas containing a wire or filament usually made of tungsten in which the passage of an electric current through the filament heats it to a white heat and then to the visible radiation i.e. light.
What are the types of lamps ?
There are types of lamps for producing light by electricity. Incandescent lamp, b) Electric arc lamp and c) Gas discharge lamp.What do you mean by incandescent lamp ?
The incandescent or filament type consists of a file metallic wire of high resistance known as filament enclosed in an evacuated glass globe. When the electric current passes through the filament, heat is produced and the temperature of the filament increases. At high temperature, it radiates heat as well as light energy thereby producing electric lights by incandescence of a heated filament.What are the types of incandescent lamps?
The two types of incandescent lamps are - (a) Metal filament lamps & (b) Carbon filament lamps.What should be the properties of metal as a filament in the incandescent lamp ?
It should have high melting point, low vapour pressure, high resistivity and low-temperature coefficient. It should be ductile and mechanically very strong to withstand vibrations during normal use.
Which materials are used for the filament of the incandescent lamps ?
Tungsten, Tantalum and Carbon.
Which material is mostly used for the filament of incandescent lamps and why ?
Tungsten is widely used for the filament of the incandescent lamp due to its high-temperature co-efficient, high melting point, low vapour pressure, ductility and good mechanical strength.
What are the melting point and working temperature of the tungsten filament?
Melting point is 3400°C and working temperature is about 2000°C.
What are the types of filaments normally used?
(a) Straight wire type, (b) Coiled type and (c) Coiled-coil type.
Why are the modern incandescent lamps made of coiled filament?
The causes are as follows :-
Coiled coil filament is mechanically stronger.
It can operate at high temperature.
It gives greater output.
It gives greater efficiency.
On which principle does the incandescent lamp work?
Incandescent lamp works by the heating effect of electricity.What is a gas discharge lamp ?
What do you know about the working of a gas discharge lamp ?
A gas discharge lamp consists of a transparent gas discharge enclosure containing a small quantity of gas or vapour at a low pressure and two electrodes provided for connecting the lamp to the supply mains. When the electrodes establish a potential difference, the gas gets ionized. Consequently, an electrical current flows and a luminous discharge is obtained from the excited atom of gas.
What is the basic principle of gas discharge lamp ?
Ionisation of gas.Why are gas discharge lamps preferred to incandescent lamps ?
Gas discharge lamps are preferred to incandescent lamps due to higher efficiency, longer life, the better color of lighting and uniform intensity of light.
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