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MEAN Horizontal CANDLE Power (M.H.C.P) is the mean of the candle powers in all directions in the horizontal plane PASSING through the SOURCE of light.

Mean Horizontal Candle Power (M.H.C.P) is the mean of the candle powers in all directions in the horizontal plane passing through the source of light.

Total flux = (4 π × total CANDLE POWER) Lumens = ( 4 × 3.1421 × 60) Lumens = 754.2 Lumens.

Total flux = (4 π × total candle power) Lumens = ( 4 × 3.1421 × 60) Lumens = 754.2 Lumens.

Foot CANDLE or LUMEN per SQUARE foot is defined as the illumination produced on the inner surface of a hollow sphere of a hollow sphere of radius one foot by a POINT surface at the center of intensity of one candela.

Metre-candle or Lux (Lumen/m^2) is defined as the illumination produced on the inner surface of a hollow sphere of radius one meter by a point surface at the center of UNIFORM intensity of one candela.

Foot candle or Lumen per square foot is defined as the illumination produced on the inner surface of a hollow sphere of a hollow sphere of radius one foot by a point surface at the center of intensity of one candela.

Metre-candle or Lux (Lumen/m^2) is defined as the illumination produced on the inner surface of a hollow sphere of radius one meter by a point surface at the center of uniform intensity of one candela.

The light COMING out from a standard CANDLE used as the unit of illuminating power of a LIGHTING SOURCE is called standard candle power.

The light coming out from a standard candle used as the unit of illuminating power of a lighting source is called standard candle power.

A standard CANDLE is that weighs 1/6 pound of pure spermaceti wax and burning at the rate of 120 grains per hour i.e. 7.776 GRAMS per hour.

A standard candle is that weighs 1/6 pound of pure spermaceti wax and burning at the rate of 120 grains per hour i.e. 7.776 grams per hour.

The luminous flux falling PER unit AREA on a SURFACE is KNOWN as illumination and is expressed in Lumen/m2.

The luminous flux falling per unit area on a surface is known as illumination and is expressed in Lumen/m2.

Luminous FLUX emitted by the sources per UNIT SOLID angle in any particular direction is KNOWN as the luminous intensity.

Luminous flux emitted by the sources per unit solid angle in any particular direction is known as the luminous intensity.

Lumen is the unit of luminous flux which is EQUAL to the flux emitted per unit SOLID angle from a UNIFORM source of one candle POWER.

1 lumen = 0.0016 watt (approx).

Lumen is the unit of luminous flux which is equal to the flux emitted per unit solid angle from a uniform source of one candle power.

1 lumen = 0.0016 watt (approx).

LUMINOUS flux is the LIGHT energy radiated per second from a luminous BODY in the form of light waves. It is MEASURED in lumen.

Luminous flux is the light energy radiated per second from a luminous body in the form of light waves. It is measured in lumen.

Light is a form of ENERGY, which is radiated by heated BODIES. The light is the part of the RADIANT energy which PRODUCES a sensation (of light) on the human eye.

Light is a form of energy, which is radiated by heated bodies. The light is the part of the radiant energy which produces a sensation (of light) on the human eye.

Specular reflection means the reflection on some in the form of a BEAM of light but not SCATTERED. In this reflection, unless the eye is placed in the PATH of the reflected beam the viewer is unaware of the existence of light.

Diffuse reflection means the reflection of light energy in the scattered form in all direction. In this reflection, the viewer can SEE the illuminated surface but not the light source.

Specular reflection means the reflection on some in the form of a beam of light but not scattered. In this reflection, unless the eye is placed in the path of the reflected beam the viewer is unaware of the existence of light.

Diffuse reflection means the reflection of light energy in the scattered form in all direction. In this reflection, the viewer can see the illuminated surface but not the light source.

Local lighting means an INTENSE illumination on some particular POINTS by means of adjustable fittings. In this lighting scheme lamps are mounted in deep REFLECTORS to avoid GLARE.

Local lighting means an intense illumination on some particular points by means of adjustable fittings. In this lighting scheme lamps are mounted in deep reflectors to avoid glare.

In this lighting SCHEME lamps made of DIFFUSING glass are EMPLOYED which give almost equal distribution of LIGHT in all direction.

In this lighting scheme lamps made of diffusing glass are employed which give almost equal distribution of light in all direction.

In this lighting scheme the light comes partly from the ceiling by DIFFUSED reflection and party direct from the SOURCE on the working SURFACE. As it is glare free with soft shadows it is mainly used for indoor light DECORATION PURPOSES.

In this lighting scheme the light comes partly from the ceiling by diffused reflection and party direct from the source on the working surface. As it is glare free with soft shadows it is mainly used for indoor light decoration purposes.

In this lighting scheme the total light flux is made to FALL downwards directly with the help of semi-direct REFLECTOR on the working surface and also to illuminate the ceilings and WALLS. It is BEST suited to rooms with high ceilings where a high level of UNIFORMLY distributed illumination is desirable.

In this lighting scheme the total light flux is made to fall downwards directly with the help of semi-direct reflector on the working surface and also to illuminate the ceilings and walls. It is best suited to rooms with high ceilings where a high level of uniformly distributed illumination is desirable.

In this lighting SCHEME the light does not reach the surface directly from the source, maximum light is thrown upwards to the ceiling from which it is distributed all over the room by diffuse reflectance. The glare being reduced the resulting illumination becomes softer. It is used for decoration PURPOSES in cinemas, theaters, and hotels etc. and in workshops where LARGE machines and other obstructions would CAUSE troublesome shadows if direct lighting is employed.

In this lighting scheme the light does not reach the surface directly from the source, maximum light is thrown upwards to the ceiling from which it is distributed all over the room by diffuse reflectance. The glare being reduced the resulting illumination becomes softer. It is used for decoration purposes in cinemas, theaters, and hotels etc. and in workshops where large machines and other obstructions would cause troublesome shadows if direct lighting is employed.

• Production factor INCREASES
• Accident DECREASES
• WASTAGE of products decreases.

The factors are as follows: 

•  Illumination level
• Glare
• Shadow
• Space HEIGHT ratio
• Mounting height of the lamp
• Area to be illuminated
• COLOUR of surrounding walls
• MOVEMENT of the object
• Utilization factor and 
• DEPRECIATION factor.

The factors are as follows: 

• Nature of the work
• Architectural DESIGN
• SURROUNDINGS
• Nature of LIGHT and 
• MAINTENANCE.

• The light should not strike directly the eyes.
• The type and size of the LAMP should be CORRECT.
• PROPER location should be made.
• REFLECTING equipment should be SUITABLE for purpose.
• Hard and long shadows should be avoided.

It is the RATIO of illumination under normal condition of old INSTALLATION to the illumination under ideal condition of new installation.

It is the ratio of illumination under normal condition of old installation to the illumination under ideal condition of new installation.

The FLUX EMITTED per unit area of the source in a direction at right ANGLES to the SURFACE is known as brightness. Its unit is CANDLES / m2 or candles / 〖cm〗2 or candles / 〖ft〗2.

The flux emitted per unit area of the source in a direction at right angles to the surface is known as brightness. Its unit is candles / m2 or candles / 〖cm〗2 or candles / 〖ft〗2.

HARD and long shadows are avoided by

• Using LARGE numbers of small luminaires mounted over a minimum height of 2.5 metres.
• Using wide surface SOURCES of light by using diffusing globe over filament LAMP or by using indirect lighting system.

Hard and long shadows are avoided by

DUE to its UNSYMMETRICAL SHAPE.

Due to its unsymmetrical shape.

A polar CURVE is a convenient way of SHOWING how the candle power of a lamp varies in different directions. Polar CURVES are used to determine the M.H.C.P.,M.S.C.P. and the ACTUAL ILLUMINATION of a surface by employing the candle power in the particular direction.

A polar curve is a convenient way of showing how the candle power of a lamp varies in different directions. Polar curves are used to determine the M.H.C.P.,M.S.C.P. and the actual illumination of a surface by employing the candle power in the particular direction.

Glare means the BRIGHTNESS within the FIELD of vision of such a character as to cause ANNOYANCE, discomfort, INTERFERENCE with vision or eye fatigue.

Glare means the brightness within the field of vision of such a character as to cause annoyance, discomfort, interference with vision or eye fatigue.

Specular reflection means the reflection on some in the form of a beam of light but not scattered. In this reflection unless the EYE is placed in the path of the reflected beam the VIEWER is unaware of the existence of light.

Diffuse reflection means the reflection of light energy in the scattered form in all direction. In this reflection the viewer can see the ILLUMINATED surface but not the light SOURCE.

Specular reflection means the reflection on some in the form of a beam of light but not scattered. In this reflection unless the eye is placed in the path of the reflected beam the viewer is unaware of the existence of light.

Diffuse reflection means the reflection of light energy in the scattered form in all direction. In this reflection the viewer can see the illuminated surface but not the light source.

INCANDESCENT lamp WORKS by the heating EFFECT of electricity.

Incandescent lamp works by the heating effect of electricity.

The causes are as FOLLOWS:-

1. Coiled COIL FILAMENT is mechanically stronger.
2. It can operate at high TEMPERATURE.
3. It gives greater output.
4. It gives greater EFFICIENCY.

The causes are as follows:-

• STRAIGHT WIRE TYPE
• COILED type and
• Coiled-coil type.

MELTING POINT is 3400°C and WORKING TEMPERATURE is about 2000°C.

Melting point is 3400°C and working temperature is about 2000°C.

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.

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.

TUNGSTEN, TANTALUM and CARBON.

Tungsten, Tantalum and Carbon.

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.

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.

The two TYPES of incandescent LAMPS are:-

• Metal FILAMENT lamps &
• Carbon filament lamps.

The two types of incandescent lamps are:-

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.

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.

There are types of lamps for producing light by ELECTRICITY.

• INCANDESCENT lamp
• Electric ARC lamp and
• Gas discharge lamp.

There are types of lamps for producing light by electricity.

An ELECTRIC lamp is a glass 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.

An electric lamp is a glass 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.

Halogen lamp is the latest member in the family of incandescent lamp possessing numerous advantages over the ordinary incandescent lamp. Halogens area group CONSISTING of the elements fluorine, chlorine, bromine and iodine. The life and efficiency of an ordinary incandescent lamp are affected by the gradual evaporation of tungsten and also its operating temperature. The addition of a small amount of any halogen vapour to the argon gas filing of a lamp has the effect that under certain conditions the metal evaporated from the tungsten filament on reaching the relatively low temperature near the wall of the envelope forms a compound of tungsten halogen and being very voltage tungsten halogen suffers from thermal diffusion in the direction of filament and on reaching the filament at high temperature it decomposes into the tungsten and halogen. In this way the evaporated tungsten is returned back and restored to the filament by means of a chemical reaction. Halogen therefore works as a transport gas. This regenerative cycle MAINTAINS the interior of the bulb in a clean condition without depositing any metal vapor on the wall. The action requires a higher bulb temperature of about 250℃ that can be withstood by the glass. Therefore a relatively expensive material QUALITY is chosen as the envelope material and its size is kept very small in which high gas filling pressure in made possible. This gives long life of about 2000 hours to the lamp with higher light output of about 22-23 lumens/watt.

Halogen lamps are made in the standard WATTAGE of 300 W, 500 W, 600 W, 1000 W, 1500 W & 2000 W but sometimes these are made upto 5 kW. These lamps are suitable for outdoor illumination of buildings, sports grounds, parks, air ports, fountains etc. and also used in public halls, sports halls, factories, photo film, T.V. studios, overhead projectors, car lighting, signaling etc.

Halogen lamp is the latest member in the family of incandescent lamp possessing numerous advantages over the ordinary incandescent lamp. Halogens area group consisting of the elements fluorine, chlorine, bromine and iodine. The life and efficiency of an ordinary incandescent lamp are affected by the gradual evaporation of tungsten and also its operating temperature. The addition of a small amount of any halogen vapour to the argon gas filing of a lamp has the effect that under certain conditions the metal evaporated from the tungsten filament on reaching the relatively low temperature near the wall of the envelope forms a compound of tungsten halogen and being very voltage tungsten halogen suffers from thermal diffusion in the direction of filament and on reaching the filament at high temperature it decomposes into the tungsten and halogen. In this way the evaporated tungsten is returned back and restored to the filament by means of a chemical reaction. Halogen therefore works as a transport gas. This regenerative cycle maintains the interior of the bulb in a clean condition without depositing any metal vapor on the wall. The action requires a higher bulb temperature of about 250℃ that can be withstood by the glass. Therefore a relatively expensive material quality is chosen as the envelope material and its size is kept very small in which high gas filling pressure in made possible. This gives long life of about 2000 hours to the lamp with higher light output of about 22-23 lumens/watt.

Halogen lamps are made in the standard wattage of 300 W, 500 W, 600 W, 1000 W, 1500 W & 2000 W but sometimes these are made upto 5 kW. These lamps are suitable for outdoor illumination of buildings, sports grounds, parks, air ports, fountains etc. and also used in public halls, sports halls, factories, photo film, T.V. studios, overhead projectors, car lighting, signaling etc.

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.

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.

Arc LAMP can be used on a.c. SUPPLY at its WORKING VOLTAGE of about 55 volts.

Arc lamp can be used on a.c. supply at its working voltage of about 55 volts.

About 45 VOLTS.

About 45 Volts.

CINEMA PROJECTORS and SEARCH LIGHTS.

Cinema projectors and search lights.

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.

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.

CARBON ARC, flame arc and magnetite arc the forms of arc lamps of which the carbon arc lamp is most USUAL FORM.

Carbon arc, flame arc and magnetite arc the forms of arc lamps of which the carbon arc lamp is most usual form.

In an ARC lamp a current flows between two ELECTRODES which are drawn apart RESULTING an arc being struck in between them. The arc MAINTAINS the current and becomes very efficient SOURCE of light.

In an arc lamp a current flows between two electrodes which are drawn apart resulting an arc being struck in between them. The arc maintains the current and becomes very efficient source of light.

In discharge lamps cathodes EMITTING electrons by HEAT are TERMED as hot cathodes and where no heating is EMPLOYED they are called as cold cathodes.

In discharge lamps cathodes emitting electrons by heat are termed as hot cathodes and where no heating is employed they are called as cold cathodes.

• High INITIAL cost
• Low power factor
• Complicated starting requires choke to give voltage surge and to limit the current
• Condenser is required to improve power factor
• Full brilliancy comes after a CONSIDERABLE time
• These cannot be used in any position
• Light output fluctuates producing stroboscopic EFFECT
• Multiple images are formed on the MOVING objects.

Gas DISCHARGE LAMPS are preferred to INCANDESCENT lamps due to higher efficiency, longer life, the better color of lighting and uniform INTENSITY of LIGHT.

Gas discharge lamps are preferred to incandescent lamps due to higher efficiency, longer life, the better color of lighting and uniform intensity of light.

IONISATION of GAS.

Ionisation of gas.