Interview Questions.

Top 100+ Illumination Interview Questions And Answers

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Top 100+ Illumination Interview Questions And Answers

Question 1. What Do You Mean By Stroboscopic Effect? How Is This Effect Eliminated In Fluorescent Tube Lighting?

Answer :

All gasoline discharge lamps operated on a 50 Hz alternating present day supply are virtually flickering on and off 100 instances per second. In ordinary conditions, the human eye does no longer be aware the fact. But whilst a shifting item like rotating elements of equipment is followed, at the positive pace it may seem like stationary or moving in collection of jerks or rotating slowly than its real velocity. This effect of manufacturing an illusion of truth is known as the stroboscopic impact and this is obviously a possible source of risk in factories, gadget stores and so forth.

In fluorescent tube lights the stroboscopic impact can be eliminated both with the aid of the usage of a three lamp unit wherein every lamp is connected to a separate section of a 3 section, four cord supply or by using a -lamp unit in single phase supply each having its very own choke however there's best one condenser related in collection with one of the lamps.

Question 2. Why The Power Factor Of Tube Circuit Low And What Is Is The Value Of The Power Factor?

Answer :

Due to the presence of inductive choke the strength component of the tube lamp is set 0.50.

Electrical and Electronics Engineering Interview Questions
Question three. What Is The Starting And Running Current Of The Fluorescent Tube?

Answer :

zero.55 A and zero.37 A for 20 W, zero.Sixty five A and 0.43 A for 40W, 1.00 A and zero.Sixty seven A for sixty five W & 1.Three A and zero.87 A for eighty W respectively.

Question four. What Are The Available Sizes Of Fluorescent Tubes?

Answer :

38 cm (15”) for 14 watts
46 cm (18”) for 15 W
61 cm (2”) for 20 W
one hundred cm (three’- 37/8 “) for 25 W
122 cm (four’) for 40 W
a hundred twenty five cm (five’)for sixty five W and
one hundred twenty five cm (five’) for eighty W
Question five. What Is A Fluorescent Tube?

Answer :

When the fluorescent tube is switched on nearly full deliver voltage is implemented to the starter. The capacity throughout bimetallic electrodes of the starter causes a small glow discharge at a small modern-day not sufficient to warmness up the tube filaments. This discharge is sufficient to heat the bimetallic strips of the starter itself inflicting them to bend and make contact. As a result, the big contemporary flows through the electrodes their temperature being raised to incandescence and the gas within the on the spot neighborhood within the tube receives ionized. At the identical time while the contacts of the starter are closed potential difference across it's miles decreased to zero. After  or three seconds glow discharge inside the starter stops and the bimetallic strips calm down which breaks the contacts aside. This unexpected break induces a completely excessive voltage inside the coke linked in collection because of its inertia effect and it is sufficient to initiate the release within the fundamental tube mild. When the fluorescent tube is a mild, modern passes via the tube which offers a totally low resistance. The voltage throughout the tube is about 110 volts and relaxation of the supply voltage of approximately 110 volts is dropped in the choke. Due to the low voltage, the starter ceases to glow. Starters are so designed that this capacity distinction across the lamp in running circumstance is insufficient to restart the glow discharge in the starter. So the contacts continue to be open, accordingly the tube is put in operation.

Electronic Circuits Interview Questions
Question 6. Why Is A Condenser Connected In Parallel With The Starter Of A Fluorescent Tube?

Answer :

To suppress the radio interference a condenser of about 0.05 μF capacity is connected in parallel with the starter.

Question 7. Why Is A Resistance Connected In Series With The Radio Suppressor Condenser?

Answer :

A resistance of approximately a hundred ohms is connected in collection with the radio suppressor condenser to test the condenser surges in order to prevent the starter contacts welding together.

Electrical Engineering Interview Questions
Question eight. Why Is A Condenser Connected Across The Supply Line In Fluorescent Tube Circuit?

Answer :

To enhance the electricity aspect a condenser is hooked up across the deliver line. The size of the condenser must be 3.25μF for 40 watt and seven.5 μF for eighty watt lamps.

Question nine. Is The Choke Necessary For Tube Light Working In D.C. Circuit?

Answer :

Yes, the choke is essential to create the voltage impulse on the time of beginning.

ELECTRONICS & INSTRUMENTATION Engineering Interview Questions
Question 10. Why Is An Extra Variable Resistance Connected In Series With The Choke On D.C. Supply?

Answer :

As there's no impact of inductance on D.C. Deliver an extra variable resistance is attached in collection with the choke to boom the effective resistance to soak up the distinction between the mains voltage and the perfect lamp voltage all through jogging.

Question eleven. Why Is A Reversing Switch Used For Fluorescent Tube Light In D.C. Circuit?

Answer :

A reversing transfer is used to opposite the cutting-edge at periods to prevent the blackening of the tube at high-quality end due to migration of the mercury from the tremendous give up to the negative end of the tube.

Electrician Assistant Interview Questions
Question 12. Which Lamp Will Give More Of Incandescent Lamp And Fluorescent Tube Light For The Same Wattage?

Answer :

Fluorescent tube light.

Electrical and Electronics Engineering Interview Questions
Question 13. Why Are Fluorescent Lamps Most Commonly Used?

Answer :

Fluorescent lamps are maximum usually used because of its following advantages over different light sources :-

Increased efficiency
Longer lifestyles of lamp
Gives illumination in a ramification of colors
Gives glare or glitter unfastened mild
High lighting fixtures intensities are completed without immoderate temperature rise
Gives diffused and shadow light
Gives more comfy illumination and
Through initial fee is extra it's miles reasonably-priced.
Question 14. Why Is Light Efficiency High In Fluorescent Tube Lights?

Answer :

The mild efficiency in fluorescent tube mild is excessive because the invisible radiation is transformed into visible radiation with the motion of phosphor coating within the tube which reduces the loss light strength.

Question 15. What Do You Know About The Working Of A Gas Discharge Lamp?

Answer :

A fuel discharge lamp consists of a transparent gas discharge enclosure containing a small amount of fuel or vapour at a low pressure and  electrodes provided for connecting the lamp to the deliver mains. When the electrodes establish a capacity distinction, the gas gets ionized. Consequently, an electrical present day flows and a luminous discharge is acquired from the excited atom of fuel.

Electrician Interview Questions
Question 16. What Is The Basic Principle Of Gas Discharge Lamp?

Answer :

Ionisation of gasoline.

Question 17. Why Are Gas Discharge Lamps Preferred To Incandescent Lamps?

Answer :

Gas discharge lamps are preferred to incandescent lamps due to higher performance, longer lifestyles, the higher colour of lighting and uniform intensity of light.

Electrical Power System Interview Questions
Question 18. What Are The Demerits Of A Gas Discharge Lamp?

Answer :

High preliminary price
Low power issue
Complicated starting requires choke to give voltage surge and to limit the modern
Condenser is needed to enhance energy element
Full brilliancy comes after a considerable time
These can't be used in any function
Light output fluctuates producing stroboscopic impact
Multiple snap shots are shaped on the shifting gadgets.
Electronic Circuits Interview Questions
Question 19. What Do You Mean By Hot Cathodes And Cold Cathodes?

Answer :

In discharge lamps cathodes emitting electrons by way of warmness are termed as warm cathodes and where no heating is employed they're referred to as as cold cathodes.

Question 20. How Does An Arc Lamp Work?

Answer :

In an arc lamp a current flows between two electrodes which are drawn aside ensuing an arc being struck in among them. The arc keeps the current and turns into very green source of mild.

Electrical Drives Interview Questions
Question 21. What Are The Forms Of Arc Lamps?

Answer :

Carbon arc, flame arc and magnetite arc the types of arc lamps of which the carbon arc lamp is maximum regular shape.

Question 22. What Do You Know About Carbon Arc Lamp?

Answer :

Carbon arc lamps have electrodes of hard carbon positioned and to cease and connected to a d.C. Source. When the present day flows thru them the ends of carbon rods grow to be incandescent due to high resistance. If they may be pulled barely apart approximately 2-3 cm distance an arc may be shaped between  carbon rods generating white light. The arc includes carbon vapour surrounded by means of an orange crimson 0 of burning carbon and faded green flames. The arc is maintained by way of the switch of carbon debris from fine carbon rod to bad one. It is essential to hold the carbons at a regular distance aside in any other case there will be lower in illumination because of burning of positive carbon. The luminous efficiency of carbon arc lamp is ready 9 lumens in step with watt.

Question 23. What Are The Main Applications Of Carbon Arc Lamps?

Answer :

Cinema projectors and search lights.

Question 24. What Is The Working Voltage Across D.C. Arc Lamp?

Answer :

About forty five Volts.

Electrical Engineering Interview Questions
Question 25. Can We Use Arc Lamp On A.C Supply And What Is Its Working Voltage?

Answer :

Arc lamp can be used on a.C. Supply at its running voltage of approximately fifty five volts.

Question 26. What Is Carbon Filament Lamp?

Answer :

In this type of lamp the filament is made from carbon. The melting point of carbon is 3500? however its working temperature should no longer exceed 1800? because at high temperature it starts disintegrating and blackens the internal of the bulb. Its temperature Co-efficient is bad. So the resistance decreases at excessive temperature and taken more contemporary resulting excessive strength intake. The efficiency of this lamp is low of about 4 lumens consistent with watt. It offers yellowish light. It is generally used for heating purposes and to create a voltage drop for instance in battery charging however now not for lights purpose. The approximate life of this lamp is about 800-900 hours.

Question 27. What Is A Halogen Lamp?

Answer :

Halogen lamp is the trendy member within the family of incandescent lamp owning severa blessings over the everyday incandescent lamp. Halogens place group such as the factors fluorine, chlorine, bromine and iodine. The lifestyles and efficiency of an normal incandescent lamp are suffering from the gradual evaporation of tungsten and also its working temperature. The addition of a small amount of any halogen vapour to the argon gas submitting of a lamp has the effect that under sure conditions the metallic evaporated from the tungsten filament on attaining the extraordinarily low temperature close to the wall of the envelope forms a compound of tungsten halogen and being very voltage tungsten halogen suffers from thermal diffusion in the route of filament and on attaining the filament at high temperature it decomposes into the tungsten and halogen. In this manner the evaporated tungsten is lower back lower back and restored to the filament by a chemical reaction. Halogen therefore works as a shipping gasoline. This regenerative cycle maintains the interior of the bulb in a clean situation with out depositing any metal vapor on the wall. The motion requires a better bulb temperature of about 250? that can be withstood through the glass. Therefore a incredibly costly material great is selected because the envelope material and its size is stored very small wherein excessive fuel filling strain in made feasible. This gives lengthy existence of approximately 2000 hours to the lamp with higher mild output of about 22-23 lumens/watt.

Halogen lamps are made within the standard wattage of 300 W, 500 W, 600 W, 1000 W, 1500 W & 2000 W however now and again these are made upto five kW. These lamps are appropriate for outdoor illumination of buildings, sports grounds, parks, air ports, fountains etc. And extensively utilized in public halls, sports halls, factories, photo movie, T.V. Studios, overhead projectors, vehicle lighting, signaling and many others.

ELECTRONICS & INSTRUMENTATION Engineering Interview Questions
Question 28. What Is An Electric Lamp?

Answer :

An electric powered lamp is a tumbler bulb, often filled with nitrogen or some different chemically inactive gasoline containing a wire or filament commonly manufactured from tungsten in which the passage of an electric powered cutting-edge via the filament heats it to a white warmness and then to the seen radiation i.E. Light.

Question 29. What Are The Types Of Lamps?

Answer :

There are forms of lamps for producing light via strength.

Incandescent lamp
Electric arc lamp and
Gas discharge lamp.
Question 30. What Do You Mean By Incandescent Lamp?

Answer :

The incandescent or filament kind includes a document metallic wire of excessive resistance known as filament enclosed in an evacuated glass globe. When the electrical modern passes thru the filament, warmth is produced and the temperature of the filament increases. At excessive temperature, it radiates heat as well as mild energy thereby generating electric lighting fixtures via incandescence of a heated filament.

Question 31. What Are The Types Of Incandescent Lamps?

Answer :

The two varieties of incandescent lamps are:-

Metal filament lamps &
Carbon filament lamps.
Question 32. What Should Be The Properties Of Metal As A Filament In The Incandescent Lamp?

Answer :

It need to have high melting factor, low vapour pressure, high resistivity and coffee-temperature coefficient. It ought to be ductile and automatically very strong to resist vibrations at some point of everyday use.

Question 33. Which Materials Are Used For The Filament Of The Incandescent Lamps?

Answer :

Tungsten, Tantalum and Carbon.

Electrician Assistant Interview Questions
Question 34. Which Material Is Mostly Used For The Filament Of Incandescent Lamps And Why?

Answer :

Tungsten is widely used for the filament of the incandescent lamp because of its high-temperature co-green, excessive melting point, low vapour stress, ductility and suitable mechanical electricity.

Question 35. What Are The Melting Point And Working Temperature Of The Tungsten Filament?

Answer :

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

Question 36. What Are The Types Of Filaments Normally Used?

Answer :

Straight cord kind
Coiled kind and
Coiled-coil kind.
Electrician Interview Questions
Question 37. Why Are The Modern Incandescent Lamps Made Of Coiled Filament?

Answer :

The causes are as follows:-

Coiled coil filament is automatically stronger.
It can operate at excessive temperature.
It offers more output.
It gives more efficiency.
Question 38. On Which Principle Does The Incandescent Lamp Work?

Answer :

Incandescent lamp works via the heating impact of electricity.

Question 39. What Is Specular Reflection?

Answer :

Specular reflection approach the reflection on a few in the form of a beam of mild but no longer scattered. In this mirrored image except the eye is positioned in the route of the pondered beam the viewer is blind to the life of mild.

Diffuse reflection manner the mirrored image of mild energy within the scattered shape in all route. In this reflection the viewer can see the illuminated floor but not the mild supply.

Question 40. What Is Glare?

Answer :

Glare way the brightness inside the area of imaginative and prescient of this kind of man or woman as to reason annoyance, pain, interference with imaginative and prescient or eye fatigue.

Electrical Power System Interview Questions
Question forty one. What Is Polar Curve Of A Lamp?

Answer :

A polar curve is a handy manner of showing how the candle strength of a lamp varies in exceptional instructions. Polar curves are used to decide the M.H.C.P.,M.S.C.P. And the real illumination of a surface with the aid of using the candle energy in the particular path.

Question 42. Why Does Uniformly Distributed Light Not Come From Any Practical Type Of Lamp?

Answer :

Due to its unsymmetrical form.

Electrical Drives Interview Questions
Question forty three. How Are Hard And Long Shadows Avoided?

Answer :

Hard and lengthy shadows are averted with the aid of

Using massive numbers of small luminaires mounted over a minimal height of two.5 metres.
Using wide floor assets of light with the aid of using diffusing globe over filament lamp or with the aid of the use of indirect lights device.
Question forty four. What Do You Mean By Brightness And Its Unit?

Answer :

The flux emitted according to unit place of the source in a course at right angles to the floor is known as brightness. Its unit is candles / m2 or candles / ?cm?2 or candles / ?feet?2.

Question forty five. What Is Depreciation Factor?

Answer :

It is the ratio of illumination beneath ordinary condition of vintage installation to the illumination below best situation of recent installation.

Question forty six. What Are The Laws Of Illumination?

Answer :

Illumination is directly proportional to the luminous intensity of the source.
Inverse square law – The illumination of a surface receiving its flux from a factor source is inversely proportional to the rectangular of the distance between the floor and the source.
Lambert’s cosine regulation – The illumination of a surface at any point is proportional to the cosine of the angle among the everyday on the point and the route of the luminous flux.
Question 47. What Are The Characteristics Of Good Illumination?

Answer :

The light need to no longer strike directly the eyes.
The type and size of the lamp should be accurate.
Proper region must be made.
Reflecting gadget ought to be appropriate for cause.
Hard and long shadows should be avoided.
Question 48. What Are The Factors Which Affect The Correct Illumination?

Answer :

Nature of the work
Architectural layout
Surroundings
Nature of light and 
Maintenance.
Question 49. What Are The Factors To Be Considered In The Design Of A Lighting Scheme?

Answer :

The factors are as follows: 

 Illumination level
Glare
Shadow
Space top ratio
Mounting height of the lamp
Area to be illuminated
Colour of surrounding partitions
Movement of the item
Utilization factor and 
Depreciation factor.
Question 50. What Are The Advantages Of Correct Illumination?

Answer :

Production thing increases
Accident decreases
Wastage of products decreases.
Question fifty one. What Do You Mean By Direct Lighting?

Answer :

In this lighting fixtures scheme the light does not reach the surface without delay from the source, maximum light is thrown upwards to the ceiling from which it's miles disbursed all around the room through diffuse reflectance. The glare being reduced the ensuing illumination becomes softer. It is used for decoration purposes in cinemas, theaters, and lodges and many others. And in workshops wherein large machines and different obstructions could cause difficult shadows if direct lights is employed.

Question fifty two. What Do You Mean By Semi-direct Lighting?

Answer :

In this lighting scheme the full mild flux is made to fall downwards without delay with the assist of semi-direct reflector on the running floor and also to illuminate the ceilings and walls. It is best acceptable to rooms with excessive ceilings wherein a high stage of uniformly distributed illumination is suitable.

Question fifty three. What Do You Mean Semi-indirect Lighting?

Answer :

In this lighting scheme the light comes partly from the ceiling by using diffused reflection and party direct from the supply at the working surface. As it is glare free with tender shadows it's miles mainly used for indoor mild decoration functions.

Question 54. What Do You Mean By General Lighting?

Answer :

In this lighting scheme lamps product of diffusing glass are hired which give almost identical distribution of mild in all course.

Question fifty five. What Do You Mean By Local Lighting?

Answer :

Local lighting fixtures method an severe illumination on some specific points through adjustable fittings. In this lighting fixtures scheme lamps are set up in deep reflectors to avoid glare.

Question 56. What Do You Mean By Specular Reflection And Diffuse Reflection?

Answer :

Specular reflection method the mirrored image on a few inside the form of a beam of mild but not scattered. In this reflection, until the eye is placed inside the course of the meditated beam the viewer is ignorant of the life of light.

Diffuse mirrored image means the mirrored image of light strength in the scattered shape in all course. In this mirrored image, the viewer can see the illuminated surface however no longer the light supply.

Question 57. What Is Light?

Answer :

Light is a form of strength, that's radiated by way of heated our bodies. The mild is the part of the radiant electricity which produces a sensation (of light) on the human eye.

Question 58. What Is Luminous Flux?

Answer :

Luminous flux is the light strength radiated in line with 2d from a luminous body in the form of mild waves. It is measured in lumen.

Question 59. What Is Lumen?

Answer :

Lumen is the unit of luminous flux that is identical to the flux emitted consistent with unit solid perspective from a uniform source of 1 candle energy.

1 lumen = 0.0016 watt (approx).

Question 60. What Is Luminous Intensity?

Answer :

Luminous flux emitted with the aid of the assets in keeping with unit solid attitude in any precise path is called the luminous intensity.

Question sixty one. What Is Illumination?

Answer :

The luminous flux falling according to unit location on a surface is called illumination and is expressed in Lumen/m2.

Question sixty two. What Is A Standard Candle?

Answer :

A standard candle is that weighs 1/6 pound of natural spermaceti wax and burning at the charge of a hundred and twenty grains per hour i.E. 7.776 grams per hour.

Question sixty three. What Is A Standard Candle Power?

Answer :

The mild popping out from a preferred candle used because the unit of illuminating strength of a lighting fixtures source is known as preferred candle strength.

Question 64. What Are Foot-candle And Metre-candle?

Answer :

Foot candle or Lumen in step with square foot is described as the illumination produced on the inner floor of a hollow sphere of a hollow sphere of radius one foot through a factor floor at the center of intensity of one candela.

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

Question 65. What Will Be The Total Flux Emitted By A Source Of 60 Candle Power?

Answer :

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

Question sixty six. What Do You Mean By M.H.C.P?

Answer :

Mean Horizontal Candle Power (M.H.C.P) is the imply of the candle powers in all instructions within the horizontal aircraft passing through the supply of mild.




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