SOME IMPORTANT QUESTION OF ILLUMINATION

 Question 1. What are the characteristics of good illumination? 

Answer : 

• 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. 

Question 2. What are the factors which affect the correct illumination? 

Answer : 

• Nature of the work 
• Architectural design 
• Surroundings 
• Nature of light and 
• Maintenance. 

Question 3. 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 height ratio 
• Mounting height of the lamp 
• Area to be illuminated 
• Colour of surrounding walls 
• Movement of the object 
• Utilization factor and 
• Depreciation factor. 

Question 4. What do you mean by direct lighting? 

Answer : 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. 

Question 5. What do you mean by semi-direct lighting? 

Answer :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. 

Question 6. What do you mean semi-indirect lighting? 

Answer : 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. 

Question 7. What is Light? 

Answer : 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. 

Question 8. What is Luminous Flux? 

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

Question 9. What is Lumen? 

Answer : 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). 

Question 10. What is Luminous Intensity? 

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

Question 11. What are Foot-candle and Meter-candle? 

Answer : 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. 

Question 12. What do you mean by M.H.C.P? 

Answer : 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. 

Question 13. What is Depreciation Factor? 

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

Question 14. 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 point source is inversely proportional to the square of the distance between the surface and the source. 
• 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. 

Question 15. What do you mean by brightness and its unit? 

Answer : 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 / cm2 or candles / ft 2. 

Question 16. What is Glare? 

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

Question 17. 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 due to its high-temperature co-efficient, high melting point, low vapor pressure, ductility and good mechanical strength.