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Which of the following are the essentials of any good lighting system? (a) Adequate illumination of suitable color on the working surfaces. (b) Avoidance of hard shadows (c) Avoidance of glare (d) Maintenance free

Which of the following are the essentials of any good lighting system? (a) Adequate illumination of suitable color on the working surfaces. (b) Avoidance of hard shadows (c) Avoidance of glare (d) Maintenance free Correct Answer (a), (b), (c) and (d)

Essentials requirements/criteria of good lightening system:

  • Proper light intensity
  • Uniformity of light i.e. light should not fluctuate
  • Dazzle capability and luminance distribution
  • Light pulsation and color rendering
  • Shading of light
  • No dark shadows should form
  • Least maintenance required

Important Points

Levels of illumination required for various tasks:

                                      Activity

                                Illuminance
                              (lux, lumen/m2)

Public areas with dark surroundings

20 - 50

Simple orientation for short visits

50 - 100

Areas with traffic and corridors - stairways, escalators and travelators - lifts - storage spaces

100

Working areas where visual tasks are only occasionally performed

100 - 150

Warehouses, homes, theaters, archives, loading bays

150

Coffee break room, technical facilities, ball-mill areas, pulp plants, waiting rooms, 

200

Easy office work

250

Class rooms

300

Normal office work, PC work, study library, groceries, show rooms, laboratories, check-out areas, kitchens, auditoriums

500

Supermarkets, mechanical workshops, office landscapes

750

Normal drawing work, detailed mechanical workshops, operation theaters

1000

Detailed drawing work, very detailed mechanical works, electronic workshops, testing and adjustments

1500 - 2000

Performance of visual tasks of low contrast  and very small size for prolonged periods of time

2000 - 5000

Performance of very prolonged and exacting visual tasks 

5000 - 10000

Performance of very special visual tasks of extremely low contrast and small size

10000 - 20000

 

Units and various terms of illumination:

  • Luminous flux: Luminous energy emitted per unit of time by a light source. Unit: lumen (lm).
  • Luminous intensity: Luminous flux emitted in a given direction by a light that is not equally distributed. Unit: candela (cd).
  • Illumination: Level of illumination of a surface of one square meter when it receives a luminous flux of one lumen. Unit: lux = lm/m2.
  • Luminance or photometric brilliance: The relation between luminous intensity and the surface seen by an observer situated in the same direction. Unit: cd/m2.
  • Contrast: Difference in luminance between an object and its surroundings or between different parts of an object.
  • Reflectance: Proportion of light that is reflected by a surface. It is a non-dimensional quantity. Its value ranges between 0 and 1.

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