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Task Illuminance

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This procedure is the currently recognized method of the Illuminating Engineering Society of North America to determine the level of maintained illumination needed to perform a specific task. This method considers factors that most commonly contribute to the visual comfort of the various task listed later in this article. It provides a range of illumination levels for defined task, then specifies a target luminance level from within that range using factors determined through research of lighting performance requirements.

 

The following conditions are factored into this method:

  • Task to be performed.
  • Detail of the objects to be viewed.
  • Age of the observer.
  • Importance of speed and accuracy for the visual task
  • Reflectance of the background material. 
     

Determining Appropriate Illuminance Levels

Step 1 Determine the type of activity for which the level of lighting is to be selected.

Step 2 Select the appropriate illuminance category by one of the following methods.

 

When the visual task is defined by one of the typical task categories, choose the appropriate illuminance category from Table A

 

Specific Task Illuminance Level Guide - Table A

Type of Activity Illuminance Category or fc Level Type of Activity Illuminance Category or fc Level Type of Activity Illuminance Category or fc Level
Auditoriums Banks Merchandising Spaces
Assembly C Lobby-General C Circulation 30
Social Activity C Writing Area D High Activity 30
Aircraft Maintenace Teller's Stations E Medium Activity 20
General 75 Breweries D Low Activity 10
Electrical, Auto 150 Canning and Preserving Merchandising
Upholstry 100 Continuous-Belt Sanding E High Activity 115
Parts Inspection 100 Sink Canning E Medium Activity 100
Paint Shop 100 Hand Packing D Low Activity 30
Aircraft Manufacturing Inspection F Offices
Rough Bench Work 50 Clothing Products (see reading) C
Drilling, riveting, screw 75 Cutting and Sewing G Lobbies, Lounges C
Medium Bench Work 100 Pressing F Reception Areas C
Final Assembly 100 Conference Rooms Reading
Assembly Conferring D Xerography, mimeograph D
Simple D Corridors D Computer Screens D
Moderately Difficult E Corridors B #3 pencil and hard leads E
Difficult G Drafting #4 pencil and hard leads F
Very Difficult G Muylar, vellum or tracing E Ball-point pen D
Audiovisual Areas D Low Contrast F 8 and 10 point type D
Automobile Manufacturing Blueprints E Glossy Magazines D
Frame Assembly 50 Exhibition Halls C Newsprint D
Chassis Assembly 100 Libraries Schools
Final Assembly 200 Reading Areas D Classrooms E
Bakeries D   Sci. Laboratories E
  Stairwells C

 

If a specific task cannot be established, the illuminance category may be determined from the generic task description listed in Table B.

Range of Illuminances - Table B

Type of Activity Illuminance Category Lux Foot-candles Reference Work Plane
Public spaces with dark surroundings A 20-30-50 2-3-5  
Simple orientation for short temporary visits B 50-75-100 5-7.5-10 General Lighting throughout spaces
Working spaces where visual tasks are only occasionally performed C 100-100-100 10-15-20  
Performance of visual task of high contrast or large size D 200-300-500 20-35-50  
Performance of visual task of medium contrast or small size E 500-750-1000 50-75-100 Illuminance on task
Performance of visual task of low contrast or very small size over F 1000-1500-2000 100-150-200  
Performance of visual task of low contrast or very small size over a prolonged period G 2000-3000-5000 200-300-500 Illuminance on task obtained by a combination of general and task lighting

 

Step 3 Establish illuminance target value. Once the illuminance category is chosen, an exact illuminance level may be determined from within this range. These levels are established on Table C by matching the appropriate user, room, and task characteristics with the previously determined illuminance category.

 

Illuminance Values - Table C (General Light)

Factors Illuminance Categories
Average Age of Occupants Average Reflectance of Room Surface A B C
Under 40 Over 70 2 5 10
30-70 2 5 10
Under 30 2 5 10
40-55 0ver 70 2 5 10
30-70 3 7 15
Under 30 5 10 20
Over 55 Over 70 3 7 15
30-70 5 10 20
Under 30 5 10 20

 

Illuminance Values - Table C (Illuminance on Task)

Factors Illuminance Categories
Average Age of Occupants Demand for speed and/or accuracy Average Reflectance of Room Surface D E F G
Under 40 Not Important Over 70 20 50 100 200
30-70 20 50 100 200
Under 30 30 75 150 300
Important 0ver 70 20 50 100 200
30-70 30 75 150 300
Under 30 30  75 150 300
Critical Over 70 30 75 150 300
30-70 30 75 150 300
Under 30 30 75 150 300
40-55 Not Important Over 70 20 50 100 200
30-70 30 75 150 300
Under 30 30 75 150 300
Important 0ver 70 30 75 150 300
30-70 30 75 150 300
Under 30 30 75 150 300
Critical Over 70 30 75 150 300
30-70 30 75 150 300
Under 30 50 100 200 500
Over 55 Not Important Over 70 30 75 150 300
30-70 30 75 150 300
Under 30 30 75 150 300
Important 0ver 70 30 75 150 300
30-70 30 75 150 300
Under 30 50 100 200 500
Critical Over 70 30 75 150 300
30-70 50 150 200 500
Under 30 50 100 200 500