Light Level or Illuminance, is the total luminous flux incident on a surface, per unit area. The work plane is where the most important tasks in the room or space are performed.
Measuring Units Light Level - Illuminance
Illumenance is measured in foot candles (ftcd, fc, fcd) (or lux in the metric SI system). A foot candle is actually one lumen of light density per square foot, one lux is one lumen per square meter.
•1 lux = 1 lumen / sq meter = 0.0001 phot = 0.0929 foot candle (ftcd, fcd)
•1 phot = 1 lumen / sq centimeter = 10000 lumens / sq meter = 10000 lux
•1 foot candle (ftcd, fcd) = 1 lumen / sq ft = 10.752 lux
Common Light Levels Outdoor
Common light levels outdoor at day and night can be found in the table below:
Condition Illumination
Sunlight : 107,527 Lux
Full Daylight :10,752 Lux
Overcast Day : 1,075 Lux
Very Dark Day : 107 Lux
Twilight : 10.8 Lux
Deep Twilight : 1.08 Lux
Full Moon : 0.108 Lux
Quarter Moon : 0.0108 Lux
Starlight : 0.0011 Lux
Overcast Night : 0.0001 Lux
Common and Recommended Light Levels Indoor
The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the area closest to windows, the light level may be reduced to approximately 1,000 lux. In the middle area its may be as low as 25 - 50 lux. Additional lighting equipment is often necessary to compensate the low levels.
Earlier it was common with light levels in the range 100 - 300 lux for normal activities. Today the light level is more common in the range 500 - 1000 lux - depending on activity. For precision and detailed works, the light level may even approach 1500 - 2000 lux.
The table below is a guidance for recommended light level in different work spaces:
Activity Illumination
Public areas with dark surroundings :20-50 Lux
Simple orientation for short visits 50 - 100 Lux
Working areas where visual tasks are only occasionally performed : 100 - 150 Lux
Warehouses, Homes, Theaters, Archives : 150 Lux
Easy Office Work, Classes : 250 Lux
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories : 500 Lux
Supermarkets, Mechanical Workshops, Office Landscapes : 750 Lux
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres : 1,000 Lux
Detailed Drawing Work, Very Detailed Mechanical Works : 1500 - 2000 Lux
Performance of visual tasks of low contrast and very small size for prolonged periods of time Lux 2000 - 5000 Lux
Performance of very prolonged and exacting visual tasks : 5000 - 10000 Lux
Performance of very special visual tasks of extremely low contrast and small size
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