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A useful article with detail data about the Illumination standard

Edit: East Bright Technology Limited    Date: Jul 21, 2016

Light Level or Illuminance is the total luminous flux incident on a surface per unit area. The area - the work plane - is where the most important tasks in the room or space are performed.

Measuring Units Light Level - Illuminance

Illuminance is measured in foot candles (ftcd, fc, fcd) in the Imperial system or lux in the metric SI system.

•one foot candle = one lumen of light density per square foot

•one lux = 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

Outdoor Light Levels

Common outdoor light levels at day and night:

Indoor Light Levels

The outdoor light level is approximately 10000 lux on a clear day. In a building in the area closest to the windows the light level may be reduced to approximately 1000 lux. In the middle area it may be as low as 25 - 50 lux. Additional lighting is often necessary to compensate 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.

Recommended light levels for different work spaces:

Calculating Illumination

Illumination can be calculated as

I = Ll Cu LLF / Al       (1)


I = illumination (lux, lumen/m2)

Ll = luminance per lamp (lumen)

Cu = coefficient of utilization

LLF = light loss factor

Al = area per lamp (m2)

Example - Illumination

10 incandescent lamps of 500 W (10600 lumens per lamp) are used in an area of 50 m2. With Cu 

= 0.6 and LLF = 0.8 illumination can be calculated as

I = 10 (10600 lumens) (0.6) (0.8) / (50 m2)

  = 1018 lux

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