Illuminance - Recommended Light Levels

Recommended light levels - illuminance - for some types of working activities

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:

ConditionIllumination
(ftcd)(lux)
Sunlight 10000 107527
Full Daylight 1000 10752
Overcast Day 100 1075
Very Dark Day 10 107
Twilight 1 10.8
Deep Twilight 0.1 1.08
Full Moon 0.01 0.108
Quarter Moon 0.001 0.0108
Starlight 0.0001 0.0011
Overcast Night 0.00001 0.0001

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:

ActivityIllumination
(lux, lumen/m2)
Public areas with dark surroundings 20 - 50
Simple orientation for short visits 50 - 100
Working areas where visual tasks are only occasionally performed 100 - 150
Warehouses, Homes, Theaters, Archives 150
Easy Office Work, Classes 250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories 500
Supermarkets, Mechanical Workshops, Office Landscapes 750
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theaters 1,000
Detailed Drawing Work, Very Detailed Mechanical Works 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

Calculating Illumination

Illumination can be calculated as

I = Ll Cu LLF / Al       (1)

where

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

Related Topics

  • Physiology - Human physiology, air quality and comfort temperatures, activity and metabolic rates, health effects of carbon monoxide and more

Related Documents

Tag Search

  • en: illuminance light level office rooms production activity
  • es: iluminancia actividad productiva salas de oficina nivel de luz
  • de: Beleuchtungslichtpegel Büroräume Produktionstätigkeit

Search the Engineering ToolBox

- "Search is the most efficient way to navigate the Engineering ToolBox!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!

close