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Understanding Lux and Illuminance: A Guide to Light Levels

lux illuminance light measurement lighting lumens

This article explores the concept of lux, also known as illuminance, and provides charts outlining recommended light levels for various indoor and outdoor environments. Illuminance refers to the amount of light falling on a surface, and it’s a crucial factor in creating comfortable and functional spaces.

What is Illuminance?

Illuminance, or light level, measures the total luminous flux (light) incident on a surface per unit area. Think of it as how much light is actually hitting a particular spot. It’s commonly measured in:

  • Lux (lx): The standard unit in the International System of Units (SI).
  • Footcandles (fc, ftcd, fcd): Often used in the United States.

Here’s how these units relate to each other:

  • 1 Lux = 1 Lumen/meter²
  • 1 Footcandle = 1 Lumen/sq. ft = 10.752 Lux
  • 1 Lux = 0.0001 Phot = 0.0929 Footcandle
  • 1 Phot = 1 Lumen/sq. cm = 10,000 Lux

Light Levels from Natural Sources

The following table illustrates the illuminance levels provided by different natural light sources:

Natural SourceIllumination (ftcd)Illumination (lux)
Sunlight10,000107,527
Full Daylight1,00010,752
Overcast Day1001,075
Very Dark Day10107
Twilight110.8
Deep Twilight0.11.08
Full Moon0.010.108
Quarter Moon0.0010.0108
Starlight0.00010.0011
Overcast Night0.000010.0001

This chart provides recommended illuminance levels for various indoor environments:

Light Levels IndoorsIllumination (Lux, Lumen/sq.m )
Public areas with dark surroundings20 to 50
Warehouses, Homes, Theaters150
Easy Office Work, Classes250
Normal office work, PC work, Study library, Groceries, Labs, Show rooms500
Super markets750
Mechanical workshops, normal drawing work1000
Detailed drawing work1500 to 2000
Visual tasks with low contrast & very small size for prolonged periods of time2000 to 5000
Training rooms500
Auditoria150 to 200
Child care centers, Parking , entrances, physical fitness space500

The following image displays recommendations for light levels on roadways and sidewalks:

outdoor light levels

Conclusion

Lux and illuminance are crucial in determining the appropriate lighting levels for different spaces. While illuminance refers to the amount of light falling on a surface (measured in lux), different applications require specific lux levels for optimal visibility and comfort. For example, office spaces typically require 300 to 500 lux, while outdoor stadiums may need over 1000 lux. Understanding these values helps in selecting proper lighting solutions, improving energy efficiency, and ensuring safety in both residential and commercial settings.