Is there a difference between “illuminance” and “luminance”?
Lighting terms can be confusing; two of the most used and often mixed up terms are illuminance and luminance.
Illuminance is the lighting up of a surface area. It is a measure of the amount of light falling onto (illuminating) and spreading over the given surface area. It correlates with how humans perceive brightness of an illuminated area. Illuminance is often called brightness, which leads to confusion, as brightness can be used to describe luminance also. Brightness is a reference to physiological sensations and perceptions of light; it is not to be used for quantitative purposes.
The SI unit for illuminance is lux (lx). Sometimes people use the term foot-candle; foot-candle is a non SI unit of illuminance widely used in the United States. The term “foot-candle” means “the illuminance on a surface by a candela source one foot away”. One foot-candle is equivalent to one lumen per square foot which is approximately 10.764 lux.
Luminance is the measure of the amount of light passing through, emitting or reflected from a particular surface traveling at a solid angle; it indicates how much luminous power can be perceived by a human eye. Thus luminance indicates the brightness of emitted or reflected surface. Luminance is used in the display industry to quantify the brightness of displays.
The SI unit for luminance is candela/square meter (cd/m²). There are also a variety of units used for luminance, one of the common unit used mainly in the United States is foot-lambert (fL); 1 foot-lambert (fL) equals 1/π candela/square foot, or 3.426 cd/m². People in the industry will be familiar with the term nit (nt), nit is a non SI term used for luminance, and 1 nit is equivalent to 1 cd/m².
About the Author: Garie Xu
Garie Xu is the Sales Engineer of Konica Minolta Sensing Singapore Pte Ltd. Graduated from a manufacturing engineering background, he is mainly involved in sales, seminar, training and coaching in the field of light and color management. With his prior 3 years’ experience in the oil and gas industry and 2 years in Konica Minolta, he is providing solutions to the many industrial applications. He has also conducted seminars and workshops to educate the industry on instrumentation technologies and color science.