Luminance vs Illuminance
Luminance and illuminance are two very important concepts discussed in physics. Luminance is the amount of light energy that is produced by a surface or an object. Illuminance is the amount of light energy incident on a given surface. The concepts of luminance and illuminance are widely used in fields such as physics, photography, chemistry, engineering, astronomy, astrophysics and numerous other fields. In this article, we are going to discuss what luminance and illuminance are, the definitions of luminance and illuminance, the units of measurement used in measuring luminance and illuminance, their applications, and finally the comparison of luminance and illuminance. The differences between luminance and illuminance are summarized at the end.
What is Luminance?
Luminance is a concept that is widely used in physics. Luminance is the amount of light detected by a typical human eye emitted from a flat surface. Luminance is the luminous intensity per unit area of light travelling in a given direction. The luminance measures how much luminous power will be detected by an average human eye from a particular angle.
The SI unit for measuring luminance is candela per square meter, which is denoted as cd / m2. The CGS unit for measuring luminance is known as stilb which is equal to candela per square centimeter. The SI unit is also equal to one “nit”.
Luminance is a very important property in photography as it describes the amount of light that will be used in the photograph formation. The input luminance of an ideal optical system is equal to the output luminance of the system. In a practical situation, the output luminance is always smaller than the input luminance. The image cannot be more bright than the source itself.
Luminance is often mistaken for luminosity and illuminance due to the similarity of the words, but these three are totally different from each other.
What is Illuminance?
Illuminance is a term which is often misinterpreted as luminance or luminosity. Illuminance measures the amount of light incident on a surface. In other words, illuminance measures the amount of light illuminating the surface. This is weighted by the wavelength, to compensate for the sensitivity of the human eye. Illuminance is defined as the total luminance flux incident on a given surface per unit area.
Illuminance is measured in either lux or lumens per square meter. The SI unit of illuminance is cd.sr.m-2.
Illuminance is widely used in photography to measure the light illuminating the surface being photographed. Too much illuminance will wash out all the details from a surface while too little illuminance will be hard to detect.
What is the difference between luminance and Illuminance?
• Luminance is a quantity which identifies the amount of light emitted from a surface whereas illuminance is a quantity which identifies the light illuminating the surface.
• Luminance depends on the nature and properties of the surface whereas illuminance of a surface does not depend on the nature of the surface.