06-05-2019, 10:42 AM
Laws of Illumination
The Inverse Square Law of Illuminance
The Inverse Square Law of Illuminance is a fundamental principle in lighting design and engineering that describes the relationship between the distance of a light source and the level of illuminance (light intensity) on a surface.
The law states that the intensity of light on a surface decreases as the distance between the surface and the light source increases, and this decrease is proportional to the square of the distance between them.
Illuminance (E) at any point on a plane perpendicular to the line joining the point and source is inversely proportional to the square of the distance between the source and plane.
![[Image: image-20.png]](http://frontdesk.co.in/wp-content/uploads/2019/06/image-20.png)
E = I / d2
I = intensity
d = Distance
Where I is the illuminance on the surface in lux (lx), E is the luminous flux emitted by the light source in lumens (lm), and d is the distance between the light source and the surface in meters (m).
This means that if the distance between the light source and the surface is doubled, the illuminance will decrease to one-quarter of its original value. Similarly, if the distance is tripled, the illuminance will decrease to one-ninth of its original value.
The Inverse Square Law of Illuminance is important to consider when designing lighting systems, as it can have a significant impact on the level of illumination achieved in a space. It is also important to note that this law assumes that the light source is a point source, and for sources that are not point sources, other factors may need to be taken into account
for more detail read ... The Inverse Square Law Of Illuminance
The Cosine Law of Illuminance / Lambert’s Cosine Law
The Cosine Law of Illuminance is fundamental principle in lighting design and engineering that describes the relationship between the angle of incidence of light and the level of illuminance on a surface.
The law states that the illuminance on a surface is proportional to the cosine of the angle of incidence of the light on the surface.
Illuminance at a point on a plane is proportional to the cosine of the angle of light incident (the angle between the direction of the incident light and the normal to the plane).
Eθ = E cosθ
Where E is the illuminance on the surface in lux (lx), E0 is the illuminance on a surface that is perpendicular to the incident light, and θ is the angle of incidence between the light and the surface.
![[Image: image-21.png]](http://frontdesk.co.in/wp-content/uploads/2019/06/image-21.png)
![[Image: image-22.png]](http://frontdesk.co.in/wp-content/uploads/2019/06/image-22.png)
This means that as the angle of incidence between the light and the surface increases, the illuminance on the surface decreases. At an angle of 90 degrees, the cosine of the angle is zero, and the illuminance on the surface is also zero.
The Cosine Law of Illuminance is important to consider when designing lighting systems, as it can have a significant impact on the level of illumination achieved in a space, particularly in applications where light is directed at an angle to the surface, such as in outdoor lighting or in the lighting of artwork or displays.
It should be noted that the Cosine Law of Illuminance assumes that the surface being illuminated is flat and perpendicular to the incident light, and for surfaces that are not flat or perpendicular, other factors may need to be taken into account.
for more detail ...
The Cosine Law of Illuminance
To know more about illumination read....Illumination in architecture
The Inverse Square Law of Illuminance
The Inverse Square Law of Illuminance is a fundamental principle in lighting design and engineering that describes the relationship between the distance of a light source and the level of illuminance (light intensity) on a surface.
The law states that the intensity of light on a surface decreases as the distance between the surface and the light source increases, and this decrease is proportional to the square of the distance between them.
Illuminance (E) at any point on a plane perpendicular to the line joining the point and source is inversely proportional to the square of the distance between the source and plane.
E = I / d2
I = intensity
d = Distance
Where I is the illuminance on the surface in lux (lx), E is the luminous flux emitted by the light source in lumens (lm), and d is the distance between the light source and the surface in meters (m).
This means that if the distance between the light source and the surface is doubled, the illuminance will decrease to one-quarter of its original value. Similarly, if the distance is tripled, the illuminance will decrease to one-ninth of its original value.
The Inverse Square Law of Illuminance is important to consider when designing lighting systems, as it can have a significant impact on the level of illumination achieved in a space. It is also important to note that this law assumes that the light source is a point source, and for sources that are not point sources, other factors may need to be taken into account
for more detail read ... The Inverse Square Law Of Illuminance
The Cosine Law of Illuminance / Lambert’s Cosine Law
The Cosine Law of Illuminance is fundamental principle in lighting design and engineering that describes the relationship between the angle of incidence of light and the level of illuminance on a surface.
The law states that the illuminance on a surface is proportional to the cosine of the angle of incidence of the light on the surface.
Illuminance at a point on a plane is proportional to the cosine of the angle of light incident (the angle between the direction of the incident light and the normal to the plane).
Eθ = E cosθ
Where E is the illuminance on the surface in lux (lx), E0 is the illuminance on a surface that is perpendicular to the incident light, and θ is the angle of incidence between the light and the surface.
This means that as the angle of incidence between the light and the surface increases, the illuminance on the surface decreases. At an angle of 90 degrees, the cosine of the angle is zero, and the illuminance on the surface is also zero.
The Cosine Law of Illuminance is important to consider when designing lighting systems, as it can have a significant impact on the level of illumination achieved in a space, particularly in applications where light is directed at an angle to the surface, such as in outdoor lighting or in the lighting of artwork or displays.
It should be noted that the Cosine Law of Illuminance assumes that the surface being illuminated is flat and perpendicular to the incident light, and for surfaces that are not flat or perpendicular, other factors may need to be taken into account.
for more detail ...
The Cosine Law of Illuminance
To know more about illumination read....Illumination in architecture