Planar Illuminance
This page describes how Planar Illuminance is calculated and integrated to the sensor (horizontally or vertically).
Planar Illuminance Overview
The illuminance on a point is calculated by the cosine on the angle of incidence ε. The formula is .
Types of Integration Direction of Planar Illuminance
On the following examples, the source is simulated by a local point source.
The pixel is only sensitive on one side. Its sensitivity is lambertian.
Horizontal plan
The horizontal illuminance is the most common way to calculate illuminance.
- The integration direction is perpendicular to the horizontal plan and the surface sensor.
- The normal illuminance follows the Bouguer law.
- The formula is
Vertical plan
When the surface sensor is applied vertically, the lateral orientation becomes an important parameter to determinate the illuminance.
The integration direction is perpendicular to the vertical plan and parallel to the surface sensor (that is, a wall on the road).
The formula is
General case
In the general case, you must define the integration direction.
The same integration direction is applied on each pixel of the sensor.
On the figure below, the integration direction is perpendicular to the blue mechanical plans.