Malin's Magnificent Math
Home

Colour: Physics & Light

Reflection Functions

Illumination Models

Ray Tracing

Radiometry

What is radiometry?

Radiometry is the science of light (electromagnetic) energy measurement.

Calculating angles and solid angles:

               

    The circle has 2π radians. The sphere has 4π steradians.

Differential Solid Angles


      

Projected Solid Angle:

           

Projection of the differential area (on the sphere's surface) onto the base of the sphere.

      

What is radiance?

Radiance (or luminance) is the power per unit area per unit solid angle.

      

Symbol:

      

Flux: Radiant Power

      

Radiant Properties:

  1. Fundamental quantity: the other radiometric quantities are derived from it.
  2. Invariant along a ray: stays constant along a ray. Thus, radiance is associated with rays in a ray tracer.
  3. The response of a sensor is proportional to surface radiance. Thus, a wall is equally bright across a range of viewing distances.

What is Irradiance?

Irradiance (illuminace) is the power per unit area incident on a surface.

      

      

What is Radiosity?

Radiosity (luminosity) is the power per unit area leaving a surface.

      

      

What is Radiant Intensity?

Radiant intensity is the radiant power per solid angle of a point source.

           

Irradiance: Distance Source

      

Irradiance: Point Source