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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:
- Fundamental quantity: the other radiometric quantities are derived
from it.
- Invariant along a ray: stays constant along a ray. Thus, radiance
is associated with rays in a ray tracer.
- 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

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