There are cases where a simulation of an illumination system does not match the experimental results due to the lack of a comprehensive light source model. For light sources that are closer to the optics, the light is collected over a larger solid angle with the possibility of surface distribution as well. In this case, a complete model of the light source with reflections and refractions from the physical size of the light source may be more appropriate to achieve results that match real life.
A simple case for the directional distribution can be approximated to be isotropic or Lambertian distribution. 
Below are a few representative light sources that we use in illumination design.
- LEDs (light emitting diodes), single chip and phosphorus models
- LDs (laser diodes)
- Incandescent light sources such as light bulbs and the sun
- Fluorescent light sources such as fluorescnet lamps
- Metal vapour light sources such as metal-halide lamps
- High-pressure gas discharge sources
There are four ways to create a complex source model.
- Geometrical model: The light source is modeled physically.
- Radiance model: The output of the light source is measured for a representative sample.
- System model: This is a combination of the geometrical and radiance models, which takes the advantages of both systems.
- Physical emission: Photoluminescence is the tendency of certain optically active molecules to absorb, downconvert, and re-emit light at a longer wavelength.
Most light sources can be modeled.
- Source Diffractive: A source with the far-field diffraction pattern of a defined UDA.
- Source Diode: An array of diodes with separate X/Y distributions.
- Source DLL: A source defined by an external user-supplied program.
- Source Ellipse: An elliptical surface that emits light from a virtual source point. This light source can be useful when modeling laser diodes that have different beam divergence in the fast and slow axes.
- Source EULUMDAT File: A source defined by lamp data in an EULUMDAT format file.
- Source Filament: A source in the shape of a helical filament.
- Source File: A user-defined source whose rays are listed in a file.
- Source Gaussian: A source with a Gaussian distribution.
- Source IESNA File: A source defined by lamp data in an IESNA format file.
- Source Imported: A source defined by the shape of an imported object.
- Source Object: A source defined by the shape of another object.
- Source Point: A point source that radiates into a cone.
- Source Radial: A radial symmetric source based upon a spline fit of arbitrary intensity vs. angle data.
- Source Ray: A point source aligned with direction cosines.
- Source Rectangle: A rectangular surface that emits light from a virtual source point.
- Source Tube: A source in the shape of a cylindrical tube.
- Source Two Angle: A rectangular or elliptical surface that emits light into a cone with
distinct angles in the X and Y directions. - Source Volume Cylinder: A volume source in the shape of a cylinder with an elliptical cross-section.
- Source Volume Ellipse: A source in the shape of an elliptical volume.
- Source Volume Rectangle: A volume source in the shape of a rectangle.
For example, it is possible to perform LED modeling with an LED, including the emitting die, the lens enclosure, wire bondings, reflecting dish, and even the electrical terminals.
An LED is placed inside a polar detector and a cross-section plot of output power is produced.
If a more complicated light source does not change the result compared to an approximated light source, the more straightforward light source is a more efficient simulation.
