Surface Source Properties

View Data	When a Source Property type surface source is selected, you can open the
Button	Surface Source Property Editor to view the property data by clicking the View
	Data button.
Color	You can change the color of the rays by emitted by the source. To make this
	work you must also change the selection in Analysis|Ray Colors. Choose
	Source-based ray colors to have rays displayed in the source color.

Angular

Distribution

Rays

Select Lambertian, Normal to Surface, Surface Absorptance, or Uniform.

Surface Sources emit light in one of the four angular distributions. Specifying angles and probabilities for the rays is important for the accuracy of the raytrace.

Lambertian — Emits radiation with a cosine-weighted angular distribution.

Normal to Surface — Emits radiation in a direction perpendicular to the surface. This option allows you to use a sphere to generate a diverging spherical wavefront (as from a point source) or the inside of a spherical shell to generate a converging spherical wave

Surface Absorptance — Uses the absorptance vs. angle of incidence profile specified by the surface's Surface Property as an angular emissivity distribution for emitting rays. The wavelength dependence is also used as the spectral emissivity for blackbody and graybody sources.

Uniform — Generates rays uniformly into a hemisphere. This allows you to use a flat surface to simulate a point source, i.e. one with a spherical symmetry.

You can select All rays, Only random rays, or Only importance rays. Source Importance sampling must be applied to the surface to have any rays emitted when Importance Sampled Rays is selected.

Discrete	Here, a wavelength refers to a single discrete wavelength. For a raytrace that
Wavelengths	uses many wavelengths, TracePro lets you optionally specify a mathematical
	weight for each wavelength to enhance or diminish the role of the wavelength
	in calculations.
Calculated	The From and To limits of each waveband are shown. There can be many
Wavelengths	wavebands used in a raytrace calculation. TracePro calculates zero or more
	spectrally-weighted wavelengths for each waveband, as determined by the
	#Inc entry. Rays are traced at the spectrally-weighted wavelengths. Calculated
	wavelengths are used with Source Property, Blackbody, and Graybody sur-
	face sources.

Blackbody Surface Sources

A blackbody absorbs all light incident upon it and emits light in a spectrum derived from the quantum theory of radiation (the Planck blackbody distribution) in a Lambertian angular pattern. The spectral distribution of rays depends on the temperature of the surface.

Approximating a blackbody can be done by creating a cavity and allowing light to escape through a small hole. Most surfaces are poor approximations to a blackbody, but some surfaces (e.g. some special black paints) can approach blackbody performance over a limited range of wavelengths.

Note: By Kirchhoff’s law of radiation, the absorptance of a surface is equal to its emissivity. To rigorously simulate thermal radiation in TracePro, you must select the Surface Absorptance Angular Distribution. Then TracePro uses the absorptance of the surface as the emissivity. If you select a different angular distribution, TracePro sets the emissivity to one.

TracePro 5.0 User’s Manual

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