Use the Illuminated Surface node to release rays under the assumption that the emitted rays are specularly reflected from an external radiation source. It is assumed that the entire selected surface has direct line of sight to the external radiation source; that is, shadowing due to other geometric entities is not taken into account.

See Release for information on the following sections: Release Times, Initial Ray Frequency, Vacuum Wavelength, Initial Phase, Initial Polarization, and Initial Value of Auxiliary Dependent Variables.

See Release from Boundary for information on the Initial Position section.

Select the Rays to release: Reflected (the default) or Refracted.

Select an Incident ray direction vector: User-defined direction (the default), User-defined point source, or Solar radiation (3D components only).

For User-defined direction enter the components of the Incident ray direction vector Li (dimensionless) based on space dimension.

If User-defined direction or Solar radiation is selected from the Incident ray direction vector list, you can include small perturbation factors designed to take the finite size of the sun (or another light source) into account. Select an option from the Corrections for finite source diameter list: None (the default), Create light cones at release points, or Sample from conical distribution.

For Create light cones at release points and Sample from conical distribution, specify the Maximum disc angle Ψm (SI unit: rad). The default is 4.65 mrad, approximately the size of the solar disc when viewed from Earth.

For Create light cones at release points and Sample from conical distribution, select a Limb darkening model: None (the default), Empirical power law, Linear, or User defined. The limb darkening model reduces the intensity of solar radiation that is released from the periphery of the solar disk, relative to radiation that is released near the center. For Linear enter a Limb darkening coefficient β (dimensionless). The default value is 0.8. For User defined enter a Limb darkening coefficient fL (dimensionless). The default value is 1.

Select the Include surface roughness check box to include an additional perturbation term based on uncertainty in the orientation of the surface normal, which is common in imperfect reflecting surfaces. Enter a value or expression for the Surface slope error σ (SI unit: rad). The default is 1 mrad. The surface normal is then perturbed by a random angle, which is sampled from a Rayleigh distribution.

This section is available when the ray intensity is solved for. Enter a value for the Incident ray intensity Ii (SI unit: W/m2). The default is 1000 W/m2.

Enter a Total source power Psrc (SI unit: W). The default is 1 W. In 2D, instead enter the Total source power per unit thickness Psrc (SI unit: W/m). The default is 1 W/m.