Understanding the Parameters of a TIR Lens
This page describes the parameters to set when creating a TIR Lens.
A TIR lens should be seen as a two-sided lens. The support plane represents the bottom of the lens and the output face represents the top of the lens.
Light travels from the inner to the outer part of the lens.
_OPD_TIR_Lens_View_Section.png)
Axis System
The TIR lens is build around a central axis called revolution or optical axis. This axis is normal to the support plane.
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Source position: the source position is set by selecting a point. This point places the light source in the scene and will be used to build the TIR lens around it. The source set here is considered as punctual, which means that it is a simplified source that emits light from a single point and position.
Note: The source of the TIR belongs to this optical axis. - Support planeSupport point: the support defines the TIR lens bottom face.
Dimensions
- Input radius: internal radius of the TIR Lens on the support plane.
- Depth: distance between the support plane and the first intersection with the lens along the revolution axis.
- Draft angle: angle between the internal component of the lens and the revolution axis.
- Support Thickness: The TIR Lens is considered fastened on a support (represented by the support plane). The support thickness refers to the thickness of the ring at the bottom of the lens.
- Thickness: height of the TIR lens along the revolution axis.
- Output radius: radius of the lens' output face.
_OPD_TIR_Lens_View_Side.png)
_OPD_TIR_Lens_View_Angle.png)
_OPD_TIR_Lens_View_Bottom.png)
TIR Lens side view TIR Lens angled view TIR Lens bottom view
Refractive Index
The Refractive Index of a material is a pure number that describes how light propagates through that medium.
Most transparent materials have refractive indices between 1 and 2. Here the refractive index refers to the index of the lenses' material.
Focal
The focal length represents the distance between the source and the top of the internal collimating surface.
Spread Parameters
Spread and Spread Behavior
The Spread and Spread behavior parameters spread the light at an angle determined on an intensity target.
_TIR_Lens_Spread.png)
The Spread value controls the maximum angular aperture for the center (dioptric) and the outer (TIR) faces. By defining a Spread value higher than 0°, TIR lens will spread light an intensity target.
The Spread behavior influences the results whether the TIR Lens is Convex or Concave.
- When the TIR Lens is concave: the TIR face spreads from max aperture to 0°, meaning rays are crossing.
- When the TIR Lens is convex: the TIR face spreads from 0° to max aperture, meaning rays are opening.
| Concave TIR Lens | _TIR_Lens_Concave.png) |
_TIR_Lens_Concave_Result.png) |
| Convex TIR Lens | _TIR_Lens_Convex.png) |
_TIR_Lens_Convex_Result.png) |
Spread Control
The Spread Control parameter manages how light is spread between 0° and Spread Max.
- When Spread Control is lower than 50, light accumulates on 0° direction.
- When Spread Control is higher than 50, light accumulates on Spread Max direction.
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Mode Convex Spread = 30° |
Mode Concave Spread = 30° |
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| Spread Control = 0 | _TIR_Lens_Convex_Spread_Control_0.png) |
_TIR_Lens_Concave_Spread_Control_0.png) |
| Spread Control = 50 | _TIR_Lens_Convex_Spread_Control_50.png) |
_TIR_Lens_Concave_Spread_Control_50.png) |
| Spread Control = 60 | _TIR_Lens_Convex_Spread_Control_60.png) |
_TIR_Lens_Concave_Spread_Control_60.png) |
| Spread Control = 100 | _TIR_Lens_Convex_Spread_Control_100.png) |
_TIR_Lens_Concave_Spread_Control_100.png) |