Light Guide Prism Parameters

This page describes all the parameters to set when defining prisms.

Note: Prism parameters vary depending on the operation selected.


Step (Add/Remove Operation)	Step corresponds to the spacing between the mid points of the top edges of two adjacent prisms. CAUTION: Make sure to define a Step value different from the Length value. Otherwise it may generate unwanted prism geometries.
Step (Hybrid Operation)	Stepcorresponds to the spacing between two adjacent prisms projected on the guide curve. CAUTION: Make sure to define a Step value different from the Length value. Otherwise it may generate unwanted prism geometries.
Length (Add/Remove Operation)	Lengthcorresponds to the length of the prisms. If the offset is too low regarding the profile, a part of the prisms can be created inside the body. As a consequence, the length of the prisms can appear as not being taken into account. CAUTION: Make sure to define a Length value different from the Step value. Otherwise it may generate unwanted prism geometries.
Trimming ratio (Hybrid Operation)	The trimming parameters allows you to cut off the prism either from their peak or from their base: Bottom trimming controls the prisms from their base. Peak trimming controls the prisms from their peak.
	Prisms without trimming	Prisms trimmed from the bottom	Prisms trimmed from the peak
Offset (Add/Remove Operation)	Offset corresponds to the distance between the guide curve and the middle point of the top edge of the prism. Make sure to set appropriate values for the offset parameter: With Add, if the offset is too low, the prisms are inside the body. With Remove, no material is removed from the body if the offset is too high.
Offset (Hybrid Operation)	Offset corresponds to the distance between the guide curve and the bottom of prism (start angle side).
Width	Width corresponds to the width of the prisms. Width can be constant over the guide or can vary (Control Points or Input File). Width is always constant in Hybrid Operation.
	When the width varies, the width is progressive in Add Operation.	When the width varies, the width is progressive in Remove Operation only if at least two prisms touche themselves (without considering the milling).	When the width varies, the width is not progressive in Remove Operation if prisms are all separated. When the milling make two prisms touch each other, the progressive width is not activated. The criterion to determine whether two prisms touch each other is done without the milling.
Start angle End angle	Start angle and End angle correspond to the angles of the prisms to local neutral fiber (tangent line to guide curve). Start Angle corresponds to the source side angle of the prisms (84,3° in image below). End Angle can be seen as the angle used to change the direction of a reflected ray to let the ray get out of the Light Guide (10,7° in image below). In Add or Hybrid mode, if the start angle is set to automatic, a constant angle of 85° is used to calculate the prisms' start angle. In Remove mode, if the end angle is set to automatic, a constant angle of 85° is used to calculate the prisms' end angle.
Start Radius End Radius	Important: The computation time may be longer when you create curved prisms using the Start radius and End radius parameters. Start radius corresponds to the radius of curvature applied on the source side face of the prisms. End radiuscorresponds to the radius of curvature applied on the non source side face of the prisms. Apply a positive value for a convex curvature and a negative value for a concave curvature. Important: The Start and End Radius is always applied on the edges of the complete prism. In other words, if you apply a radius on prisms that are partially added or removed according to your setting, the radius is applied on the complete prism edge and not on the partial prism edge. In the following example, you have a prism to remove (yellow). When you apply a radius, the curvature part is generated from the complete prism edge (green), and not from the partial prism edge (red):