The use of freeform optical elements in non-imaging technical areas becomes a very important role nowadays. Many applications that can be found in architecture/street lighting, technical illumination and automotive interior lighting require complex target distribution. Given relatively compact sources such as LEDs freeform optical elements can be precisely tailored to meet specific target requirements by providing high energy efficiency.
For the optical designer of freeform components, it is essential to get appropriate calculation techniques integrated into an illumination-design software package. This would allow the designer to develop more complex lighting systems and analyzing them by Monte Carlo raytracing methods subsequently.
As part of its LightTools illumination design software, Synopsys recently introduced the Freeform Designer as an integrated capability in the software’s Advanced Design Module. The Freeform Designer can be used to calculate freeform reflective and refractive surfaces based on an illuminance or intensity target distribution, source collection angle and distribution, and several other geometrical settings. The following examples highlight some practical considerations when designing freeform illumination optics.
A freeform lens is designed to project a complex target onto a nearby plane.
This is an example of a complex target.
A freeform lens with an LED source is designed to produce a wide-angle, elliptical Gaussian distribution.
Here, a 25 × 25 grid of points describes the surface, with a calculation time of a few seconds.
The resulting intensity distribution is shown on the right.
A rectangular freeform reflector transfers light from an LED to a circular lightpipe. The reflector is designed to cross the rays on the way to the target at the front face of the lightpipe, creating an intermediate focus and allowing the rays to clear the source.
This image compares two freeform lenses with the same intensity target specification. For both lenses, the rays (in red) at the edge are near the critical angle, indicating that the freeform surface is near the limit of collection. In the left image, the source (shown as a blue sphere) is at the nominal position and has a full collection angle of 100°. In the right image, the first lens surface is a Cartesian oval, and the source has been moved toward the lens, increasing the full collection angle to 140° and enabling the collection of substantially more light.
The integration of a capability that quickly and easily calculates freeform surfaces in the LightTools design software environment will allow for greater use of freeform optics in illumination by facilitating their design and analysis.
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