LED Tail Lamp Design Using Different Design Strategies for Different Optical Effects

Thomas L.R. Davenport, Ph.D., Systems Engineer,Software Marketing,

Optical Solutions Group, Synopsys, Inc., 5255 E.Williams Circle, Suite 5200, Tucson, AZ 85711, USA

Thomas.Davenport.@synopsys.com

Abstract

The two most important aspects of taillamp design are: intensity test point performance and creating a pleasingspatial distribution.  Often the latteraspect is critical for brand distinction, and thus just as important as passingtest point requirements.  In this work,we briefly discuss many of the (United Nations) ECE intensity test point specificationsinvolved in tail lamp design.  Then, wemove on to the design of optical systems for different tail lamp functionsusing LED sources. Each design type considered is tested and optimized to meetits ECE intensity point specifications as well as for achieving a pleasingspatial distribution.

For example, the stop lamp is designed using an LED source inconjunction with a faceted reflector.  Asurface construction approach that modifies a base paraboloid in the horizontaland vertical directions is developed and explained. The visual and intensityperformance effects from changing: the base surface focal length, types of facetspreading (divergent or convergent), amount of spreading in the horizontal andvertical directions, the number of facets in each direction, and the specularityof surface finish are all taken into account in the design process.

Light guide designs are also developed and the difference indistribution for different extraction shapes is optimized.  Light guide designs can be challenging sincespatial uniformity is typically desired for a pleasing distribution, while aparticular angular distribution is required for meeting the intensityspecifications.  Often meeting both ofthese requirements concurrently is difficult, since typically only one opticalsurface is allowed to be changed. Therefore, the depth, spacing, and shape of the extraction elements maybe modified and optimized to create the desired distribution.  Additionally, practical designs require adraft angle so that they can be pulled from a mold as well as a fillet radius,since infinitely sharp corners are not possible to mold.  All of these issues are considered in thedesign developed here.

Tailored, arrayed refractive optics are also considered.  Here each optical element is designed using anovel tailoring approach involving an iterative compensation technique tocreate a specific intensity distribution. The intensity distributions from each element are then superimposed tocreate the full design.

Keywords: Tail lamp, faceted reflector, light guide, LED, stoplamp