Like headlights, tail lights too have come a long way since the incandescent bulbs. Designers previously incorporated secondary collection optics like metalized parabolic reflectors to gather and reflect back the light out of the tail light at the required beam angles and lumens to meet minimum levels set by the Department of Transportation (DOT). Some of the reflectors incorporated the pillow type optics to create multiple images of the single incandescent light source.
The introduction of LEDs has opened up a new universe to tail light designers with new challenges as well as design liberties to create limitless and unique tail lights seen on the roads today. LEDs are a unidirectional light source, emitting light only in the forward direction. This has eliminated the need for reflectors and tail lights have become much slimmer. The initial less creative tail light designs faced the LEDs directly at the following vehicles, creating a highly pixelated bright look, disturbing to many drivers of vehicles following. Many however were ready to spend on this expensive option regardless.
German car manufacturers were the first to introduce LEDs in their designs and also the first to improvise on the uniformity of their tail lights. Manufacturers incorporated uniform ‘night time design elements’ that were accomplished by edge lit designs incorporating LEDs at the input end of a light pipe. The light guided through the light pipe on the principles of total internal reflection, similar to the principle of fiber optics, until they encountered a ‘rib’ or other micro-structure that allowed the light to escape, creating a uniform and distinct glowing design element giving each brand its distinctive identity. American car makers preferred a less expensive route that delivered a brighter design element than a light pipe design could deliver.
They kept the direct view orientation of the LED and incorporated a tertiary optic or diffuser to create the uniform look. German car manufacturers continue to push the boundaries of tail light design. The latest development is the use of white diffuse reflector materials in indirect lighting configurations. In this the LEDs are pointed away from the exit aperture of the tail light. This configuration suits the purpose of increasing the path length of the light to make the tail light even more uniform and slimmer.
Up until just recently, the uniform design aesthetics were only being applied to night time design elements. We can now see vehicles that have super uniformity in the brake light section of the tail light. There even are tail light units that combine brake light and night time design elements to give a single uniform look while at the same time, meeting all the DOT mandatory requirements.
LED modules are becoming the integrated circuits of the solid-state lighting industry, the same way as microcontrollers evolved. LEDs are increasingly being marketed in a modular format for limitless applications. The advantages too are similar. They are faster and easier to design and lower the overall cost through reduced component count and smaller form factor.