Fluid optics illuminate automotive design

April 1, 2001
The French automobile manufacturer Renault has used an innovative optical system in its new concept car, the Koleos. First shown at the automobile exhibition in Geneva last year, the Koleos uses fluid optic technology in both front and rear lighting systems.

The French automobile manufacturer Renault has used an innovative optical system in its new concept car, the Koleos. First shown at the automobile exhibition in Geneva last year, the Koleos uses fluid optic technology in both front and rear lighting systems. The new system allows fully functional lights to be molded into futuristic shapes that blend with the car's body shape. For instance, the rear lights are all but invisible until activated. The lights were developed and supplied by Megalux (Paris, France).

The Koleos is designed to be a blend of a traditional car and an off-road 4 x 4 (see figure). High-technology elements include a voice-activated screen for essential functions, and the novel optical system. In the arch-shaped headlights, the light from the bulb enters a fluid optic system, which shapes the light and guides it either to the lower-half arch, for the dimmed position, or the upper-half arch, for the full beam position.

Fluid optics is a technology pioneered by a French research group over the past decade and Megalux claims to be the only optics engineering and design department that is currently exploiting the concept. The field grew out of a research project started in 1991, when Jean-Claude Amblard was asked to design a high-power light projector that produced an essentially heat-free beam.

Fluid filters to remove the infrared only partially solved the problem, but further experiments using carefully shaped hollow optics filled with a circulating fluid (temperature-controlled water in this case) brought complete success. The result of this project was the "Phare Doux," a 50-kW projector first demonstrated in 1995, which produces essentially "cold" light.

The research did not stop there, however. Amblard took out patents on his fluid optic technology, and started applying it in other areas. According to Megalux, the concept behind fluid optics is an outgrowth of traditional optics and the optical properties of a transparent moving liquid crossed by an intense beam of light.

"There are two kinds of fluid optics: one with fluid in it to filter the infrared energy (called dynamic fluid optics) and another in which the fluid is replaced by solid (called static fluid optics)," according to Amilcar Vide-Amblard, co-inventor of the technology.

"It is important to understand two things," Vide-Amblard continued. "The shape of our optics comes from studies on fluids in movement. That's why we always talk about fluid optics. We put fluid on optics only if we want to eliminate the infrared energy, typically for high-power transfer."

In practice, the concept involves complicated modeling of optics by using specific curves and optical equations derived from the study of fluids. Invaluable in the optic design are two pieces of Megalux software. "Horus" is a two-dimensional optical simulation package, while "Khnoum" is a three-dimensional package that enables prediction of results without building a prototype.

As a first step the light source is carefully characterized. The source parameters are fed into the software, which can then suggest optical designs to obtain the required results. Complex shapes are considered, which can take any form, with or without skew, and are not limited to the usual combinations of parabolas and ellipsoids. Finally, a prototype is built using CAD files generated by the software.

The prototypes are usually built partly in metal (aluminum, steel, or brass) by milling and countersinking. Some are built in quartz, or even high-optical-quality polymers. Both the carefully shaped container and the fluid, or solid, contained in it combine their optical properties to give the refractive or reflective effect required. Beam combination is a technique often called for, and readily achieved with fluid optic designs.

The reduction of heating effects has proved useful in many applications. The fluid is selected according to its luminous bandwidth and the conditions of use. In the new Renault system, for example, the design parameters given to Megalux included maintaining the usual function of the headlights, with high-quality optical surfaces, but in a shape that is something like half a nose cone.

To obtain dimmed headlights, a fluid reflector, which does not occlude the beam, passes the light into the lower half of the cone. The whole reflected beam is used, giving extra light to the dimmed beam. The "full beam" is achieved through a second fluid reflector, which collects the light and passes it to the upper half cone.

The parameters for the rear lighting were more stringent. Renault's design team wanted to hide the light source, having it apparent only when lit up. Megalux used holographic optics combined with fluid optics technology to achieve the effect.

For each function, the light is first filtered to obtain the desired color, then directed via fluid optics to narrow transparent bars mounted on the back of the car. A hologram, located in the middle of each bar, redirects the light to the rear of the vehicle, through perfectly smooth glass. The lower bar performs the blinking function, while the upper bar performs the dimmed-rear-light function. Finally, the brake light is obtained from the dimmed light by increasing the beam intensity.

Applications currently being tackled with fluid optics at Megalux include beacon design for airports and lighting for panel displays in aircraft. Megalux is also installing internal lighting systems, such as uniform cold lighting for art galleries and a new lighting system for the Paris Metro. Another ambitious project aims to use fluid optics in external street-lighting systems, providing street lamps with the light source at ground level, for easy maintenance, with optics directing the beam overhead.

About the Author

Bridget Marx | Contributing Editor, UK

Bridget Marx was Contributing Editor, UK for Laser Focus World.

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