Introduction
PHILLIPS
New look: Philips' Lumalive photonic fabric is expected to make its debut in clothing and furniture upholstery in 2007. The technology relies on an LED array fabricated on a thin, flexible substrate.
Optical fibres and LEDs are already well established in the fields of optoelectronics and telecommunications, but few people realize that the technology is now being applied in the textile industry to striking effect.
Scientists have now learnt how to 'knit' optical fibres and integrate them with textiles as well as manufacture flexible LED arrays and light-emitting fabrics. The result is a new breed of visually striking photonic clothing that not only looks good but also has serious applications as 'light bandages' (medical dressings containing their own light source) and garments with enhanced visibility and dynamic signage for pedestrians and cyclists.
Although the flexible thread-like characteristics of optical fibre may give it the impression of being an easy material to weave, knit or stitch into fabrics, in practice the fibres have proved far more difficult to handle than normal threads. The task is complicated further by the need to connect the fibres to a light source, supply electrical power and ensure that the ensemble can be washed. That said, several companies and institutions now seem to be making good progress and are on the verge of making photonic textiles a commercial reality.
"The idea of trying to integrate optotelectronics and electronics into clothing has been around for a while," said Janet Hansen, founder of Enlighted Designs, a maker of bespoke fashion clothing in Encinitas, California. "Back in the disco-dancing 1970s people were making illuminated clothing by stitching incandescent bulbs onto fabrics," she added. These days companies like hers use more practical light sources such as LEDs or flexible electroluminescent (EL) materials such as EL Wire. One Italian company called Luminex, which also has a focus on fashion, has created stunning garments out of luminescent optical fibres that were initially designed for particle-physics experiments. With these kinds of approaches the results can be dazzling.
"In general, people wear illuminated clothing to stand out in a crowd, and make an exaggerated fashion statement," said Hansen. Over the past decade she has made just about every kind of garment from wedding dresses to bras, each handmade with each and every one of the conducting leads from the LEDs painstakingly sealed with an insulating epoxy. This makes them waterproof enough to at least hand wash. "The lighted bras have been especially popular," she said.
More recently both Philips and France Telecom have developed their own technology and demonstrated clothes that boast dynamic displays that the user can control at will.
Philips' product, dubbed Lumalive, consists of arrays of inorganic LEDs mounted on flexible substrates, which are then slipped into a pocket behind the outer fabric. What makes Lumalive so striking is the use of the surface fabrics to diffuse the light from the LED array, said Martijn Krans, technology manager for the Philips Research Photonics Textiles group. "By diffusing the light you can still experience an animation of quite high resolution with only a limited number of pixels." And yet because the LED array is less than two millimetres thick and behind the fabric, there is no visible sign of the components when the power supply is switched off. "We're ready to put the technology to the market," said Krans.
Products are expected to hit the market later this year with an initial focus on promotional purposes, as well as use in safety clothing and furniture upholstery. In the meantime the company is continuing to refine the technology making the flexible LED substrates thinner and more flexible.
Another company with safety in mind is Lumitex based in Strongsville, Ohio. It also started out using optical fibres to create light-emitting garments as long ago as 1985. But at the time, with the world not quite ready for such bold fashion statements, the company quickly moved on to medical applications.
One of its first products was a light-emitting blanket called a Bili-Blanket, a flexible woven fabric that emits a blue light — with a wavelength between 390 and 475 nm — to treat jaundice in newborn babies. This form of light therapy is necessary in order to break down the excessive levels of bilirubin, allowing it to be excreted. Normally the only way to carry out this treatment is to put the newborn under a blue lamp. But this can be distressing for the baby as it has to lie there and cannot be held, Peter Broer, president of Lumitex, pointed out. With Bili-Blanket it is very different because the babies can receive the treatment while being cuddled and fed, by wrapping them in a light-emitting blanket. "We are bringing the light to the babies," he added.
The blankets consist of two layers of parallel optical fibres, made out of acrylic polymer, which are woven together with polyester cross fibres. The ends of the optical fibres are bunched together at one side and plugged into a light source.
LUMINEX
Accessories with a difference: the origins of Luminex's striking fabrics lie with luminescent optical fibres that were initially designed for helping scientists detect subatomic particles in physics experiments.
Ironically, Lumitex's optical-fibre textiles rely on achieving what all telecom engineers desperately try to avoid — light leakage. In optical communications great effort goes into ensuring that light cannot escape from the fibres and that they act as a low-loss light pipe. In contrast, Lumitex tries to ensure that as much light is emitted and scattered from the fibres as possible. Ingeniously this is achieved by ensuring the weaving pattern bends the fibres beyond a critical angle to efficiently scatter the light out of the fibre. "By controlling the bends and the spacing of the fill thread we can control the amount of light escaping," said Broer.
Another advantage of the Lumitex approach is that the light produced is cool, because the light source is remotely located. This is particularly important with one of its more recent products, the LightMat. This flexible light-emitting fabric is now being used by surgeons to illuminate body cavities during surgery. When attached to a substrate that can be bent to any kind of shape, the device can be attached to most surgical instruments to provide cool and shadowless light, when compared with the traditional head lamps, over-head lamps or light pipes, said Broer.
LUMINEX
Centre of attention: Luminex's optical-fibre fabric has proved popular for making upholstery.
LightMats have been on the market for about three years, costing less than $60 and Lumitex is now working with companies to make flexible, illuminated keypads for electronic devices and even illuminated hot tubs.
Markus Rothmaier at the Swiss materials science and technology research institute EMPA, is also developing light-emitting fabrics for medical purposes. Photodynamic therapy involves activating a cancer-killing oxidizing dye with light as it concentrates around a tumour. He pointed out that it is extremely important to get the exposure right, because too much active dye can damage healthy tissue and too little will have no effect on the tumour.
Needless to say this makes treatment a challenge. "It's very difficult for the doctor to control the light doses," he said, owing to the shape of the body and limited accessibility. However, if flexible light sources could be wrapped around target sites, or inflatable light-emitting membranes inserted into orifices such as the mouth or throat, then the dose could be much more easily controlled, he pointed out.
But one of the biggest challenges remaining with photonic textiles is actually weaving, stitching or knitting with these fibres, said Rothmaier. "Very often the optical fibre just breaks," he added. His own technique involves embroidering loops of optical fibre onto an existing fabric substrate, which puts less stress on the fibres than weaving or knitting.
Contrary to popular perception, it may be the medical world rather than the fashion industry that drives the photonic fabric technology forward and ultimately becomes its most important application.
