Publication date: 02 December 2008
A top priority for today’s instrumentation designers is to achieve a compact, low-profile solution. This calls for thin lighting devices, which leave more space for core functional components of the system, and also allow the panel layout to be determined according to human factors considerations, rather than physical constraints imposed by bulky components.
At the same time, achieving comfortable, consistent and uniform illumination is essential to achieve a positive user experience. Sources such as LEDs and electroluminescent (EL) lamps enable designers to meet many of these criteria.
The performance of LEDs in HMI applications is ultimately determined by the techniques used to manage and direct the emitted light. Rather than mounting an array of LEDs on a dedicated PCB directly behind the front panel, lightguides are often used to conduct light from LEDs mounted on the edge on the panel into the area to be illuminated.
This eliminates the cost of the dedicated PCB, and also allows advantages such as precise positioning, close spacing of status-indicator lamps, and uniform illumination of larger areas. However, the chosen light-guide technology has an important effect on the quality and function of the end result, as well as factors such as cost and time to market.
Applications for LEDs in modern vehicle interiors provide several examples of how an optimal combination of light source and lightguide influence the success of the end product. Leading design trends are extending the use of lighting beyond straightforward instrument backlights to create new types of functional lighting, orientation lighting and overhead systems, particularly in high-end vehicles. Emerging applications include illuminated switch surrounds, door controls, dome lamps, vanity lamps, and ambient lighting to enhance the cabin environment in general.
Woven fibre optic cables and injection-moulded lightguides are both established technologies for distributing light to a desired location, such as the graduated perimeter of a dial. However, several pressures are exposing shortcomings in these technologies. These include carmakers’ desires for smaller and lighter instrument panels, faster installation on the assembly line using minimal clips and fixings, and better lighting of inaccessible areas in the vehicle cabin.
In addition, the high up-front investment in tooling required to build an injection-moulded lightguide tends to increase cost and slow project completion. Design changes are also time consuming and expensive to implement, either during the initial project or during subsequent evolution of the end product.
Printed lightguides for LEDs offer a solution to the size, cost and turnaround challenges now facing conventional fibre optic or injection moulded technologies. Building on processes already proven in the manufacture of membrane keypads, with a number of patented enhancements, it is now possible to produce ultra-thin lightguides by a series of screen printing operations.
By eliminating the tooling for a conventional injection moulded component, printed lightguides can be produced at lower initial investment. They can also be modified easily in response to design change requests.
Also, by combining the technology with capacitive touch sensors, imaginative designers have shown that an illuminated switch panel less than 1mm thick is achievable.
Printed lightguides also allow LED-based designs to match the advantages of EL technology, which include an extremely low profile and the ability to create complex shapes by die-cutting the EL material. At the same time, however, LEDs also support a far wider range of colours than can be achieved using EL sources, while their low-voltage operation simplifies electrical design by eliminating the high-voltage inverter necessary to operate an EL lamp.
As a specialist designer of automotive products including interior systems, International Automotive Components (IAC) is familiar with the opportunities and challenges surrounding the use of LEDs in automotive design. The company has delivered successful LED-based interior lighting solutions to top brands, and has recently used printed lightguides to innovate solutions for orientation lighting and functional lighting.
To aid selection of lighting technologies for various vehicle interior systems, IAC compared the merits of LEDs fitted with woven fibre optic, injection-moulded or printed lightguides against the properties of EL technology. Engineers identified 19 key criteria, spanning issues governing functionality, cost and turnaround time.
According to IAC’s Carter Cannon, the most important of these are the ability to achieve harmonious surface illumination, longevity, robustness, quality and reliability, performance, time to market, and piece price. Although EL lamps scored highly in terms of harmonious surface illumination, LEDs with printed lightguides outperformed EL lamps and conventional lightguides in most other respects. Piece price, for example, is a particularly important aspect for automotive suppliers; here, printed lightguides offer cost savings over other lightguide technologies as well as EL solutions.
IAC’s results also showed that printed technology is more responsive to design changes, while at the same time matching fibre optics and injection moulded lightguides in terms of formability, mould-ability, reliability and robustness.
On the other hand, printed lightguides are clearly superior for illuminating clearly defined, segmented areas. Flexible lighting-control modes and effects such as animation are also much better supported, compared to the older technologies. Moreover, with fewer separate parts helping to reduce assembly complexity and allow easier integration, printed lightguides deliver additional benefits ultimately delivering increased performance and reduced cost.
IAC has used these advantages to propose imaginative new interior lighting solutions for its customers in Europe.
Combining low-profile LED lighting with finishes such as piano black, chrome and other metallic effects has excited makers of high-end vehicles, who are now considering further uses for printed lightguides to deliver new and better experiences for their customers.
“Printed lightguides open up many new possibilities to improve function as well as appearance using lighting,” comments Carter Cannon.
“The comparison matrix we developed is helping us to identify even more applications, and working together with Design LED and our customers we can envisage dramatic changes to the in-car environment. I am sure this technology will have similar impact in many other lighting applications.”
Printed lightguide assemblies are built using processes already proven in the manufacture of membrane keypads, combined with additional patented processes to create a multi-layer optical structure. The complete assembly comprises a flexible PCB, side-emitting LEDs and printed lightguides, and finally an upper graphic. The entire “sandwich” has a total thickness of just 1mm, allowing designers to create thin layers of light or illuminated graphics on the outer surface of almost any product. A flexible tail connects to the host motherboard.
This construction frees engineers from the need to install light bulbs or a PCB populated with top-emitting LEDs directly behind an area to be illuminated. Large surfaces up to around 50cm x 50cm can be illuminated evenly, creating a perception of high quality by eliminating inconsistencies such as brighter or darker areas, shadows, or discernible colour shifts. Segmented patterns of light can also be produced, in a choice of colours or even continuously changing colours, while further options for imaginative designers include animation and dynamic branding.
Design LED has also combined its printed light guide technology with capacitive touch sensing to create illuminated touch controls for use in vehicles, domestic appliances, security systems, portable products, industrial equipment and many other applications.
For Further Information, Please Visit http://www.iacna.com or http://www.designledproducts.com
