Enhancing the performance of High-Brightness LEDs
This article has been taken from The Gen Newsletter - Summer 2007.
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The High-Brightness (HB) LED market is growing rapidly, especially in colour signage, LCD backlights, mobile phones and architectural lighting, with new and more technically challenging applications constantly emerging.
HB LEDs have many advantages over conventional incandescent light sources as they efficiently produce single colour light, are reliable, easy to control, and are very compact. Breakthroughs in white light HB LED technology in particular have led to these sources being used in applications such as street lighting, automotive interior and exterior, studio lighting and medical applications, where they could displace existing incandescent sources.
However, white light HB LEDs still struggle to equal the performance of established sources such as tungsten halogen, especially in terms of colour performance. This is assessed primarily by the correlated colour temperature (CCT) and the colour rendering index: CCT is the temperature of the blackbody radiator which best matches the source’s perceived colour; the colour rendering index describes how well a light source renders colour from the point of view of the human eye.
Whilst white light HB LEDs span most of the useful colour temperature range, colour rendition is usually poor. The reason is that a basic white HB LED device usually comprises a blue or UV LED with a phosphor coating. The blue/UV light excites the phosphor producing a relatively broad spectrum of light, but one which includes both the original source light and the phosphor emission – and this impairs colour rendering. Manufacturers have developed HB LEDs with a much better colour rendering performance, but these ‘warm white’ HB LEDs are only available in low lumen output packages. Large numbers are therefore required to generate useful lumen output products, which are both complex to design and costly to run.
Sagentia, however, has successfully developed a groundbreaking alternative. The result of radical thinking, a detailed understanding of semiconductor device physics and deep technology insight, our approach focuses on enhancing the highest lumen output devices currently available. The result is a low cost and optically efficient method of enhancing – to unprecedented levels – the colour performance of white light HB LEDs.
Our solution is attracting significant interest, especially from applications demanding high quality light. In medical applications, for example, high colour rendering performance is critical to enable accurate visualisation of tissue; it is also vital that specific colour temperatures are produced to ensure the light is comfortable to use. In the future, as basic LED devices continue to improve, it is now clear that new technologies such as that developed by Sagentia, will eventually enable HB LEDs to displace conventional sources in many every day lighting applications.
For further information LEDS@sagentia.com