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The energy and light efficiency of these displays is of para- mount importance especially in portable electronics because it determines brightness and battery-life and, consequently, flat-panel displays that use ambient light effectively are much sought after. In order to enable sufficient readability in low- lighting environments, here we report on a new illumination principle for use with reflective displays based on extraction of light from a lightguide by diffraction at slanted phase grat- ings with a sub-micrometer sized periodicity. Despite a large variety of new display principles that were proposed based on organic or polymeric light-emitting diodes, field emission, electrochromism, and electrophoretic effects, displays based on liquid crystals (LCDs) have maintained their dominant position in the field. This is related to their low power consumption, low voltage operation, long lifetime, and an impressive technological progress which was made in improving these displays with respect to switching voltages, switching kinetics, multiplexing capability, and viewing angle using new switching and addressing principles and specially designed optical films. [1±10] The energy and light economy of traditional transmissive LCDs is notoriously poor. In most LCDs less than 10 % of the light generated by the source actually reaches the viewer. [1±10] This poor efficiency is predominantly related to the use of ab- sorption-based polarizers (light efficiency < 50 %) and color filters (light efficiency < 33 %), which reduce the brightness of the displays and impose a major energy drain on the batteries in portable applications. Nowadays, polarizers and color filters based on light reflection or scattering are available which of- fer the opportunity to recycle the non-desired light compo- nents and which enhance the device efficiency. [1±10] Simulta- neously, for portable applications there is a demand for an increased use of ambient light in the illumination of LCDs. For instance, in so-called transflective LCDs (e.g. a cellular phone display), semi-transparent reflectors are employed that use ambient light to generate the image in a bright environ- ment. An additional illumination means at the rear of the dis- play (a so-called backlight) is used for operation under darker conditions. Also, the advent of color displays in mobile appli- cations enhanced the dependency on illumination systems even more. In these transflective displays both the ambient light and the artificial light are used rather ineffectively due to the partially transparent (± 30 %) and partially reflective (± 70 %) nature of the transflector. Of course, optimal use of ambient light is obtained in fully reflective LCDs. In that case, a so-called frontlight is needed for illumination of the LCD display in a dark environment. [11] The viewer looks at the dis- play through the frontlight, which is a transparent waveguide system mounted on top of the display. An important draw- back of such a frontlit LCD, in fact delaying its commercial in- troduction, is that the visual perception is rather poor. This is caused by the visibility of the light out-coupling structures in the waveguide, which superimposes on the observed image. Additionally, the light out-coupling is usually rather poorly se- lective towards the LCD-side, i.e., a significant portion of light is emitted directly to the viewer, which distorts the visual in- formation on the display by reduction of the contrast and col- or saturation. There is a persistent demand for new illumination systems for frontlit, reflective LCDs, which combine a range of desir- COMMUNICATIONS 2108  2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/adma.200400330 Adv. Mater. 2004, 16, No. 23±24, December 17 ± [*] Prof. D. J. Broer, Dr. H. J. B. Jagt, Dr. H. J. Cornelissen Philips Research Laboratories (WAG 11) Prof. Holstlaan 4, NL-5656 AA Eindhoven (The Netherlands) E-mail: Dick.Broer@philips.com Prof. D. J. Broer, Dr. C. W. M. Bastiaansen Dutch Polymer Institute Chemical Engineering and Chemistry Eindhoven University of Technology P.O. Box 513, NL-5600 MB Eindhoven (The Netherlands) [**] The authors express their gratitude to the Dutch Polymer Institute for financial support.