Bart Andre Salters

LED-based mini-projectors

We have built a mini-projector with LED light sources that is sufficiently small for portable applications. The projector has a three-panel architecture with transmissive LCD micro-displays in order to combine a high lumen output with a low cost price. The volume of the light engine is 100 cc.

58.4: A Handheld Mini-Projector Using LED Light Sources

We have built a mini-projector with LED light sources that is sufficiently small for portable applications. The projector has a three panel architecture with transmissive LCD micro-displays in order to combine a high lumen output with a low cost price. The volume of the light engine is 110 cc. The projector can deliver up to 15 lumen to the screen at a LED power of 9 W. In the high efficiency mode the output is 8.5 lumen at 3.8 W.

Light-guide-based optical engine for light-valve projection

We present a new type of optical engine for projection displays. The optical engine is based on a light guide with embedded color filters. It is intended for three-panel projection displays with micro-display panels of the transmissive type. The light guide serves the purpose of integrating the light and guiding the light to each of the three panels. Proximity illumination is used to illuminate the micro-display panels: the exits of the light guide are in close contact with the entrance of the panel. The optical design considerations underlying the principle of using light guides are discussed. Among these considerations are measures required to prevent light leakage. We also discuss light guide based optical engines relying on the principle of color recycling and polarization recycling. The results of simulations and experiments on a prototype are discussed. It is shown that the use of light guides enables a very compact design. The lumen output of such a projector can be comparable to, or even better than that of conventional systems.

Large, thin, flexible and low-cost light emitting surfaces

Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy efficiency. At the same time, packages emitting enough lumens for lighting applications are decreasing in size. This smaller packaging enables several new applications. In this paper we will discuss one of these new applications: low cost, large, flexible and very thin light emitting surfaces. Our approach consists of using very thin transparent lightguides. Due to their limited thickness, these lightguides are quite flexible. Tiny low power, side-emitting LEDs are used to couple light into these lightguides. A carefully calculated outcoupling structure ensures light is coupled out uniformly. Although this general principle is known, some aspects are new to our approach. The flexibility of our thin lightguides can be very useful for numerous lighting applications; a radius of curvature of just a few centimeters is easily obtained, while still maintaining good outcoupling and uniformity. Furthermore, we show that for several geometries, a perfect homogeneous brightness can only be obtained using a precise pattern and density distribution of outcoupling structures.

Color reproduction for LED-based general lighting

Solid State Lighting is becoming increasingly more advanced, both in terms of lumen output as well as energy efficiency. However, implementation in color consumer lighting products, such as the Philips Ambilight television sets, still requires improvements in both color reproduction as well as intensity uniformity. To build a lighting system capable of correctly reproducing a large color spectrum, 3 primary colored LEDs are required. However, this approach causes problems. In particular, the generation of a white color without color fringes is difficult to implement, as the total amount of light from each primary color should ideally be identical at each position within the light bundle. Our paper focuses on systems using a limited number of high power LEDs. The lumen output of these LEDs is such that even a single red, green and blue LED together can deliver the required lumen output for certain applications. To optimize performance for both luminance and color uniformity we investigated several design options. Ray tracing simulations are compared to the performance of real size prototypes, and recommendations are given for the design of color lighting systems.

Light recycling for light-valve-projection with sparkling video

In recent years, several architectures have been proposed for projection systems with an improved light efficiency by means of color recycling and/or polarization recycling. The recycling of light takes place in a rod integrator where light is coupled in from the lamp through a small hole in an entrance mirror. At the exit of the integrator, light of the wrong polarization state and/or wrong color is reflected back such that, after a round trip in the integrator, the light has a second chance of passing through the exit with a different polarization state or through a different color filter. Besides for recycling light of the wrong color or polarization, the integrator may also be used for recycling the unused light of pixels that are in a dark state. This allows for an increased brightness of bright parts in a dark scene, the so-called sparkling effect known from CRTs. We analyze the combined effects of color, polarization, and dark pixel recycling, extending the models previously proposed by Duelli et al. and by Zwanenburg.