LED based projectors have numerous advantages compared to traditional projectors: they are more compact, exhibit a larger color gamut and a longer lifetime, the supply voltage is lower, the absence of ultra violet, infrared radiation and mercury vapour, etc. Furthermore LED's can switch on and off very rapidly (possibility to pulse them) and they have a high dimming ratio that can be used to improve the contrast. However, there is also an important disadvantage: the optical power per unit of etendue (luminance) of an LED is significantly lower than that of e.g. an UHP-lamp. Because of this and the etendue limitation of the projector (small light valve, f-number projection lens), the projected flux on the screen will not be high. Despite this shortcoming, LED's are still very interesting for low power applications because of their superior properties. However we have to collect the available light flux optimally and combine multiple LED's with high luminance within the available system etendue. In this paper we have studied collection optics that collect the LED flux with high optical efficiency and collimation and reshape the spot in a uniform illuminated rectangle with the sizes of the micro display. We have designed 'Gradually Tapered Light Pipes', 'Elliptical Reflectors' and 'Parabolic Reflectors'. Furthermore we have combined many of these LED/collector combinations to get a high luminance illumination engine for LED based projectors.