Here is a new Microvision patent that describes how to use LEDs instead of lasers to make a scanned display. They use a row of multiple repeating combinations of 1 red, 2 green and 1 blue surface emitting LEDs and then scan the row in a raster pattern to form the image. This requires that the row of LEDs form parts of the image that overlap and this is explained. In this patent SELEDs, surface emmiting LEDs, are used, as opposed to EELEDs.
United States Patent 7,486,255
Brown , et al. February 3, 2009
Scanned beam system and method using a plurality of display zones
Abstract
A scan assembly includes an emitter array containing a plurality of optical emitters. Each optical emitter generates a corresponding image beam and the scan assembly scans the image beams in a plurality of overlapping display zones. The overlap of adjacent image display zones forms blending zones and the scan assembly can modulate the intensities of the image beams as a function of the position of the image beams in the blending zones. This modulation for a given blending zone may be a linearly increasing intensity of a first image beam and a linearly decreasing intensity of a second image beam.
In the text it explains why SELEDs are used
“While the beam generator 16 can be formed from lasers, laser diodes, LEDs, or other suitable light sources, cost and operational characteristics may make one or more of type of light source more or less attractive depending upon the application of the image-display system 10. For example, lasers provide high intensity light for the optical beam 18, which will generate a bright image, but may be relatively expensive and require external modulation. Laser diodes can provide a high intensity optical beam 18 at a relatively low cost compared to other types of lasers. Although costing substantially less than other types of lasers, however, laser diodes are still relatively expensive.
In contrast to lasers and laser diodes, LEDs are relatively inexpensive and therefore from a cost perspective are ideally suited for applications where the overall cost of the image-display system 10 is a primary consideration. There are several different types of LEDs, with some LEDs being more specifically referred to as surface emitting LEDs (SELEDs), meaning that light is emitted perpendicular to an active region of the LED surface. The use of SELEDs, which may be referred to simply as LEDs in the present description, may be limited in the image-display system 10 for some applications due to the relatively low intensity of generated light, resulting in a low intensity optical beam 18 and an image that is not as bright as desired. For example, if the beam generator 16 were to be formed from a red, a blue, and a green SELED, the resulting image on the screen 14 may not be as bright as desired.
Many current image-display systems 10 utilize either lasers or laser diodes to generate sufficiently bright images. While lasers provide a required intensity of light, they may be relatively expensive, undesirably increasing the overall cost of the system 10.
Another type of LED known as an edge emitting LED (EELED) emits much higher intensity light from between the heterogeneous layers in the device and thus would be well-suited to use in the beam generator 16, but such EELEDs may adversely affect cost and availability of systems constructed with them.”
http://tinyurl.com/bv6zhh
