Re: How does Digital Light Processing Work?

(1) OK, before we get started:

There's no way your question sounds stupid. (a) "There are no dumb questions, only dumb answers"; (b) I hold a Bachelor's degree in physics from MIT, and I assure you that no obvious answer popped into my mind!

Digital Light Processing™ (DLP™), it seems, is a fairly new field. Judging by the references listed in the paper below, nearly all the research and development has been done in the last ten years. There's surely not going to be much about it in any standard textbook just yet!

(2) Next, here's a very brief overview for everyone else....

DLP is a way to project a digital video signal to yield a bright, high quality image. The heart of the DLP system is a rectangular array of microscopic mirrors called DMDs, or Digital Micromirror Devices™. Each DMD™ is a square mirror about 16 um (16 microns, or millionths of a meter) on a side, and can flip ten degrees one way (on) or the other (off). The switching is controlled electrostatically, and takes about 2 uS (two microseconds).

The entire array is manufactured in a process similar to that used for CMOS integrated circuits (chips) with the total number of mirrors typically being the same as the number of pixels in standard computer monitor resolutions, such as SVGA (800 x 600) and SXGA (1280 x 1024). Light from a bright lamp is focused onto the mirrors and reflected by them through a projector lens and onto the screen. Color images are obtained through a combination of color filters, one, two, or three DMD chips, and several mirrors and prisms.

Some recent screenings of Star Wars™, Episode II, were shown using DLP.

You can find out more at http://www.dlp.com.

(3) Finally, here's your answer:

I found a white paper (a high-level overview) of DLP on the web at http://www.dlp.com/dlp_technology/images/dynamic/white_papers/14 1_hornbeck.pdf. It goes into a fair amount of theoretical detail, mentioning the ±10 degree angle, but doesn't say anything about a 14 degree theoretical maximum. However, it seems to imply that the larger the angle, the larger the lens must be to provide adequate separation between the light actually desired and the light diffracted from the mirror edges and reflected from the substrate (the substance upon which the mirrors are “mounted”).

Also, as I understand it, the greater the deflection angle, (1) the longer it is exposed to a hot lamp, causing heating and deformation to the mirror's hinge, and (2) the brighter (and hotter) the lamp must be to obtain a high contrast picture.

Finally, the more you bend the hinge, the more mechanical stress it'll experience, and at some angle it won't be able to respond elastically any more. It would become permanently deformed, and would soon break from metal fatigue.

Hope this helps!

Aaron Endelman