Sunday, March 8, 2015

How Digital Light Processing (DLP) works

Digital Light Processing projectors use a chip that is covered with tiny mirrors that tilt back and forth. When the mirror is tilted one way, it reflects light out through the front of the projector, creating a bright pixel. When the mirror is tilted the other way, the pixel is dark. In this video, I explain how DLP works and show a macro-scale model.


  1. So why don't they put colour wheels in LCD projectors or alternatively have 3 light paths in DLP projectors?

    1. Some LCD projectors do have colorwheels, but in general, LCD is too slow for this to work. A DMD can flip a mirror in 5 microseconds, but an LCD requires about 5 milliseconds (or more) to change state. Liquid Crystal on Silicon (LCoS) can be faster, and is more often used with sequential color-cycling technologies, but often is not used on higher-end projectors because the image quality isn't as good.

  2. Good video as always :) I really appreciate the short length of these videos, you don't have to think that if you got time to watch a 10 minute video, you can just do it.

    I wonder if it would be possible to make a PCB with tracks that act as coils to drive the matrix.

  3. Imagine if the individual mirrors could have 4 stable states rather than being just bi-stable. If the mirrors had staggered rotor/stator points on the back and the processor could place each mirror in one of four positions, you might have a prism in front of the light source and the mirrors position could present the light at one of four points in the spectrum (4 positions - including no light reflection). Red, Green or Blue or Off... or whatever arrangement of color in the spectrum best suits the application. Or even more impressive, 128 or 256 state positioning, imagine the speed and color diversity. Exciting!

  4. Would it not be possible to use a fixed RGB filter array in the light path of the chip, rather than using a spinning color wheel?

  5. Ben, you could have mentioned: A big problem in LCD displays is that when the pixel is off, the light is absorbed in the LCD. This heats up the LCD. And once that goes above a certain temperature, the Liquid Crystal simply becomes Liquid.... no more crystal, no more display.... So cooling the LCD is a problem (both sides have light passing through: the cooling system needs to be transparent!) whereas the light dump in a DLP can simply be a black blob of aluminum.

  6. How are dead pixels handled - does one bad mirror ruin the whole thing or is there an algorithmic compensation?