How to Convert a Digital Watch to a Negative Display

According to the time difference in the before an after shots, it looks like this takes ~4 hours to do?

It's actually really simple. The display works in a way that you control the polarization of outgoing light (but the intensity is constant). Then you filter whichever polarization you want. So a black dot on a white screen could be achieved with a small vertical polarization region on a horizontal pol. background, and filter out the vertical pol., with a polarizer horizontally aligned. Align it vertically, and you swap the intensities.

Note: In this case the light whose polarization is controlled is the reflected incoming ambient light, which isn't polarized; in a computer monitor it's the back light.

Inkjet transparency sheets like you'd find at your local office supply store [0] are polarized; you may not have to order polarizing film.

I used to own a car that had an LCD display where the orientation of the polarization was perfectly set so if I was wearing my polarized sunglasses, the screen was blank. I cut out a little overlay made out of an overhead transparency and fixed the problem.

0: http://www.officemax.com/office-supplies/presentation-equipm...

> It took me a little over four hours to do this, but nearly three of those were spent trying to replace the glass display that I shouldn’t have removed in the first place. There were also some other distractions along the way.

Nice. I remember doing this to my scientific calculator at school.

Modern colour LCDs are still polarised, so I can only view my phone and tablet in one orientation when wearing my polarised sunglasses. On the plus side, they make for an excellent real life ad-block to those annoying video billboards (which are just portrait LCD TVs).

I wonder how practical it would be to make a private display by removing the polarising film from it and then viewing with polarised glasses.