Polarizer Clock

This clock does not use any colored LEDs instead the colors result from the effects of polarization.

The clock face is edge illuminated by white LEDs this light than passes a linear polarizer. After that it passes a transparent polycarbonate (PC) plate which exhibits stress-induced birefringence and thereafter a second polarizer. The colors appear because the PC plate rotates the polarization and the amount of rotation is dependent on the wavelength. Because the second polarizer is rotating, the clockface is constantly changing its color.

1. 170mm diameter, 2mm thick PC plate
2. 170mm diameter, 3mm thick translucent acrylic plate
3. clock components kit 011
4. 2pcs polarizer foil with adhesive backing 200x200mm
5. 1m, 3mm white LED strip with DC jack
6. transparent book wrapping foil (or Tesa tape)
7. reflective window film / mirror film
8. 3D printer
9. cutting plotter

At the beggining I had different ideas on how to make a clock out of polarizers. The final project is the result of experimenting with different designs and materials. For that I build myself a small lightbox ordered linear film polarizers and a bunch of potentially interesting (birefringent) materials.

One of the first ideas was to cut numbers out of polarizing film at different angles between 0-90° and then have a second polarizer rotating in front so that the numbers fade from light to dark one-by-one. However, it turned out that the contrast between the numbers is too low if you start having more than about five of them.

Anyway, I wanted to make something colorful and remembered the nice colors that result from stress-induced birefringence. After some research on the web, I identified polycarbonate, Tesa tape and cellophane as interesting materials and got hold of some samples. After some experimenting I settled on the design where I would have a fixed polarizer followed by a PC plate and a second rotating polarizer.

I chose this specific clock kit because it has a "creeping second" and because there were already existing stl models for the clock hands and clock holder including a modular stand. I had to make some minor modifications to the clock holder and clock stand. Unfortunately, the original license on makerworld does not allow me to publish my modified models here. I reached out to the original author if he could grant me the license to publish my modified files.

I also designed holders for the LED strip and the rotating polarizer. These stl files can be found on my github.

All parts were printed from white PLA except for the clock hands that were printed from transparent PLA.

The first polarizer was attached to one side of the translucent acrylic plate and the excess foil was removed with an exacto knife. I also marked the orientation of the polarizer on the side of the plate so that it can be aligned correctly later. On the backside of the plate the mirror film was attached.

Note that the plate has an 8mm diameter hole in the center for the clock shaft.

For the dial I chose a "spiral" or "infinity" pattern which was designed in inkscape. Originally, I wanted to cut it from Tesa tape or cellophane with my plotter and have only the numbers and the indicators transferred to the PC plate. However, the design was just to delicate in order to cut and transfer it in one piece. Therefore, the clock dial was cut from book wrapping foil, the numbers and indicators were removed and the remaining piece was attached to the back of the PC plate. You can find the dxf file on my github, do not forget to mirror it before cutting.

Note that the plate has an 8mm diameter hole in the center for the clock shaft.

The second polarizer was cut to shape with the plotter. It contains a 3.5mm hole at the center where I attached the holder for the seconds dial. This holder was removed from the original dial that came with the clock kit and then attached to the polarizer using superglue. Since the polarizer also has an adhesive backing I attached it to an 0.2mm transparent PVC foil. If you use non-adhesive polarizer film it might not be necessary although it also gave the polarizer film some extra stability. The polarizer film is then placed in the 3D printed ring which consists of two parts that snap fit together and can optionally be fixed with superglue.

The acrylic plate with the polarizer is edge illuminated by the white LED strip. The LED strip was attached to the 3D printed LED holder ring and then placed around the acrylic plate. Then the PC plate with clock dial was added on top. It is necessary to align the PC plate to the polarizer in a specific angle in order to get the maximum color contrast. Care has to be taken that also the power cable for the LED ring is located at the right position in the lower right corner so that it later fits inside the clock stand. After everything is aligned, the top part of the 3D printed holder ring was placed onto the PC plate and fixed with superglue.

Then the clock holder is attached to the clock stand using the 3D printed screw. The dial is attached to the clock and fixed with the included bolt.The cable was fixed on the clock stand with a self-adhesive cable holder.

After that the 3D printed minute and hour hands can be added and finally the second polarizer needs to be carefully attached to the shaft.

I spent way more time on this project than I originally anticipated to get all the details right. Overall I really like the slick design (also thanks to the clock holder by Motiform) and the colors are even more beautiful in real life. Another interesting effect I noticed is that the colors are different close to the LEDs because the heat changes the stresses inside the PC plate. However, there are always some things that can be improved.

The contrast of the numbers on the dial is not that great so it might be worth to use Tesa tape instead on the book wrapping foil after all. One could also think about using laser cutting to to remove parts of the PC plate. In this case the dial would constantly fade from light to dark.

The rotating polarizer at the front is very delicately attached to the clock shaft. It might be useful to add some support structure to the LED ring to hold it in place.

Instead of 3D printing the clock hands could be lasercut from PC in order to make them also change color.

The edge illumination can certainly be improved as the light is noticably dimmer at the center. One might also remove the LEDs completely and have the clock illuminated from the back by sunlight, although part will be blocked by the clock module.