One of our challenges when building the first 150 beta units of alima was to avoid tooling to save time and money. On the other hand, we also valued a lot how the light was managed and spread out in the product.
There’re two things to take into consideration when you want to use LEDs as an output in a product:
First light can only shine at a right angle of the PCB; or alongside with the electronic board if you use 90° type of SMT LEDs. In case you want to reach a location of your product which isn’t directly aligned with the board you will have to buy, or have made, a LED pipe that will conduct the light to the right place.
Here are some examples or ready made led pipes:
The second role of a led pipe is to act as a diffuser; i.e.: the light is guided with minimum loss and, at the end, spread equally on the surface of the casing. This is accomplished by polishing the end of the pipe as you may see on above pictures.
In our case we wanted the light to be visible from all angles and spread out equally over 360° horizontally. To achieve a light ring usually you design a circular PCB with many LEDs and you have a diffuser right in contact with them.
See ring diffuser (showed in the hands of the person) and circular PCB with lots of LEDs (at the back):
Credit: ifixit.com teardown of google nexus Q
We couldn’t afford to have a special LED board so we had to have the LEDs on our vertical PCB. Also we couldn’t afford to have a ring piece that we would need to polish by hand.
So we had to conduct the light as equally as possible to the edges and then to diffuse it. For both functions we used light reflection by having a kind of gear teeth pattern laser cut in our transparent pmma. We tested several design and found out that it was by having one gear pattern close to the LEDs and one at the edge that it work out the best to have a relatively equal spread of lighting.
Several tested patterns:
Best working patterns:
The second part of the solution was to choose through hole diffuser LEDs so we could have two equal one on each side (only one side of our PCB uses SMTs) and they could also spread light toward the top of the enclosure.
Here with a transparent bottom plate, so you can see the inside:
Here how the led are placed on the PCB:
And now the results, having diffusing LEDs and reflector allows the light to spread vertically just as we wanted: