This guest post was written by Marcus Weddle of CADDEDGE.
If you’re a design engineer, you’re probably familiar with LED light pipes. For the rest of us, even if you don’t know the term, these little parts are so common that you’re likely within reach of one right now. Let’s briefly look at what light pipes are and how 3D printing can help designers have more freedom working with them.
LED light pipes (also known as light guides or light tubes) are those little plastic indicator lights on electronics that glow green, white, or red to show things like “power on.” That’s the part you see anyway, but inside is actually a larger piece of clear plastic that routes light from an LED mounted inside the component.
So light pipes are basically long plastic lenses that route LED light to where it’s needed. They give designers more freedom in locating and styling indicator lights, while leaving the LED mounted conveniently to the circuit board—making them very popular components.
A Clear Prototyping Challenge
Prototyping light pipes means testing for physical fit of a part which bridges two different assemblies—the outer casing and a circuit board with an LED. However, the light pipe’s outer shape also
directly dictates how well light will be directed for best optical performance.
These dual requirements mean a functional test will require a highly detailed, optically clear part. Traditionally that means waiting a days or even weeks for a milled part or pattern for molding, and the associated cost which may require approval.
What’s the result of this traditional prototyping process? Designers feel constrained to minimize having to go back for a second revision by designing the safest route—usually not the best ingredient for creating the best design.
Naturally the question arises: Can 3D printing help designers iterate faster and free up their options? Yes it can…using office-friendly Stratasys Objet 3D Printers and VeroClear material.
35 Minutes and Just a Few Dollars
3D printing a typical light pipe takes under an hour with the equipment we used. In fact, for our first simple tests we put several design iterations on the build tray at once and had our parts in 35 minutes. Cost was a few dollars. Our material was VeroClear,
which runs on the Stratasys Objet30 Pro and up (we used an Objet260 Connex 3D Printer
You’ll need to budget some time for post-processing the parts. In addition to a quick support removal step, sanding and polishing for the best optical performance is needed. What’s great about VeroClear is it’s easy to sand and polish and parts have good strength and detail for physical test fits.
Curved light pipe on the left shows poor performance at desired exit surface area; 45-degree flat angle (right) shows a full, even fill of the window. Both parts were 3D printed in VeroClear.
How do the parts perform? We tried the bread-and-butter of light pipes: the 90-degree turn using two designs. According to best practices, a flat 45-degree “reflector” should be used instead of a bend to route the light in the turn. You can see why in the photos—the other part’s curved bend visibly performs poorly compared to the flat angle. But that’s a good indication that the prototype part will bring out design issues in addition to confirming good performance. It was simple to decide which design worked better.
There are several factors that might affect final part performance, but one of the most common is making sure light rays hit reflection features above what’s called critical angle—the angle where light begins to be reflected back inside the part through TIR (total internal reflection). The VeroClear material has a similar index of refraction to the production plastic materials, so it has a similar critical angle too. Our flat 45-degree bend provides TIR and also best reflects the light to hit the exit surface for an even glow.
Predicting Performance on a Production Design
LED light pipe in an enclosure, and its corresponding 3D printed prototype light pipe.
We also 3D printed a real-world production light pipe design, complete with mounting features. As with our simple test, this prototype part shows that even on a longer light pipe, the VeroClear material is ‘acceptable to good’ at predicting the production part performance. While the transmission of light isn’t as high as the production material, we can see that if the 3D printed version is successful, the production material will be even brighter and retain the uniform illumination.
Design engineers take note: the part you see went from CAD to functional testing in about two hours, including printing and post-processing. Part cost was under $5.
With such a fast turnaround, the designer could test and choose the best of multiple designs (we printed four iterations at once), then even revise and print the same day. This rapid iteration cycle allows for more design ideas, and a much higher confidence in the design going forward to the next prototyping stage. As a bonus, the time for these additional iterations is still far shorter than the traditional method.
Multiple light pipes in process of being 3D printed
Clearly LED light pipes are a powerful tool designers use to create better products—both in form and function. Yet the challenges of prototyping these devices can hinder that very freedom by limiting design iterations. Off-the-shelf light pipes might be an option, but for today’s designer that again brings the limitations in the form of conforming to the stock part.
With the speed of Objet 3D Printers from Stratasys and the performance of VeroClear material, you can see how design engineers can drastically reduce the cost and time constraints in functional testing, giving them more freedom in design and, ultimately, creating better products.
A Brighter Future
Today’s LED light pipes are designed to work with mass-produced products, but what about future products that are mostly 3D printed in additive manufacturing? Disney Research
sought to answer just that question (and utilized VeroClear for some incredible light pipe designs) in a project called Printed Optics: