Prototyping Light Pipes For Circuit Boards
If you’re designing a product that has a space between the product casing and an internal circuit board with an attached light — but you’re trying to get the light to reach the outside of the casing — then you may need a light pipe.
Light pipes are essentially what they sound like: tubes or pipes that transfer light from one location to another.
They’re commonly used when a circuit board-mounted LED is situated perpendicularly to the side of the product that the light should reach. Large companies often produce thousands of light pipes for their own products with this design issue, but you might find that you only need one or two with specific size and shape requirements.
Though it may seem challenging at first to find a solution, there is a light at the end of the tunnel: you can make pipes that will fit your product.
The CAD engineers at Jaycon Systems have found that the most optimal way to create a customized light pipe is to use a high-quality 3D printer and clear material. Depending on your circumstances and access to equipment, however, completing a project with these items may or may not be feasible. As you’ll learn below, there is an alternative method using 3D-printed pipe models and resin casting that anyone with access to a 3D printer can perform.
How light pipes work — the basics
A large light pipe, such as the kind used in a home or commercial building to bring light from the roof to the interior part of the structure, typically has a hollow tube with a reflective coating that allows light to bounce off the walls until it exits the other end of the tube.
Small light pipes installed in electronics products, on the other hand, are simply solid structures that are free of any internal defects. Smaller pipes also tend to have smooth surfaces that allow light to travel along the inside without escaping the pipe.
Making your own light pipes
If you don’t have access to a 3D printer that can produce virtually blemish-free transparent items, then you can achieve the desired results by designing and printing one or more light pipes in whatever material is available, sanding the printed pipes as smoothly as possible, then creating a Room-Temperature-Vulcanization (RTV) silicone mold and pouring clear resin into the mold to create transparent light pipes.
Here’s how to do it:
1. Create or obtain pipe designs
You can get CAD files free online from any number of sources, but because there are hundreds of thousands of existing models, and because every product needs a different shape and size, you’ll probably need to make some variations of the original design in order to get the right fit.
We started with designs from a parts distributor that happened to have an online CAD file of the pipes they sell, then made variations using CAD software by SolidWorks. We started with a standard light pipe that was short and straight and made two variations of that pipe. Both variations had 90-degree angles; one with a smaller, tighter radius and the other with a larger, looser radius. We also found a circuit board-mounted light pipe that directed the light at a 90-degree angle through a flat and sharp turn. We made another design like this, but with a curved back so it would better emit light.
2. Print models of the pipes
For the second step, you’ll bring the items from digital files into physical form by 3D printing the parts using any solid color material. We chose white. These models will be used to create the mold, so don’t forget to sand the surfaces of the models after printing.
3. Make a mold of the pipes
To make clear copies of the solid color pipe models, you’ll have to make a silicone mold. To do this, and to carry out the next step, you’ll need modeling clay, silicone rubber, cups for mixing, clear casting resin, mold release, popsicle sticks, a razor blade, rubber bands, tweezers, a chipboard, masking tape, small paint brushes, a rolling pin, foam board and a ruler. Click here for pictures and directions on how to make the mold.
If you’re making multiple pipes, you can either create one mold, or separate molds for each pipe.
4. Create the light pipes with clear resin
Once the mold is ready, use these directions again to form the light pipes with clear resin. Cut and sand any excess material left on the finished products.
5. Paint the light pipes if needed
We painted the pipes black at first but found that this actually made them emit less light. We then removed the black paint and painted the pipes with a metallic paint, which worked as well as the unpainted light pipes but added a ring of intense light from the light pipe. You may find this to be unsatisfactory in some instances.
Tips that can help you improve the process
Use a straight light pipe whenever possible in order to obtain maximum light transfer. If you find that a bend is necessary, a gradual bend is better. Sharp bends do not emit light as well as curved bends.
Smooth out the 3D-printed parts as much as possible before making the mold. Any roughness around the length of the light pipe will allow a significant amount of light to escape.
Use a pressure pot to minimize or eliminate bubbles in the finished pieces.
Know that regardless of how well you follow all the steps, your light pipes may leak light from the sides. This happens inside the housing and usually is not a problem. If this creates issues with the ambient light, however, the light pipe bodies can be painted to reduce the amount of leaked light. Keep in mind that light pipes tend not to perform as well when painted. If painting the pipe is necessary, do not paint where the light is meant to enter and exit. Choose a reflective paint that will help the light reflect inside the pipe, not a dark paint that will hinder the ability of the light to travel.
This article was published by the Jaycon team. Learn more about how we can take your product design and hardware idea to the next level here.