SLA 3D Printed Light Pipes

What are Light Pipes?

3d printed light pipes (also called light tubes) are components that are used to redirect light from its source to a desired location. Some of the most popular applications for light pipes include vehicles and electrical instruments where they are used to illuminate indicators such as the dashboard on your car or backlight displays such as the letters on your keyboard. Other applications include Solid-state lighting, where light pipes are used as mixers to create a wide range of colors from various multi-colored LEDs, and projectors, where light pipes are used to create an even light distribution.

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How are Light Pipes made?

Light pipes can be made one of two ways, either as a mirrored tube with a hollow center, or as a transparent solid material. The hollowed designs require reflective walls to maximize the input light, while solid material designs rely on total internal reflection. The main cause of light loss in solid transparent designs is due to reflection loss at the input (start) face and at the output (end) face. Hollow designs, on the other hand, are at a higher risk of light loss due to absorption on reflection. Since solid, clear materials offer less light loss, that is what we will focus on, and this is where SLA 3D Printing comes into play. Though production level light pipes will be more cost effective to do with industrial processes such as urethane casting, prototyping light pipes will be far more cost effective to do with 3D printing, as it has no overhead for tooling and allows for as many CAD changes as necessary before deciding on the final design.

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How to Design for 3D Printed Light Pipes

When designing a light pipe, it is important to consider your application first. In most cases, the goal is to take light from your source and redirect it to a desired location, and in doing so, you want the maximum amount of light to be captured as possible. In order to do this, a few basic principles should always be in place.

• Make sure you are capturing as much input light as possible:
  • One of the easiest and cheapest ways to do this is by encapsulating your LED (or whatever your light source may be) within the input face of your light pipe.
• Make sure that your light pipe is as reflective as possible:
  • Though this will not come into play as much until the material and post processing methods are chosen, designing the pipe in a way that will limit light loss is a great way to accomplish this. For example, on a light pipe using a 90° bend, adding a 45° chamfer to the face opposing your light source will result in a better and stronger exit light.
• Add abrasion to your exit surface:
  • By doing this, you are creating a select surface with very low internal reflection which will allow the light to escape at the point of your choosing.
    • This can be done by printing a texture on this face of the part
    • It can also be achieved by masking off the rest of the part except for the face that needs this finish and bead blasting it to give it a matte finish.
• Understand 3DP light pipes limitations:
  • Due to the layer based process used to print the part it will transmit around 30%-50% less light then a molded or machined light pipe. Most likely your final production light pipe will be brighter then the ones you prototype with 3D Printing.

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Best Materials for 3D Printed light pipes

Since we are looking for materials with the highest amount of internal reflection, we can immediately exclude any material that is not clear, which leaves us with 3D Printed SLA Accura Clearvue. This material offers the closest level of clarity to optically clear as possible and will not cost an arm and a leg to use. As for post processing, there are a few options available, however for this application, a polished clearcoat will be the most suited for the best possible outcome.

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