AIM Processing Small Plastic Parts Blog

Light pipes are rigid, transparent plastic shapes that transfer the light from a light-emitting diode (LED) within an electronic enclosure to the outside. They serve many purposes, including letting  the user of a device know whether it is on or off, whether its battery is in need of charging, etc. Light pipes can transmit as much as 80 percent of the light emitted by an LED mounted on a printed circuit board, making them a great way to share the status provided by an internal component while keeping that component safely enclosed. They can also be used for decorative purposes like illuminating a product logo.

There are complex physics that go into designing a light pipe so that it retains as much of the light as possible as it travels—things like Snell’s Law, Fresnel Loss, etc.—but we won’t go into that here. Suffice it to say, the simple little red or green light you see on an electronic device is not always as simple as it seems. Luckily for you, plastic injection molding experts like our team have an in-depth understanding of light pipes, allowing customers to just enjoy the end result.

Light Pipe Options

Light pipes can be created with polycarbonate or other optical grade materials, and can be compatible with either through-hole or surface-mounted LEDs. They come in two general formats: vertical and right angle. There are single and multiple units, and designs can use a variety of shapes including round and rectangular.

Choosing the right light pipe for your project requires answering some key questions:

• Where is the light source?
• How far from the emitting source is the LED?
• How much brightness do you need?
• What type of LED is being used?
• What path is available from the LED to the emitting source?
• What mounting options are available?

With these answers in hand, you can proceed to creating your design.

Designing for Optimal Light Emission

In order to transfer the maximum amount of light from the LED to the exterior of an enclosure, you should follow these light pipe design best practices:

• Use wide arcs and gradual bends rather than sharp corners
• Use scattering surfaces or frosted texture where appropriate to diffuse the light, if you wish
• Consider the effect on your design of the many available light pipe shapes
• Use ray tracing software and do enough modeling to be confident in your design
• Optimize the coupling of the LED and the light pipe
• Ensure nothing impedes the escape of light from the pipe’s external end

Containment

With the intensity of LEDs, the light from one LED or its light pipe can often travel through freespace to an adjacent light pipe.  For example, if you have persistent illumination of a "Power On" LED, that light could leak into an adjacent "Ready" indicator.  This can cause confusion for your user about the true state of the device.  A common way to prevent this is through an opaque shroud, either plastic or some other masking material, which will deliver crisp indicators to your customer.

Let’s Have an Illuminating Conversation

If you’ve got questions about light pipes and electronic enclosures, we’re happy to share the expertise we’ve accumulated in our more than two decades in business. Give us a call.