Light pipes are a lot more common than you may think. Many products in your own home with an LED in them are likely to have a light pipe inside. (Yes, this includes your Amazon Alexa or Google Home). But what are they? How do they work? This article will dive into the ins and outs of light pipes and what you should consider when using or designing them.
What is a Light Pipe?
Light pipes are like PVC pipes, but instead of transporting water and other liquids, it transports light from one point to another. They are like tunnels, guiding light where it needs to go, transmitting through the inside of the light pipe by reflecting on its internal surface until it reaches the surface of where the light will be visible.
The first step in understanding how light pipes work is to understand the basics of light refraction, as it is the foundation to building effective light pipes.
When rays of light pass from one medium to another (for example: from water to air), those rays change direction. Once the rays of light pass through another medium, they will either leave the medium with a new angle or reflect into the original medium.
How does this relate to light pipes? In essence, the light pipe is trapping the rays of light through total internal reflection (shown in the diagram below) until the light reaches the pipe’s end and can exit. Usually, the light pipe will go from the light source in the circuit board to the area that requires illumination. Some products you are probably familiar with that use light pipes are modems and routers, drones, robotic vacuum cleaners, and smart headphones.
As you can see from the diagram below, the light pipe also acts as a light diffuser. The diffuser helps the rays of light exit the light pipe at the desired location to ensure more uniform illumination.
How Are Light Pipes Used?
Light pipes are everywhere in technology, from security and communications equipment to medical devices and even toys. To be more specific, they’re in most pieces of technology that have LEDs as status indicators.
Why Are Light Pipes Useful?
In product design, light pipes are specifically useful when you have a light source at one point of your product but want the output elsewhere. Light pipes can transmit up to 80% of the amount of light that goes through them, making them a great option if an LED’s placement in a circuit board does not line up with its casing. They are handy because they provide flexibility in the product’s design while offering ease of installation during assembly. They are also affordable and allow for uniform diffusion of light from their original source.
What to Consider When Choosing the Type of Light Pipe
There are a variety of different types of light pipes; short/long, rigid/flexible. Your choice should mainly depend on your project/product. If your light source is near the desired output location, you will be better off with a short-rigid pipe. Whereas if your light source is on the opposite side of the desired output, you should use a long-flexible pipe, considering it will need to go around obstacles.
Size & Angle
When adding a light pipe to your product’s design, the recommended distance between the LED and the light pipe should be less than 1.27 mm/0.05 inches. Its viewing angle of the LED should be 160 degrees or less. Combining the narrow viewing angle + the LED’s proximity will maximize the amount of light going through the light pipe. In other words, it helps minimize the amount of light loss, as shown in the diagram below.
Design Features
The image below shows a 3D model of what we call a light pipe array design. This type of design guides multiple LEDs that are close in proximity. Instead of installing three different light pipes to the design, only one light pipe is used, reducing the number of parts needed, the cost, and the assembly time.
This next design feature helps guide LEDs that are perpendicular to the desired output. It includes an angle of 45° in which the light bounces and gets redirected. As you see from the diagram below, light enters from the underside going up until it reflects on the angled surface and redirects towards the exit, where it leaves the light pipe.
The last design feature is called an LED cavity. Considering the LEDs’ position and the desired output, having a cavity is better than having a complete solid pipe because it helps reduce light loss. The light loss is minimized because there is less space between the LED and the pipe.
Light pipes are highly customizable, making them a great tool when designing your product. Regardless of your product application, Jaycon can help you select the perfect off-the-shelf light pipe to fit your design, or we can help you design a completely new one to better meet your needs.
Originally published at https://jayconsystems.com on February 9, 2021.
