LED Light Pipe Design Guide: What You Need to Know About Light Pipes

Ever wondered how lights are transmitted in electronic products? Learn all about light pipe design, the part behind this light transmission.

Leon Huang: Rapid Direct Author

LED Light Pipe Design Guide: What You Need to Know About Light Pipes

Many modern electric products have fancy lights adorning them, with some even having these lights constantly changing colors. Ever wondered how these products transmit this light to their surfaces? It’s our pleasure to introduce you to light pipes, the component that transmits light in these products. Due to these light pipes’ importance, a light pipe design guide is just as important too.

Designing light pipes is not as easy as it sounds in most cases. This is especially true for light pipes that transmit light pipes in complicated environments such as bent products. Such products have to consider complex light pipe design guidelines such as refractive index and the light pipe’s real-world application.

If you’re a design engineer working on a light pipe project, this article contains everything you need to know, ranging from light pipe materials to designing the light pipe itself.

What is a Light Pipe?

Definition

The best way to understand the definition of a light pipe is first to understand its function. A light pipe is a clear tube whose function to relay light from a light source (e.g., LED light) to a user interface (such as the lights present on electronic devices).

Design engineers structure these tubes so that they can relay the light over short distances with optimum efficiency. This means even when they have to move the light around bent corners or tight spaces, they still transport the light with little loss in light intensity. They are the ideal transport source of light in components like printed circuit boards or control panels.

Design engineers also refer to light pipes as “lite pipes or tubular skylights.” There are mainly two types of light pipes, namely: flexible light pipes and rigid light pipes. Rigid light pipes are only meant for transmitting light where the distance between the light source and exit point. Flexible light pipes, on the other hand, can transmit light across longer distances.

diagrams of rigid and flexible light pipe design
Rigid and Flexible Light Pipes

Applications

Light pipes are virtually everywhere, from those small gadgets such as your gaming consoles to bigger equipment such as those lights on ATM buttons. While we can go on about different devices that utilize light pipes, let’s explain some principles that actually guide light pipes’ applications.

1.      Bending Light

One thing common to most devices using light pipes is that they don’t usually have straight shapes. These devices have their light sources (LEDs) located in a secluded location away from the point where the light is actually needed. This means the design engineer has to use LED light design guides to include a light pipe in the gadget or part. The light pipes are responsible for the transportation of light in such bent gadgets. This is possible as long as light transport obeys the laws of physics. Flexible light pipes seem like the perfect fit for this project. However, some rigid pipes might also work.

2.      Lengthening Light’s Reach

One disadvantageous characteristic of LED lights is that they consume a lot of power. This means using a lot of them in a gadget or part could be quite consumer-unfriendly. An alternative to using many of these LED lights is including LED light pipe design guides in the gadget plan. Light pipes will help extend the light source’s reach, thereby eliminating the use of many LED lights.

We’ll consider some typical examples of these two applications in the case study section.

A few fields where design engineers apply light pipes include:

  • The aviation industry, e.g., Personal jetpacks
  • Sound and Communications Industry, e.g., Sound decks.
sound decks using light pipes
  • Medical Industry, e.g., MRI machines.
  • Network and Internet Service Providers, e.g., Routers.
routers using light pipes

Materials

Choosing the light pipe material is one of the most important decisions every design engineer has to make when making a light pipe design. The material will determine if the light pipe will withstand its real-life function. Hence, when deciding the material to use for a light pipe design, the first thing to consider is its end-life function. To sort this out, you can set a guideline of questions such as:

  • Is the product meant for in-dash electronic systems (such as car stereos) or a consumer system (such as a refrigerator)?
  • Is the product meant for industrial use or for use in the medical industry?

Answering these questions will give an initial sense of direction as to which material will fit the product. Some other factors that you can consider when picking materials:

  • The vibration frequency and water-resistance of the finished product.
  • The tendency of the finished product to catch fire.
  • The operating temperature range of the finished product.
  • If the product will have any ultraviolet (UV) or infrared radiation (IR) needs.

In the materials themselves, design engineers recommend various materials in the light pipe design guide, ranging from plastic, chemicals to even glass. We can list out various materials popularly used in light pipe design, namely: PMMA (Acrylic), Polycarbonate, Zeonex, PMMI, and Silicone resins. There’s a table comparing the characteristics of these five materials below.

While these five materials all have seen considerable use in the industry, acrylic and polycarbonate are standout materials due to their desirable set of properties. Let’s take a deeper look into each of these two materials:

1.      Acrylic

acrylic sheets
Acrylic

PMMA (Polymethylmethacrylate), also known as acrylic, is a transparent thermoplastic best known for its optical properties. Acrylic transmits 92% of the light that passes through it, which is higher than that of any other light pipe material. Apart from this, it is popular for its stability under UV light exposure. This factor optimizes it for outdoor uses and in UV-light-prone areas.

Also, it is easy to dye and keeps its color intact even under UV light exposure. Its most attractive characteristic (especially to clients) would be its relatively economical price. Compared to other light pipe materials, acrylic is cheaper. However, it is not all rosy for acrylic as a light guide material. In terms of durability and heat resistance, it is not as good.

2.      Polycarbonate

polycarbonate sheets
Polycarbonate

Where acrylic is poor, polycarbonate stands tall. Polycarbonate is a type of amorphous thermoplastic renowned for its high-temperature resistance and durability. Polycarbonate has ten times the strength possessed by acrylic, making it suitable for heavy-duty operations. It also possesses a low tendency to catch fire, making it useful for products that tend to heat up. Similar to acrylic, it is also UV stable and has excellent light-transmitting properties.

Analysis of Real-Life Products Utilizing Light Pipes

This section analyzes some real-life products that have optimal use of light pipes in their operations. Examples of such product include:

  1. Tivo Bolt Status Lights
tivo's only logo light
Tivo’s sole logo light

For those who don’t know, Tivo Bolt is a media box for recording media content. This media equipment utilizes light pipes in five different light spots on the box. For all of these spots, the light source was bent through the light pipes for the light to reach the exit point. The single light present on the Tivo logo uses a clear polycarbonate tube as its light pipe, which is only slightly bent from the light source to the exit point.

tivo's four light design
Tivo’s four lights

The other four lights, placed side-by-side, uses a multiple-unit light pipe, with each having its light source, entry points, and exit points.

tivo's four light pipes design
Tivo’s four light pipes

The manufacturer then makes a brilliant counter against light leakage by covering all the light pipes with black plastic. This makes each light stand out distinctly.

tivo two black plastic covering
Two black plastic covering

This product is a good example of the light-bending principle explained earlier.

  • The Well-Lit Thumb Pad of Logitech G600 MMO Mouse
logitech gaming mouse
Logitech C600 MMO Gaming Mouse

The Logitech C600 MMO mouse is a gaming mouse with 12 thumb buttons on the side. Each of these buttons has customizable backlights. Now take a wild guess at how many LED lights to power these twelve buttons? No, the answer isn’t twelve. It’s just two! You’ll agree with us that that is just amazing.

The manufacturer achieved this by placing side-firing LEDs that transmit their light into a flat-plate light pipe. This light pipe runs through to all the buttons, thereby providing light to each one. However, they ensured the LED light source was not too far from the entry points. This is to minimize the loss of light as it had to travel a long distance.

logitech parts
Logitech parts

Also, the elastomer thumb pad on the opposite plastic pad has some black spots on some keys. We suspect this is an effort to mask the hot spots so the light can spread around evenly. The white and super polished top and bottom surfaces of the light pipe plate are all in an effort to improve color mixing and maximize total internal reflection.

This product is a good example of the “lengthening the light’s reach” application.

Factors to Consider When Designing a Light Pipe

Designing a light pipe could be a very easy task if you know the right guides to follow. First, there are some general rules that you must always consider in light pipe design guidelines. They include:

1.      Minimize loss of light

The first rule is to always try to minimize light loss as much as possible. The design must always ensure optimum transmission of light. The best way to achieve this is by making sure the distance between the light source and the exit point is as short as possible.

2.      Consider some questions

One sure way of always checking if your light pipe design guidelines are on the right track is making a checklist of questions. Ticking off each of these questions will help put a sense of direction to your light pipe design. Examples of such questions include:

  • What is the light source coming from?
  • How much light brightness do you need?
  • Can your design optimize light transmission?
  • What is the distance between the source and the exit point?

Questions like this would help you to put tracks on how close your design is to become a success.

3.      Rigid or Flexible Pipes?

Knowing the right type of pipe to use for your design is another important characteristic to consider making a light pipe design. As a rule of thumb, design engineers recommend rigid pipes for short distances between light sources and exit points, while flexible pipes do the direct opposite. Also, flexible pipes are more eligible in bent, shaped parts, while rigid pipes can only be used in straight or right-angled situations.

4.      Refraction

refraction in acrylic
Refraction

This term is used to describe the change in the direction of a wave (in this case, light) when it moves from one medium to another. The refractive index of acrylic is 1.49. Design engineers have to take the refractive index into consideration when making their light design guides. This is because they are important for the optimum transmission of light through these light pipes.

5.      Total Internal Refraction (TIR)

explanation of total internal refraction
Total Internal Refraction

This term describes the angle at which light bounces off from one surface to another without refracting to a surface exit. This phenomenon occurs when the incidence angle of the source of light is greater than a certain limiting angle known as the critical angle. Knowing the critical angle of various materials is very important as it helps to ensure the transmission of light with maximum effectiveness.

explanation of total internal reflection
Total Internal Reflection and Critical Angle

Conclusion

If your products contain LED lights, using light pipes is the best way to get the light evenly spread out in your product. However, there are a lot of factors that go into making this successful. Handling it all alone could be very tedious for you.

This is why you need a company like RapidDirect to help you handle all your light pipe design projects. At RapidDirect, we understand every factor that we need to consider before creating a light pipe design. We also know the suitable material for every project and how to make your light pipe project a success.

With our rich base of expertise and experience in LED light pipe design guides, we make suggestions to improve your design to the best. We also make multiple prototypes to ensure we have a functional prototype that brings your ideas to life before commencing mass production. After manufacturing, we also offer quality inspection and material certifications just to assure you of the highest quality of manufacturing possible. You’ll get all of these at the best price ever.

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