A light pipe is a solid transparent plastic rod, or an optical fiber used for transmitting light. The non-conductive light path requires no solder or crimped terminations and eliminates the potential of electrical shorts due to pinched wires; no solder or crimp terminations are needed. A light pipe offers several benefits, including clean status indication and simpler human factors engineering. Light pipes are critical components in many modern electronics applications.
The most common categories of LED light pipes are rigid pipes and flexible pipes. The two types offer you a distinct choice for your design. But which one to choose? Like many decisions in life, it depends on what you’re looking for. Here’s a quick rundown of the key facts to help you out.
Rigid Light Pipes
Figure 2: Rigid light pipes are available in numerous configurations, including models with integrated LEDs
A rigid light pipe is designed to carry light shorter distances in moderate to high vibration conditions and in damp or dusty environments. Rigid light pipes are available in many configurations including vertical, right angle and multi-levels and are designed for distances up to 3 inches. A rigid light pipe is constructed from polycarbonate, a material with several desirable properties. It is highly transparent; it has high impact resistance; it is durable and has high heat resistance, making it suitable for high-temperature environments. It is also non-flammable.
Rigid light pipes are available in numerous configurations (figure 2), including straight, right angle, single-unit, or multiple-unit, stacked or vertical arrangements Rigid light pipes with an IP67-rated heavy-duty threaded retention provide maximum protection against liquid and dust incursion. Complete solutions are available that include the light pipe, the LED, and a surface-mount adapter.
Overall, rigid light pipes are an economical way to move light from an LED to the indication area on the front panel when direct access is available.
Flexible Light Pipes
A flexible light pipe is preferred when light must be moved over longer distances or around obstacles between the LED and a front panel or other display location. A flexible light pipe assembly consists of an adapter, which provides less light bleed, and a flexible optical fiber with a lens cap. Flexible light pipes are immune to electromagnetic interference (EMI) and do not conduct or transfer electrostatic discharge (ESD) pulses.
Figure 3: A flexible light pipe system has several constituent parts
Flexible light pipes are more complex and cost more than rigid light pipes; they solve accessibility challenges for engineers by giving them the flexibility to bypass components on the printed circuit board (PCB) that prevent a straight-line access to the indication area on the front panel.
Figure 3 shows the various parts of a flexible light pipe design. The components consist of the LED at point A; a Zero Light Bleed ™ (ZLB) adapter that ensures no light bleeds into an adjacent pipe; a plastic optical fiber (POF); and a lens cap at point B that is bonded to the POF.
Flexible light pipes make it easy to add additional indicators or replace a damaged assembly because the lens cap at point B can be up to 330 feet from the LED light source at point A. The light pipe and lens need far less room near the panel face than the LED and its circuitry. If a human-factors engineer finds another indicator is necessary and space is an issue, a large redesign can be avoided by adding another indicator with a flexible ZLB routed from another LED that may be in a completely different location from the first LED. The coupling of design time and design space radically improve cost concerns in a variety of industries and applications. Five different colors of POF jackets improve installation and visual identification in the field by technicians, as well as clarify references in user manuals.
You make the call – guidelines on choosing the best type of light pipe
Rigid and flexible light pipes offer you two distinct options. Each one has advantages and disadvantages. Here are some guidelines to help you make the right choice.
Consider a rigid light pipe if these parameters apply to your project:
- Light only needs to travel a short distance
- Low cost is a top priority
- The printed circuit board is located close to the front panel with simple access available
Look towards using a flexible light pipe if:
- The light must travel a long distance
- The design of the equipment does not allow for a direct path from the LED to the display lens
- There is a possibility that additional indicators may need to be added later
- The human factors design is not yet finalized
- The LED output must travel through a high-EMI environment before reaching the lens cap.
Bivar engineers are always available to help you develop custom solutions to your most complex light pipe issues. Contact us!