Considerations for Pairing Light Pipes with LEDs

There are two main components in a light pipe design: the LED light source and the light pipe. The design engineer must pay close attention to the pairing of the light pipe and the LED to minimize light loss and ensure best performance.

The LED must be effectively matched to the entrance of the light pipe to allow for proper light capture for maximum light transfer.

The importance of reducing light bleed

Light bleed occurs when light from the LED can be visible around the LED and light pipe area. Light bleed causes false-readings, muted and blended colors, crosstalk between adjacent light pipes, and unwanted glow in the enclosure.

When a rigid light pipe is located over the LED, it allows for a certain amount of light bleed at the base of the light pipe. A flexible light pipe is designed to provide less light bleed with a coated optical fiber and a light resistant black adapter. Rigid and flexible light pipes can also be PCB mounted. To eliminate light bleed, rigid and flexible light pipes are now available with a fully enclosed adapter as well.

Maximum design flexibility occurs when the designer can choose between designing with individual components (LED and light pipe) or using a complete system solution that includes both elements. Bivar offers both options.

LED Choices for light pipe pairing

Two types of LEDs are commonly available. Surface mount LEDs, often called SMD (surface mount device) LEDs, are mounted on the surface of the PCB and are smaller and brighter than through hole LEDs. Both types are offered in a wide range of sizes, colors, luminosities, and powers. Through-hole LEDs are mounted by inserting leads through the PCB and soldering to provide a stronger connection between layers; the soldering also increases protection against mechanical stress.

LED Specifications

Some key LED specifications are:

• Size: Through-hole LEDs are sized in millimeters (1.8mm, 3mm, 5mm) and SMD LEDs are based on industry standard package sizes. For example, an 0402 package (SM0402) has dimensions (length × width) of approximately 0.4mm X 0.2mm.
• Color: Both types of LEDs are available in a wide range of single colors. SMD LEDs have additional options, including white or single, bi-color and tri-color, in an array of color configurations.
• Brightness: LED light output (brightness intensity) is commonly measured in millicandelas (mcd) or lumens (lm). The higher the mcd or lm rating, the brighter the light intensity.

LED choices from Bivar

Bivar offers industry-standard SMD LEDs for individual use or with Bivar rigid or flexible light pipes. A wide variety of colors and luminosities are available, depending on package. LEDs in reinforced packages are suitable for use in harsh environment conditions. The table below shows some suitable Bivar SMD LEDs sorted by size. Each model has numerous colors available.

Through-hole LEDs are also available.

Standalone light pipes

It is important to pair the LED with an appropriate adapter to best suited for your application. Decision factors include space constraints, power requirements, desired brightness, and PCB mounting requirements.

Bivar offers adapters that are designed for use with already installed LEDs, plus integrated solutions with a built-in SMD or through-hole LED. Figure 1 shows the SMFLP adapter designed for an existing SMD LED that must be paired with an optical fiber/lens cap to form a complete flexible light pipe system.

Figure 1: The SMFLP adapter pairs a flexible light pipe with a pre-existing SMD LED

ZeroLightBleed™ technology eliminates light bleed

In addition to the adapters discussed above, Bivar’s innovative ZeroLightBleed™ (ZLB) technology eliminates light bleed in both rigid and flexible light pipes. The ZLB adapter channels light directly to the lens.

Figure 2: ZeroLightBleed™ adapter with built-in surface mount LED

Figure 2 shows the component parts. The adapter assembly is soldered directly to the PCB, thus strengthening the attachment to the PCB. The new light pipe system is optimal for high vibration applications. The new system makes sourcing simple by including the ZeroLightBleed™ adapter, LED, and light pipe in one, delivering convenience and resource savings for both procurement and assembly. The adapter offers built-in single, bi-color, and tri-color LEDs in a choice of fourteen colors.

ZeroLightBleed™ solutions for flexible light pipes

The SZ family combines the ZLB adapter with a Bivar SMD LED and a flexible light pipe. Three mounting options are available: Surface Mount, Firm Retention and Post Retention. The optical fiber offers a choice of 1mm or 2mm, a choice of six colors, and lengths from 1 in to 100 ft.

Figure 3 (a) SZ ZLB system (b) mounting options

ZeroLightBleed™ solutions for rigid light pipes

Bivar offers a ZLB solution for rigid light pipes in the LPR and LPV product families. These products are available in right angle (LPR) and vertical (LPV) configurations. The all-in-one adapter system is built with optimum light pipe and LED compatibility, making light pipe design easy and delivering con­venience and resource savings for procurement and assembly. Figure 4 shows an LPR example.

Figure 4: LPR Zero Light Bleed Adapter with a right-angle light pipe

The LPR and LPV combine the most compatible LED and rigid light pipe pairings and provide maximum light transmission while eliminating light cross talk between light pipes.

Light pipe systems with integrated LEDs

Integrated options are also available. The ORFLP system (Figure 5), for example, is a board-mounted adapter system with a built-in Bivar 4-pin Through-Hole Superflux LED and flexible light pipe for vertical applications.

Figure 5 (a) ORFLP system with through-hole LED (b) placement of LED in adapter

The FLPR2-XX adapter (Figure 6) offers a built-in through-hole LED with a right-angle mounting.

Figure 6 (a) FLPR2-XX system with through-hole LED (b) placement of LED in adapter

The designer can choose from hundreds of combinations of LED color and light pipe length.

Conclusion: something for everyone!

When pairing a light pipe and an LED, it’s important to maximize light transfer and minimize light bleed.

In cases where there is an existing through-hole or SMD LED, an appropriate light pipe and adapter are required, and Bivar offers options for both rigid and flexible light pipe installations. A new design can achieve the best performance with Bivar’s ZeroLightBleed™ adapter that combines a Bivar SMD LED with either a flexible or rigid light pipe.

Either way, there’s something for all application needs. Contact us to get started!