LED light guide for product and panel building
3.5 minutes | 22 Nov 2019
Some type of light source is fundamental in many products designed for both consumer and commercial use. In years past, incandescent lamps were the source of most lighting requirements.
While obviously used for lighting the environment, these lamps were also a staple component for indicator lights in various types of electrical and electronic equipment. However, for approximately the past three decades, a new light source has been and continues to be developed: the light emitting diode or LED.
LEDs are a type of semiconductor light source that combine a P-type semiconductor with an N-type semiconductor. Applying the proper voltage – a low voltage DC current in most cases – the electrical energy is converted directly into light. The process is more efficient and wastes less energy than conventional incandescent or fluorescent lamps.
For instance, an incandescent bulb provides between 750 – 2000 hours of light. Compare that to halogen, which lasts between 2,000 – 4,000 hours. Now compare both to LED lighting: 35,000 – 50,000 hours. But not only is LED lighting durable, it’s also energy efficient, which answers the demand for less energy consumption.
LEDs are available in three basic colours: red, green, and blue. Two configurations are available: a lamp type, which resembles a small glass bulb with two leads, and the chip type that mounts to the surface of printed circuit board, or PCB as it’s commonly known as. The type used depends on the application.
Presently, there is no "white" LED. The white light is accomplished by either combining the three primary colours to mimic white, or by using a blue LED with a yellow phosphorus coating. Look into the lens of an LED flashlight and you'll see the yellow coating.
When used as indicator lights, the chip type is commonly used. The PCB is mounted in close proximity to the panel surface, less than two inches away. To route the light to the panel surface lens, an LED light pipe is attached to the circuit board, directly over the chip. The source light is reflected through the pipe (a plastic or acrylic bar or tube) and emitted from the indicator lens.
Light pipe technology is an exacting science. The proper LED light pipe design is done by LED lighting specialists using complex software and techniques.
When used in PCBs, the boards are spaced to avoid heat damage. This is accomplished by using PCB spacers or mounts. One such mount, a locating PCB support spacer, is designed with an arrowhead snap-lock to mount it to the bottom board, and has a long nose snap fit end that easily guides the top board into position.
The information used to activate the LED indicator light is often directed from one PCB stack (multi-board assemblies) to the board or stack where the LEDs are installed. This is usually accomplished through ribbon cables, linking the boards. These cables are routed from one stack to the other inside the enclosure.
To keep the cable installation clean and manageable when the PCBs are not mounted directly to each other, a flat cable clamp is used, often with an adhesive backing for easy installation. This arrangement will allow the computer or other information source to be mounted on the enclosure backplate, and the LED board to be attached to the panel or enclosure door.
Lamp-type LED considerations
Lamp-type LEDs can be mounted directly to the PCB if external cabinet indication is not needed. While it can be soldered directly to the board, an LED light mount is often used to space the lamp from the PCB. LED spacer mounts are used when an array of LEDs is installed on the board, such as in a row or column. An LED spacer not only gives a clean appearance but can protect the LED leads from damage.
If it's desirable for the LED to be mounted parallel to the board surface, a 90° LED light mount is used.
Some applications require surface mounted led panel light installations. An LED light pipe panel mount places the indicator on the surface of the panel, not light directed through an LED light pipe. A through hole LED is held in place using an LED lens holder. (Note: with surface mount LED light fixtures, or any LED lighting, it’s important to know the through hole LED polarity. Always look over your product data sheets, which will tell you.)
One type of LED light mount snaps into the hole in the panel, and the LED clicks into place from the reverse side or rear of the panel.
For LEDs located further from the PCB, or even in an adjoining cabinet, fibre optic light pipes are used. A bundle of fibres is encased in a sheath to keep them together and help reflect the light through the pipe. Because they must be routed around components in the cabinet, cable mounting clips are used to prevent damage to the delicate fibre optics. They're somewhat brittle, so careful attention must be paid to any cable bend radius. In other words, make sure you do not exceed the acceptable bend radius or you could damage the fibre.
In closing, LEDs are valuable additions to panel board design. They're easy to install, have a longevity that far exceeds that of incandescent lamps, and require less power or voltage than other lamps.
Summary: You might need:
|Flat Cable Clamp|
|Arrowhead Snap Lock|
|Round Imperial Extruded Spacer|
|Round Imperial Extruded Spacer|
|90° LED Mount|
|Clip and Ring LED Mount|
|LED Lens Holder|
|LED light pipe|
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