March 12, 2020 by Emmanuel Ikimi
LEDs (or light-emitting diodes) are the most commonly used indicators in electronics.
However, LEDs are hardly used by themselves: they are often combined with LED light pipes: unique structures that increase visual feedback on user interfaces. In this article, we define light pipes as a tool and discuss their applications and benefits to engineers.
LED light pipes (aka light guides) are transparent coverings or structures with excellent luminous transmittance used to transport emitted light from surface-mount or through-hole LEDs to a user interface (e.g. an ‘ON/OFF’ indicator)
LED light pipes are cost-effective, efficient, and flexible solutions utilised for visual indication in a host of electronic equipment and devices.
There are two main types of LED light pipes: rigid and flexible. Rigid light pipes are made of glass or polycarbonate materials and mounted directly on the LED.
Due to the former’s rigid design, they have a vertical or right-angle orientation, making them unsuitable for transporting light across sharp bends. Flexible light pipes, on the other hand, are made of optical-grade fibres. They attach to an LED adapter mounted on the PCB and can transfer light across sharp bends and steep angles.
An example of an LED light pipe. Image Credit: Radiant Lighting.
Electrical engineers should consider the following to help them select the best LED light pipes for their designs.
Placement is one of the most essential considerations for choosing a light pipe is knowing how it will be placed. Additionally, engineers should know the maximum distance between the light pipe and the LED. Rigid—i.e. vertical or 90-degree-angle—light pipes are suitable for LEDs that are mounted on a PCB directly behind a panel. Alternatively, flexible light pipes are ideal for LEDs mounted at a wide-angle from the front of the panel (or relatively further away).
Another factor to note is the amount of light emitted by the light pipe. The luminous emittance depends on the type of material that the light pipe is made of, as well as the shape of its lens (the front part of the pipe). Light pipes should capture at least 80% of the light emitted from the source.
Light loss (aka backlight bleed), a fairly common issue when using light pipes, involves light escaping from within the covering/structure and glows around the edges, causing uneven illumination. To avoid backlight bleed, the shape and size of the light pipe must accurately match that of the LED.
LED light pipes provide the following benefits to electrical engineers:
They provide uniform illumination: LED light pipes can transport up to 80% of the light emitted from an LED source—up to several inches with low light loss, shadowing, and glare.
They increase design flexibility in visual applications: light pipes come in a wide range of shapes, colours, sizes, and configurations. This allows greater design flexibility: for example, Bivar LPAR and LPAV light pipe arrays comprise multiple pipes for transmitting light to several indicators on one control panel.
They reduce design costs: light pipes are a cost-effective way for engineers to integrate visual indicators into electronic devices and equipment. Engineers using light pipes in their designs can save up to 50% of the costs of using fibre-optic technology.
They minimise electrostatic discharge: using light pipes can help to prevent electrostatic discharge in electronic equipment. This is by isolating the LED from other PCB components.
They reduce the time-to-market: due to the ease of installation, LED light pipes allow manufacturers to speed up production and go to market faster. Using computer-aided design/modelling software, engineers can design custom solutions to suit a host of applications.
A computer-generated image of an LED light pipe array. Image Credit: Lumex.
Due to their efficiency, flexibility, and cost-effectiveness, LED light pipes can be utilised for visual indication in a multitude of industrial, consumer, medical, and communications applications.
Let’s take a closer look at these applications below.
Control panels for industrial process control use LEDs to communicate the status of machinery to workers at the plant (e.g. ‘ON/OFF’, ‘normal operation’, ‘fault condition’, etc). Using light pipes as visual indicators enhances the illumination from the given LEDs, so they are seen more clearly.
Visual indicators are vital components of security/surveillance systems, particularly for residential, industrial, and commercial facilities. LED light pipes help to increase visual communications on the control panels to alert homeowners or security personnel in the event of security breaches. They come in a wide range of sizes and orientations to suit any application.
Consumer devices, such as computers, printers, handheld cameras, and white goods utilise LED light pipes on user interfaces. Rigid and flexible light pipes are used to bend light across corners.
Light pipes can transfer light from surface-mount or through-hole LEDs to the user interfaces of communication systems (consider network switches, routers, emergency-assistance call boxes, and so on).
All in all, light pipes are simple-to-use and cost-effective solutions for electronic devices and equipment that require visual indication on a user interface. LED light pipes are available in a broad range of materials, shapes, colours, and orientations to suit any type of design.
Engineers can benefit from incorporating LED light pipes into their designs—to ensure lossless light transfer from the PCB to the user interface.
