How to backlight a membrane or touch switch
Backlighting switches for improved user interfacesWhile not always a design requirement, many switches feature a backlight. This component works to illuminate the front of the switch so that it’s easier for users to see. But, while most people are familiar with the general concept of backlighting, few know the specifics of how it works.
Backlighting for membrane and touch switches works in a similar way as backlighting used in other devices, including liquid-crystal displays (LCDs). Within the switch is a backlighting component that’s designed specifically for the purpose of illuminating the front of the switch. The switch backlighting component activates when the device is turned on, illuminating the upper layer of the switch.
There are several different backlighting solutions for switch manufacturing. Below we’ll explore the various types of backlighting options and factors that make each type more suitable for various applications.
Light-emitting diodes (LEDs)
What is LED Backlighting?
As the name suggests, LED backlighting involves the use of light-emitting diodes, or LEDs. Unlike traditional bulbs, such as incandescent, LEDs don’t have a filament; instead, they use a semiconductor to create light. When electricity flows through the semiconductor, it releases a narrow and concentrated stream of light particles, resulting in a bright light.
When backlighting a switch, LED bulbs are embedded or mounted inside, generally (but not always) on the surface of the circuit layer. When the LEDs are illuminated, light flows through the top layer of the switch.
Pros and cons of LED backlighting
LED has become a preferred backlighting technology in recent years because of its energy-efficient properties. In today’s world of portable devices, this is especially beneficial because it enables less frequent recharging or replacement of the battery. Some additional benefits of LED backlighting are its:
- Long lifespan (50,000+ hours of continuous use and over 100,000 hours in some applications)
- Low heat production
- Wide range of colors
- Low-profile design capabilities
Although effective and easy to implement, LEDs have a tendency to create bright spots, restricting their utility as a full-panel backlight for membrane switches. Nelson Miller Group has industry-leading expertise in the development of Light Guide Films (LGF) to support the even distribution of LED backlighting.
Electroluminescent (EL)
What is an EL backlight?
Electroluminescent (EL) backlighting uses phosphor compounds to generate light using electroluminescence—the illumination of the phosphor compounds when exposed to electricity. With an EL backlight panel, a layer of phosphor is printed between two conductive layers. When the device is turned on, electricity will flow through the two conductive layers as well as the phosphor layer in the middle. The phosphor compounds illuminate when exposed to the electrical current, illuminating the switch above.
The color of an EL backlight will ultimately depend on the color of the phosphor it uses, since different compounds create different colors. As a result, manufacturers can create switches with a specific color of backlighting by using the right type of phosphor compounds in the EL bulbs.
Pros and cons of EL backlighting
Like LED backlighting, EL is available in small sizes and multiple colors, and is very energy- and cost-efficient. Unlike LED, though, it provides uniform lighting without dark or bright spots.
The biggest downside to EL backlighting is its comparatively short lifespan compared to LEDs. The average EL panel lasts approximately 8,000-10,000 hours, vs. 50,000+ hours for LEDs. What’s more, EL panels often experience a decrease in brightness and uniformity over time as they age. As its phosphor compounds begin to decay, EL backlighting may fail to generate a sufficient amount of light.
Fiber optic
What is fiber optic backlighting?
Unlike LED and UL backlighting, fiber optic backlighting doesn’t generate its own light; rather it consists of many small strands of optical fiber, generally made of glass but sometimes of plastic, that distribute light throughout a switch to illuminate it. Optical fiber backlighting is most often used in conjunction with LEDs.
Generally, a rectangular or square-shaped source of illumination is created using two or more layers of woven fiber optic cable. On one end, the fibers are grouped together to form a circular ferrule. It’s then connected to at least one lighting source (generally LEDs). The light is reflected within the fiber optic cables, creating an efficient and high-speed transmission of light throughout the switch.
Pros and cons of fiber optic backlighting
Because it is generally powered by LEDs, fiber optic backlighting features a long lifespan up to 100,000 hours. Fiber optic protects against bright and dark spots by evenly distributing light across the device, and it reduces the number of LEDs needed (therefore improving energy efficiency). Because optical fibers are resistant to moisture and extreme temperatures, it’s a functional backlighting option for switches in high-humid or otherwise extreme environments.
Fiber optics aren’t without their downsides, however. Installation tends to be very complex and labor-intensive compared to other backlighting solutions, such as LED. Combine this with the high cost of the optical fibers themselves, and fiber optic backlighting tends to be quite expensive. Optical fibers can additionally be sensitive to bending or stress, which can lead to breakage or reduced light transmission. Other factors such as light loss, color changing, and the ongoing maintenance needed further limit the number and type of applications in which fiber optic backlighting is appropriate.
Choosing the Right Backlighting Solution
As outlined above, you’ll find many of the same benefits when considering EL and LED backlighting. They are both cost- and energy-efficient, available in low-profile designs, and support multiple colors. In addition, LEDs coupled with effective light guides boast similar uniformity to EL.
EL can be appropriate in specific applications where temporary or intermittent lighting is required, and/or if a specific (often vintage) aesthetic is desired.
Fiber optic backlighting can be valuable in applications where point-to-point light transmission (particularly over long distances), minimal heat emission, and electrical isolation are necessary.
LED is the leading choice for switch backlighting in most applications because of its long lifespan, ability to maintain its brightness with minimal deterioration, small size, broad color options, and low heat production. As LED technology continues to advance, customers will benefit from even more improvements in performance, color quality, and cost.
When you partner with NMG, you benefit from our team’s many decades of backlighting experience, dating back to the 1930s. We can help identify and design the right backlighting solution for your project, as well as support with your device’s manufacturing and supply chain management. Contact us today to get started!
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NMG has more than 85 years of experience partnering with organizations to bring their industrial, IoT, lighting, medical, telecommunications, consumer, and aerospace products to life. We solve your most complex challenges in engineering design, manufacturing, and supply chain management.
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