With so many options on the market, choosing the correct backlighting solution for your HMIs may seem like a daunting task. HMI backlit overlays come in 3 categories: electroluminescent lighting (EL), fibre optic lighting, and light guide films (LGFs), which also contain light-emitting diodes (LEDs). In this article, we’ll discuss their respective characteristics, allowing you to make the most appropriate choice.

HMI type

Backlight compatibility mainly depends on the type of your HMI. For instance, only LGFs and fiber optic lights can be used to illuminate capacitive keyboards, while all three options are a good match when producing custom membrane switches.


When considering backlit overlays, it’s best to evaluate the conditions in which your HMI will be used, as they will largely influence your decision.

EL: Used to illuminate large surface, EL requires minimal energy while diffusing a uniform light, which is perfect for lowlight or nighttime applications.

Fiber optic: Fiber optic lights have a longer service life than EL and are therefore well suited to demanding environments, such as outside applications. Although visible during the day, this technology is recommended for lowlight or nighttime usage. Depending on your needs, fiber optic lights may also be suitable when uniform lighting is required.

LGF and LED: Consisting of a thin diffuser film placed between two LEDs, LGFs are also recommended in harsh environments, as they’re capable of withstanding a wide range of temperatures, from extremely cold to exceedingly hot. Contrary to EL and fiber optic lights, which require a separate power supply, LGFs are connected directly to the circuit cable.
Moreover, LGFs and LEDs allow for a uniform distribution of light.

Power supply

Both LEDs and fibre optic lights use direct current (DC), which is unidirectional. It’s important to note that the majority of HMIs use this type of power source.

In order to emit light, EL requires alternative current, which is found in standard electrical sockets. For this reason, it relies on an AC power supply or an inverter in order to function.

Aesthetic needs

EL and fiber optic lights are generally used to backlight an HMI’s entire surface. Unlike LGFs, they therefore cannot be used to illuminate many small independent areas.

LGFs and fiber optic lights also come in a wider variety of colours, which may be a sizable asset depending on the intended product.

Memtronik offers a large selection of backlighting solutions, all designed to fit your specific needs. We can also assist you with product engineering, allowing you to meet user expectations and stay on top of the competition. Contact us to get a quote!