Backlighting Technologies and Solutions

Backlighting is a technology used for a variety of purposes in flat panel switches, with one of the most common being for backlighting of warning text or warning symbols. You’re likely to see backlighting used in industries such as aerospace and industrial applications. We offer three different backlighting options, creating endless lighting possibilities that can be fully integrated into Membrane Switches.

LED Diffuser options

There are several design options to diffuse the light on LEDs that are integrated into a Membrane Switch or as a LED layer mounted directly under a Graphic Overlay.

Clear gloss apertures can be designed into the Overlay Panel allowing for flexible design possibilies, with the absence of printing ink in these areas allowing for the brightest led illumination. However the LED may be visible through small apperture, which would be asthetically undesireable.

Semi transparent LED windows can provide reduced light diffusion and hide the LED from view, this effect is achieved by printing a diffuser as one of the colour layers during manufacture of the Graphic Overlay.

White or semi transluscent white diffused LED windows are the most common as this hides the LED from view and allows for a softer illumination of the Overlay. This effect is also acheived as a colour layer of the printing process.

Dead front LED windows and graphics can be acheived by printing transluscent or transparent colours behind the background colour, common colours are transparent grey and white. By printing other colours behind translucent white, colour changes can be acheived when the LED is illuminate, an example would be a white deadfront that changes to green, red, blue etc.

To minimise the thickness of the Membrane Keypad when LEDs are included, it is common practice to emboss the LED windows, this also gives a wider viewing angle of the LED.

LED Backlighting

To break it down, LED backlighting is when we mount SMD LEDs and other components to the LED Circuit layer. Then on the layer above we add a piece film (called light guide film), this film directs the light to the areas that need to be illuminated. Our design engineers will advise you on the appropriate backlighting options for your project. Once we know what you’re looking for and what you would like to achieve, we can guide you to the suitable options to ensure you make the best decision.

EL Backlighting

An EL lamp is a Light Emitting Capacitor (LEC). As with any capacitor the LEC is made of a dielectric material sandwiched between two parallel conductors. It differs from a normal capacitor because the dielectric is a phosphor that will emit light when energised with an alternating electric field and the top conductor is transparent which allows the illuminating phosphor to be visible.

EL lamps are thin, flat, with flexible cold illumination sources that can be printed with complex shapes and be easily integrated into products where space and/or power are limited. They are commonly used where back lighting is required, for example in LCD displays, aircraft and marine instrument panels, agricultural devices and industrial user interface devices.

The flexibility of an EL lamp allows curved surfaces to be illuminated and they can withstand stress when used over a membrane switch. The transparent conductor in an EL lamp is usually a polyester film with a conductive coating. At Reid Industrial Graphic Products we screen print conductive inks only in the areas that are required to be lit. The polyester films used in the construction of EL lamps can either be heat stabilised or hard coated films, the choice is determined by the actual application.

MacDermid Autotype offer a range of heat stabilised and hard coated polyester films that have excellent receptivity to screen printing with conductive inks. For further details on these products see the product information section on Autostat for heat stabilised films and Autoflex and Autotex for hard coated films.

What’s great about Lumitex, is that it can provide light to sensitive applications. Lumitex is fibre optic and usually only powered by a single LED, which means that you won’t experience any problems with heat. This is because fibre optic doesn’t generate heat, it simply carries the light source. Benefits of Lumitex include, but are not limited to, thin design, simplicity to implement and long life (100k+ hours in most configurations).

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