Implementing Light Guide Film Backlighting

23 Mar, 2022

By hqt

Niceone-Keypad hopes this document will be of little help to clients, colleagues and anyone who wants to learn more about Light Guide Film Backlighting.

What is Light Guide Film (LGF)?

The material choices of Light Guide Film (LGF) are Polyester, Polycarbonate or Silicone diffusion film. A way to aggregate the LEDs light source through special ink dot printing or raised dot printing to enhance the LEDs light source so that the backlight area can be lit. Generally, the Light Guide film will be close to and at a certain distance from the LEDs. Even the same product will be placed with different Light Guide Films to achieve the best results. The specific design can be implemented by Niceone-Keypad’s engineering team. But there are also traces to follow. Below, please check some of the design limitations of Light Guide Film and how to make Light Guide Film achieve the best results.

Design limitations of Light Guide Film:

The Light Guide Film Membrane Switch has certain design constraints due to molds, Adhesive stickiness issues, and the brightness of LEDs, which is why this type of product is limited.

The first is Size:

There must be a certain distance between the button and the button, the logo and the logo and the bar. The main reason is that although there seems to be a distance of several mm between these buttons, the logo and the bar, the Adhesive and other raw materials behind them need to be reduced by about 0.5mm on one side. The knife mold and the stainless steel mold cannot flush out the adhesive tape 1 to 1 well, leaving more adhesive tape. Therefore, there must be a certain distance between the button and the button, the logo and the logo and the bar, otherwise there will be light bleed.

Next is the location of the LEDs:

The light-emitting area of ​​the side LEDs is 120°, and the best effect is achieved at a distance of 5mm from the button. However, if the product is limited, the distance between the button and the LEDs can be shortened, but additional LEDs are needed to increase the brightness.

Then there is the choice of LEDs:

The brightest LEDs are generally white, followed by green and red. But general customers need other color LEDs for backlighting such as orange, blue. Niceone-Keypad is not recommended for such weak LEDs. If this type of LEDs is still used, Niceone-Keypad recommends white clear ink to be combined with this type of LEDs. Or custom high-brightness LEDs but the cost will be relatively high. This is also an important reason for limiting the Backlight Membrane Switch, because some color LEDs do not have high brightness.

And finally the clear ink:

Since most users like Deadfront, Niceone-Keypad does not recommend black, red and other dark colors as Deadfront, because the ink will absorb part of the light emitted by LEDs, especially if the light is weaker LEDs. Unless you consider the combination of color printing and silk screen printing. For details, please contact Niceone-Keypad. Our engineering team will work with you on product design.

How to increase the brightness of Light Guide Film Membrane Switch?

  • Dimensions:

The distance between the LEDs and the area to be illuminated needs to be 5mm, because this is the time when the brightness of the LEDs is best displayed.

  • The design of the light guide plate:

Niceone-Keypad’s light guide plate mainly has two designs, printed light guide dots and light guide dots. By choosing the light guide plate designed by Niceone-Keypad, the brightness of the product can be effectively improved. This is because Niceone-Keypad uses a special material to upgrade the light guide plate. Contact Niceone-Keypad for a free Light Guide Film

  • Appropriately increase LEDs:

Adding light sources is beneficial for increasing brightness.

  • Use lower resistance wiring:

Use lower resistance circuits such as Flex Copper Circuit, Printing Circuit Board. This is because circuits with too high resistance such as Flex Silver Membrane Switch will make LEDs unable to fully perform their electrical properties, resulting in a significant reduction in the light source of LEDs. . However, the circuit resistance of the Flex Copper Circuit and Printing Circuit Board will be lower, which is conducive to the perfect electrical performance of the LEDs to achieve the function, and the light source will be brighter.

  • Use and selection of transparent ink:

Generally speaking, light colors such as white, purple and yellow have better light transmittance and are also the colors that Niceone-Keypad recommends customers to use. Such as dark colors black, red, etc. need to choose color printing and special LEDs to light it up.

  • Reasonable product design:

The perfect realization of the Light Guide Film Membrane Switch lies in the sound design, and fortunately Niceone-Keypad has a good group of engineers. Thanks to their efforts, Niceone-Keypad has implemented one Light Guide Film Membrane Switch after another.

The benefits of Light Guide Film Membrane Switch are:

1. The thickness of Light Guide Film Membrane Switch is generally less than 2mm, and the normal thickness is about 1.0mm. The Light Guide Film Membrane Switch is also a very light product due to its numerous features of the Membrane Switch. So suitable for small and light devices.

2. Compared with EL Membrane Switch, its power consumption is lower.

3. Can be used in a dark environment or a low-light environment.

4. Able to achieve different color light on the same panel. You can choose different color LEDs to illuminate different areas. Compared with optical fiber or EL sheet, the light source of individual color. Light Guide Film enables multiple light sources.

Things to consider for Light Guide Film Membrane Switch:

What is the size of the input voltage and input current, do I need to add resistance in the Membrane Switch?

Where is the use environment, a bright office or a ward in the dark or a low-light environment?

Does the product size allow manufacturers to implement Light Guide Film Membrane Switch?

Are there higher requirements for Tactile Feedback?

Does the product button need to be convex?

Is there a requirement for the thickness of the Membrane Switch?

You can contact Niceone-Keypad for specific case analysis

What is the distance limit in Light Guide Film Membrane Switch?

Distance Limits for Light Guide Film Membrane Switch:

A ≥5 Distance Between LED and ilumi
B ≥3 Distance between discrete illuminated areas perpendicular to light path.
C ≥3 Distance between discrete illuminated areas parallel to light path.
D ≥5 Distance between illuminated area and termination location.
E ≥0.3 Distance between edge of circuit layers and edge of overlay
F ≥3 Distance between light blocking spacer & part edge.

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