Light Guide Plate Illumination for Capacitive Touch Buttons
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Solution Overview
Problem
Electronic devices face challenges in effectively illuminating buttons in low-light conditions without making them overly bulky or inadequately illuminated.
Innovation Solution
The use of a light guide plate with peripheral edges oriented at a non-zero angle, light-emitting diodes of different colors, and a light recycling retroreflector to create a backlighting system that illuminates capacitive touch sensor buttons through a transparent layer with symbol-shaped openings, ensuring efficient light extraction and distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional backlighting methods are used to illuminate buttons, then buttons can be viewed in low lighting conditions, but the device becomes overly bulky
Solution Approach 1:
The patent uses a thin light guide plate (LGP) with integrated optical features (ribs and bumps) to provide backlighting. The LGP is a thin film structure that guides light from LEDs at the edges and extracts it through controlled scattering, eliminating the need for bulky traditional backlighting components while maintaining effective button illumination.
Solution Approach 2:
The patent transitions from conventional face-mounted LED arrays to edge-mounted LEDs with light guidance through the LGP. This dimensional change allows light to be introduced from the edges and distributed across the button area, reducing the vertical profile and overall device volume while maintaining illumination effectiveness.
2Illumination intensity
If traditional backlighting methods are used to illuminate buttons, then buttons can be viewed in low lighting conditions, but the illumination is inadequate
Solution Approach 1:
The patent implements local quality control through strategically placed light extraction features. Ribs are positioned to collimate light in specific directions, while bumps create scattering centers at precise locations. This localized optimization ensures uniform light distribution across different button areas, providing reliable and adequate illumination where needed.
Solution Approach 2:
The patent controls illumination parameters by varying the geometry and distribution of ribs and bumps within the LGP. By adjusting rib angles, bump densities, and extraction region characteristics, the system optimizes light extraction efficiency and uniformity, ensuring reliable button illumination across different viewing conditions.
3Illumination intensity
If light is extracted from the light guide plate, then buttons are illuminated, but light is lost without being reused
Solution Approach 1:
The patent recovers light that would otherwise be lost by implementing a retroreflector at the bottom of the LGP. Light that passes through the button area without being extracted is reflected back into the LGP, giving it a second chance to be extracted and contribute to button illumination. This significantly reduces light energy loss and improves overall illumination efficiency.
Solution Approach 2:
The retroreflector enables continuous useful action by circulating light within the LGP. Instead of light being extracted in a single pass, the reflected light continues to propagate and can be extracted at subsequent opportunities, maintaining continuous illumination contribution from the same light source and reducing energy waste.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides clear and efficient illumination for buttons, enhancing user experience in low-light conditions while maintaining a compact design, by utilizing a light guide plate with angled edges and a retroreflector to recycle and focus light onto the button symbols.
Implementation Method 1
The light guide plate of the lighting system may have peripheral edges that are oriented at a non-zero angle with respect to each other
Implementation Method 2
The light may be extracted from the light guide plate using bumps in a light extraction region
Implementation Method 3
The light guide plate may have a light recycling retroreflector formed from a pair of angled peripheral edges. Light from the retroreflector may be reflected towards the light extraction region
Data Source
AI summary
An electronic device may have input-output devices such as buttons formed from capacitive touch sensor electrodes. A transparent layer may be provided with opaque masking structures having a symbol-shaped opening aligned with a capacitive touch sensor electrode for a button or other input device. The symbol-shaped opening may be adjacent to the electrode and may be illuminated with light from a lighting system. The lighting system may include a light guide plate. The light guide plate may have edges that are oriented at non-zero angle with respect to each other. Light-emitting diodes of different colors may emit light into the edges. The light may be extracted from the light guide plate using bumps in a light extraction region. Light may be collimated using ribs formed on an opposing side of the light guide plate.