Hybrid Fluorescent LED Backlight for Flat Panel Displays
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Solution Overview
Problem
Existing methods for illuminating flat panel displays, such as those in aircraft cockpits, struggle to provide continuously-variable illumination levels from very low to very high without reducing the lifespan of fluorescent tubes due to repeated rapid restarts for pulse width modulation.
Innovation Solution
Incorporating a combination of fluorescent tubes and light-emitting diodes (LEDs) with a control circuit that dynamically adjusts illumination based on ambient light conditions, allowing for smooth brightness variation over a wide range without excessive wear on the tubes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation is used to reduce illumination to extremely low levels, then the desired low brightness is achieved, but the fluorescent tube lifespan is significantly reduced due to repeated plasma ignition
Solution Approach 1:
The illumination control is segmented into two distinct ranges: a first range (approximately 1-100 foot-lamberts) controlled by continuous dimming of the fluorescent tube, and a second range (approximately 0.001-0.1 foot-lamberts) controlled by switching between fluorescent and LED backlighting. This segmentation allows each lighting source to operate in its optimal control mode, avoiding the harmful effects of PWM on the fluorescent tube.
Solution Approach 2:
A photosensor acts as an intermediary device that detects the actual backlight output and provides feedback to the controller. This feedback mechanism enables the system to automatically adjust the illumination level within the first range by modulating the fluorescent tube's power supply, thereby achieving smooth dimming without PWM and extending tube lifespan.
2Ease of operation
If continuous current reduction is used to dim the fluorescent tube, then smooth brightness control is achieved, but the plasma cannot be maintained below a certain brightness level
Solution Approach 1:
The system changes the operating parameters of the backlighting by switching between two different light sources (fluorescent and LED) with different operational characteristics. The fluorescent tube handles the first brightness range with smooth continuous control, while the LED handles the second range, thereby achieving both smooth control and extremely low brightness levels that would be impossible with the fluorescent tube alone.
3Device complexity
If a single fluorescent tube is used for backlighting, then the system is simple, but it cannot provide both high and extremely low illumination levels without damage
Solution Approach 1:
The system merges two different backlighting technologies (fluorescent tube and LED array) into a single integrated system. The controller intelligently switches between the two sources based on the required brightness level, combining their respective advantages: the fluorescent tube's ability to provide smooth dimming in the higher range and the LED's ability to provide extremely low brightness levels without the drawbacks of PWM on fluorescent tubes.
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
Enables the FPD to maintain a broad range of illumination levels from 10,000:1 without significantly reducing the fluorescent tube's lifespan, ensuring pilots can view data under varying conditions without rapid wear and providing a backup in case of tube failure.
Implementation Method 1
an electric current flowing through the tube ionizes a vapor confined within the tube to create a plasma or ion cloud which, in turn, causes a phosphor coating on the interior surface of the tube to fluoresce and thereby emit visible light
Implementation Method 2
an electric current flowing through the tube ionizes a vapor confined within the tube to create a plasma or ion cloud
Implementation Method 3
a plurality of light emitting diodes (LEDs) positioned at or proximate the rear face or peripheral edges of the display and connected to a control circuit
Data Source
AI summary
A backlit flat panel display includes a fluorescent tube positioned for illuminating the display, and a plurality of display illuminating LEDs on the periphery of the display. The fluorescent tube illuminates the display through a first range of brightness above a predetermined transition level and the LEDs illuminate the display through a second range of brightness below the transition level. When the illumination of the display is adjusted through the transition level to account for changes in ambient light, the LEDs and the fluorescent tube are operated together, so that the combined brightness of the illumination provided by the LEDs and the fluorescent tube will provide the desired display brightness; this advantageously compensates for delayed illumination of the fluorescent tube at start up and for persistence in the tube after shutdown.