LED Drive Current Computation for Signboard Color Accuracy
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Solution Overview
Problem
LED-based signboards face challenges in maintaining color accuracy and reliability due to ambient light changes, limited color gamut utilization, and frequent LED failures, which affect the aesthetic impact and maintenance costs.
Innovation Solution
A method computes drive currents for LEDs to achieve desired colors and luminous intensity using linear programming, dynamically circumvents faults by altering intensities of functional LEDs, and expands the color gamut by adjusting current through each LED kind, while minimizing the impact of ambient light through photometric equations and sensor measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the intensity of light emitted from each LED kind is controlled by electrical current to produce a wide variety of colors and intensities, then color gamut and luminous intensity control are improved, but the system becomes sensitive to LED failures and ambient light changes affecting reliability
Solution Approach 1:
The patent changes the parameters of drive currents dynamically to compensate for LED failures and ambient light changes. By adjusting the intensity parameters of remaining functional LEDs and recalculating drive currents using photometric equations, the system maintains desired color and luminous intensity despite component failures or environmental changes.
Solution Approach 2:
The system implements feedback by detecting LED failures and ambient light conditions, then using this information to recalculate and adjust drive currents. The control system continuously monitors the state of LEDs and modifies operating parameters to maintain display quality and color accuracy under varying conditions.
2Use of energy by moving object
If pulse-modulated current sources are used to control LED intensity with duty cycle modulation, then energy efficiency and control precision are improved, but the system complexity increases due to additional control circuitry and timing requirements
Solution Approach 1:
The patent employs periodic pulse-modulated current sources that switch between on and off states at high frequency. By using duty cycle modulation where the average current is controlled through the ratio of on-time to total period, the system achieves efficient LED control with reduced energy consumption while maintaining precise intensity control.
3Manufacturing precision
If linear programming is used to compute optimal drive currents for multiple LEDs subject to constraints, then color accuracy and luminous intensity precision are improved, but computational complexity and processing time increase
Solution Approach 1:
The patent formulates the drive current calculation as a linear programming problem where the objective is to maximize luminous intensity while satisfying color accuracy constraints and LED individual maximum intensity constraints. By expressing the photometric equations in linear form and using standard linear programming algorithms, the system achieves precise color and intensity control through optimized parameter selection.
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 approach maintains color accuracy and reliability by compensating for ambient light, effectively utilizing the full color gamut, and reduces downtime and maintenance costs by dynamically handling LED failures and optimizing LED usage.
Implementation Method 1
Light emitting diodes (LEDs) produce most of the active images shown on modern advertising structures
Implementation Method 2
Each 'kind' of LEDs may consist of a single LED, or a serially connected string of LEDs, providing a specific color of light
Data Source
AI summary
A method computes drive currents for LEDs in a pixel of a signboard to achieve a desired color at a desired luminous intensity. This method is particular applicable to a signboard having pixels made up of four (4) or more primary colors. The method selects a number of colors within a color gamut, and for each selected color, the method computes drive currents for the LEDs of each basis color, such that the resulting luminous intensity of the selected color is maximum. Using the computed drive currents, the method then scales the drive currents to achieve the desired luminous intensity in the desired color. The drive currents may be computed, for example, using a constrained maximization technique, such as linear programming. In one embodiment, the drive currents for each selected color are computed subject to the constraint that none of the drive currents is negative, and that their total is less than a predetermined value. In one embodiment, the selected color is expressed in the units of a linear color space.