LED Wavelength Shift Compensation via Dual Electrical Biasing

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Solution Overview

Problem

Existing methods for controlling the intensity of light emissions from LEDs, such as PWM and CCR, result in unacceptable wavelength shifting and color distortions, especially at low intensities and varying temperatures, which are not effectively addressed by current solutions.

Innovation Solution

A method and apparatus that utilize a combination of electrical biasing techniques, such as superposition or alternation of PWM and CCR, to maintain a stable emitted spectrum by compensating for wavelength shifts, ensuring minimal color change across intensity levels and temperature variations without requiring extensive feedback systems.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If PWM or CCR methods are used to control LED intensity, then light intensity can be adjusted, but wavelength shifting and color distortion occur especially at low intensities and varying temperatures

Engineering Contradiction:

Improvelight intensityVSAvoidemitted spectrum stability

Core Design Contradiction:

Illumination intensityVSStability of the object's composition

Solution Approach 1:

The patent applies parameter changes by adjusting the forward current through the LED in a controlled manner to compensate for wavelength shifts. The system dynamically modifies current parameters (magnitude, pulse width) to maintain stable perceived color across varying intensity levels and temperatures, directly addressing the spectral instability problem

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback mechanisms by monitoring the emitted spectrum and adjusting the forward current accordingly. The system uses the observed wavelength shifts as feedback to modulate the current waveform, creating a closed-loop control system that maintains spectral stability despite intensity variations

Inventive Principle:

Principle #23Feedback

2Productivity

If forward current is varied to regulate LED intensity, then light output can be controlled, but wavelength shifting occurs due to temperature and current effects

Engineering Contradiction:

Improvelight output controlVSAvoidwavelength control precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent employs periodic action through pulse width modulation (PWM) of the forward current. By applying periodic current pulses with varying duty cycles, the system achieves precise intensity control while the periodic nature helps stabilize the LED junction temperature, thereby reducing wavelength shifts caused by thermal effects

Inventive Principle:

Principle #19Periodic action

3Illumination intensity

If linear regulator is used to regulate LED current, then intensity control is achieved, but power losses increase and complexity increases

Engineering Contradiction:

ImproveLED current regulationVSAvoidpower loss

Core Design Contradiction:

Illumination intensityVSLoss of energy

Solution Approach 1:

The patent replaces the linear regulator (analog/mechanical control system) with a pulse width modulation-based switching control system. This substitution eliminates the continuous power dissipation inherent in linear regulators by using high-frequency switching, thereby significantly reducing power losses while maintaining precise current regulation capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses periodic switching action in the current regulation circuitry, where the LED current is controlled through periodic pulses rather than continuous analog regulation. This periodic control method reduces energy dissipation by minimizing the time the regulator operates in its dissipative region, thereby reducing overall power losses

Inventive Principle:

Principle #19Periodic action

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

The solution provides stable color emission and reduced power losses, increasing efficiency and reducing the complexity and cost of control systems, while maintaining the perceived color constant across a range of intensities and temperatures.

Implementation Method 1

a light-emitting diode is a semiconductor device that emits incoherent, narrow-spectrum light when electrically biased in the forward direction of its (p-n) junction

Methodology Applied

Scientific EffectLight emission from LED: Light Emitting Diode

Implementation Method 2

emits incoherent, narrow-spectrum light when electrically biased

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS8704456B2Regulation of wavelength shift and perceived color of solid state lighting with intensity variation

Publication Date: 2014.04.22 E2E SYSTEMS LLC

AI summary

Representative embodiments of the invention provide a system, apparatus, and method of controlling an intensity and spectrum of light emitted from a solid state lighting system. The solid state lighting system has a first emitted spectrum at a full intensity level and at a selected temperature, with a first electrical biasing for the solid state lighting system producing a first wavelength shift, and a second electrical biasing for the solid state lighting system producing a second, opposing wavelength shift. Representative embodiments provide for receiving information designating a selected intensity level or a selected temperature; and providing a combined first electrical biasing and second electrical biasing to the solid state lighting system to generate emitted light having the selected intensity level and having a second emitted spectrum within a predetermined variance of the first emitted spectrum over a predetermined range of temperatures.