LED Brightness Control Using Reference LED Copying

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Solution Overview

Problem

LED lamps experience brightness degradation over time, leading to inconsistent illumination, and existing solutions with photo-detector based optical feedback circuitry are costly and complex.

Innovation Solution

Incorporating an additional LED as a reference light source, which is used infrequently and at lower current density, to maintain constant brightness, with embodiments using either a separate light detector or utilizing illumination LEDs for detection, thereby simplifying and reducing the cost of optical feedback control circuitry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If photo-detector based optical feedback circuitry is used to maintain fixed brightness, then brightness stability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvebrightness stabilityVSAvoidcircuitry complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent uses a copy of the illumination LED (a reference LED with identical characteristics) to create a stable reference signal. This reference LED is driven at a fixed current and serves as a template for comparison, allowing the system to detect brightness degradation without requiring complex photo-detector based optical feedback circuitry

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces the mechanical/optical photo-detector based feedback system with an electrical comparison method. By using a reference LED and comparing drive currents electrically, the system eliminates the need for physical optical detectors and complex feedback circuitry, reducing device complexity while maintaining brightness stability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If photo-detector based optical feedback circuitry is used to maintain fixed brightness, then brightness stability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvebrightness stabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The reference LED serves as a simplified copy that can be manufactured using the same process as the illumination LEDs. This approachable manufacturing method reduces costs compared to incorporating expensive photo-detectors and complex feedback circuitry into each lamp

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The reference LED is designed to be a simple, low-cost component that can be easily replaced if needed. Its straightforward design and manufacturing process make it much cheaper than photo-detector based systems, even though it may have a limited operational lifespan compared to the main illumination LEDs

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Stability of the object's composition

If reference LED operates continuously at high current density, then reference signal stability is improved, but reference LED lifetime decreases

Engineering Contradiction:

Improvereference signal stabilityVSAvoidreference LED lifetime

Core Design Contradiction:

Stability of the object's compositionVSDuration of action of stationary object

Solution Approach 1:

The reference LED is driven periodically rather than continuously, allowing it to rest between measurement cycles. This periodic operation reduces cumulative stress and heat generation, extending the reference LED's lifetime while still providing sufficient reference signals for brightness monitoring

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The reference LED's operating conditions are dynamically adjusted based on measurement needs. It operates at higher current density only when reference measurements are required, and at lower or zero current density during normal illumination periods, optimizing both reference signal stability and component longevity

Inventive Principle:

Principle #15Dynamics

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 fixed brightness over the lifetime of the LED lamp, reducing the need for expensive photo-detector based systems and minimizing the impact of temperature and operational variations, while extending the longevity of the reference LED.

Implementation Method 1

utilize LEDs (light emitting diode) as reference light sources

Methodology Applied

Scientific EffectLight Emitting Diode: Light Emitting Diode

Implementation Method 2

one or more illumination LEDs that are configured to provide illumination for the device

Methodology Applied

Scientific EffectLight Emitting Diode: Light Emitting Diode

Data Source

PatentUS8749172B2Luminance control for illumination devices

Publication Date: 2014.06.10 LUTRON TECHNOLOGY COMPANY LLC

AI summary

An illumination device is provided having one or more illumination LEDs configured to provide illumination for the device. Along with the illumination LED is a reference LED. The illumination LED provide illumination during normal operation of the device, whereas the reference LED provides a reference illumination, but does not provide illumination during normal operation. A light detector can detect light from the illumination LED and the reference LED, and control circuitry can be used to compare light detected from the reference LED and the illumination LED to adjust a brightness for the device. The light detector can comprise a photo-detector or can comprise an LED, such as one of the illumination LEDs if more than one illumination LED is utilized. A method is also provided for controlling brightness of an illumination device.