Blue-Red LED Current Balancing for Stable Warm White Light
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Solution Overview
Problem
Conventional LED lighting devices experience color shift due to different temperature-dependent radiant flux drops between blue and red LEDs, leading to inconsistent white light output as temperature changes.
Innovation Solution
A solid-state lighting device using a combination of blue and red LEDs connected in series with balancing resistors to maintain load balance and redistribute current passively, compensating for flux losses and maintaining warm white light within a predefined color temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blue LED and red LED are placed in the same package to generate warm white light, then color appearance is enhanced, but color shift occurs due to different temperature-dependent radiant flux drop
Solution Approach 1:
The patent implements a feedback mechanism where temperature sensors monitor the operating temperature of the LED package, and this temperature information is used to adjust the drive currents to blue and red LEDs dynamically. This closed-loop control compensates for the different temperature-dependent flux drops, maintaining stable color appearance across varying temperatures.
Solution Approach 2:
The patent changes the electrical parameters (drive currents) of the blue and red LEDs based on operating conditions. By adjusting the relative intensities of blue and red LED emissions through parameter modification, the system compensates for temperature-induced color shifts and maintains consistent warm white light output.
2Illumination intensity
If multiple LED strings are used to achieve desired brightness, then illumination intensity is improved, but load balance becomes difficult to maintain under temperature fluctuation
Solution Approach 1:
The control system continuously monitors the performance and temperature of each LED string, using feedback signals to adjust drive currents dynamically. This ensures that load is redistributed appropriately among parallel strings under varying temperature conditions, maintaining both brightness and load balance.
Solution Approach 2:
The patent transitions from static current distribution to dynamic current adjustment. The drive currents to multiple LED strings are made adjustable and adaptive based on real-time temperature and performance data, allowing the system to maintain optimal load balance across different operating conditions.
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 effectively minimizes color shift and maintains warm white light output by automatically adjusting current distribution between blue and red LEDs in response to temperature fluctuations, ensuring consistent color rendering across varying temperatures.
Implementation Method 1
An LED is a semiconductor diode with a biased p-n junction capable of emitting narrow-spectrum light or electroluminescence
Implementation Method 2
To convert blue light into the light with longer wavelength such as in the yellow or red region(s), luminescent materials such as phosphor material can be added
Implementation Method 3
A balancing resistor coupled to a string is configured to provide load balance and current redistribution between the strings in response to temperature fluctuation
Data Source
AI summary
A lighting device capable of generating warm or neutral white light using blue light-emitting diodes (“LEDs”), red LEDs, and/or luminescent material that responds to blue LED emission is disclosed. The lighting device includes multiple first solid-state light-emitting structures (“SLSs”), second SLSs, and balancing resistor element. The first SLS such as a string of blue LED dies connected in series is able to convert electrical energy to blue optical light, which is partially turned into longer wavelength emission by the luminescent material. The second SLS such as a red LED die is configured to convert electrical energy to red optical light, wherein the second SLSs are connected in series. While the first SLSs and second SLSs are coupled in parallel, the balancing resistor element provides load balance for current redistribution between the first and second SLSs in response to fluctuation of operating temperature.