Solid State Lighting Chromaticity Control via Segmented LED Bypass
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Solution Overview
Problem
Solid state lighting systems face challenges in accurately reproducing color across a wide range of dimming levels, particularly in following the Planckian locus, as conventional systems tend to produce light that appears too red when dimmed below 1800K, due to variations in LED manufacturing and binning techniques.
Innovation Solution
Incorporating additional LED segments, such as amber LEDs, that emit an additional v′ component to shift the chromaticity of the combined light towards the Planckian locus, allowing the lighting apparatus to maintain a consistent color temperature across a wider range of dimming levels by modulating current through different LED segments using a control circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional LED systems are dimmed below 1800K, then energy efficiency is improved, but color accuracy deteriorates (light appears too red and deviates from Planckian locus)
Solution Approach 1:
The LED system is divided into multiple segments with different chromaticity characteristics (e.g., first LED segment with cooler color temperature, second LED segment with warmer color temperature). By independently controlling the brightness of each segment, the system can maintain accurate color rendering at low brightness levels while preserving energy efficiency benefits.
Solution Approach 2:
The system dynamically changes the chromaticity parameters of the emitted light by adjusting the relative contribution of different LED segments. As the overall brightness decreases, the system shifts the color temperature parameters to follow the Planckian locus more accurately, preventing the redshift that occurs in conventional single-temperature LED systems.
2Manufacturing precision
If additional LED segments are added to improve color accuracy across dimming ranges, then color rendering is improved, but device complexity increases
Solution Approach 1:
The LED array is segmented into multiple independently controllable groups, each with distinct chromaticity properties. This segmentation allows the system to achieve superior color accuracy across the full dimming range by selectively activating appropriate segments, while the modular structure keeps the control architecture manageable.
Solution Approach 2:
The additional LED segments serve multiple functions: they provide color temperature adjustment, enable Planckian locus following, and maintain energy efficiency. This multi-functionality justifies the increased device complexity by delivering multiple performance benefits simultaneously rather than requiring separate systems for each function.
3Adaptability or versatility
If multiple LED segments with different chromaticities are used, then adaptability across dimming levels is improved, but control complexity increases
Solution Approach 1:
The control system dynamically adjusts the brightness ratio between different LED segments based on the desired overall brightness level. At higher brightness levels, cooler segments dominate; as brightness decreases, warmer segments are progressively activated to maintain Planckian locus adherence. This dynamic adaptation enables versatile dimming performance with a control strategy that scales with brightness requirements.
Solution Approach 2:
The control circuit incorporates feedback mechanisms to monitor the actual chromaticity output and adjust segment brightness ratios accordingly. This feedback ensures that the system maintains accurate color rendering across the entire dimming range, adapting to variations in LED aging, temperature, and manufacturing tolerances while managing control complexity through closed-loop regulation.
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 enables solid state lighting systems to produce light that closely follows the Planckian locus over a broader dimming range, providing a more natural and consistent color temperature similar to incandescent lighting, even at lower brightness levels.
Implementation Method 1
A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs)
Implementation Method 2
modulate the at least one additional bypass circuit to cause the lighting apparatus to emit an additional v′ shift in a chromaticity value of light emitted by the string
Data Source
AI summary
A solid state lighting apparatus can include a plurality of light-emitting devices (LEDs) that are electrically coupled together in at least one string. The apparatus can further include a first LED segment that is configured to emit a first chromaticity light coupled across a first bypass circuit, a second LED segment that is configured to emit a second chromaticity light coupled across a second bypass circuit, and at least one additional LED segment that is configured to emit an additional chromaticity light coupled across a respective at least one additional bypass circuit. A control circuit can be configured to modulate the at least one additional bypass circuit, to cause the lighting apparatus to emit an additional v′ shift in a chromaticity value of light emitted by the string to vary substantially in conformance with a Planckian locus in response to a dimming input to the control circuit.