LED Chromaticity Stabilization During Dimming
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Solution Overview
Problem
Dimming solid state lighting systems cause changes in the chromaticity of light output, which is undesirable, and existing technologies are inefficient in utilizing LEDs with chromaticities outside standard bins for white light emission.
Innovation Solution
A light emitting apparatus comprising a combination of light emitting devices with specific chromaticity points, including phosphor-coated blue light emitting devices, that emit light within a 7-step MacAdam ellipse around the black body locus, allowing for a correlated color temperature between 2700K and 6500K, and a method of forming this apparatus using a substrate with a current supply and resistor configuration to maintain consistent chromaticity during dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phase cut dimming is used to reduce RMS voltage, then power consumption and light output are reduced, but chromaticity changes occur in solid state lighting systems
Solution Approach 1:
The patent implements dynamic current adjustment through multiple current sources that can be independently controlled. The system dynamically switches between different current levels (first current level for first LEDs, second current level for second LEDs) to maintain consistent chromaticity while dimming, rather than using static phase cut dimming that causes chromaticity shifts.
Solution Approach 2:
The patent changes the electrical parameters by providing separate current sources with different current levels to different LED groups. This parameter control allows maintaining optimal current through the incandescent bulb while adjusting current through LEDs to compensate for chromaticity changes, thereby stabilizing overall chromaticity during dimming operations.
2Ease of manufacture
If LEDs with chromaticity outside standard bins are used, then device complexity and manufacturing cost are reduced, but chromaticity consistency deteriorates
Solution Approach 1:
The patent applies local quality by dividing LEDs into different groups (first LEDs and second LEDs) with different chromaticity characteristics, and providing each group with tailored current levels. This allows LEDs with varying chromaticities (including those outside standard bins) to be utilized effectively while maintaining overall chromaticity consistency through differential current control.
Solution Approach 2:
The patent changes operational parameters by adjusting current levels differently for different LED groups. By controlling the second current level for second LEDs (with chromaticity outside standard bins) separately from the first current level for first LEDs, the system compensates for chromaticity variations and maintains consistent overall chromaticity output.
3Stability of the object's composition
If incandescent bulb is added to LED assembly, then chromaticity consistency is improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality by using the incandescent bulb not only as a light source but also as a chromaticity stabilization element. The bulb's inherent properties (positive temperature coefficient, spectral characteristics) are leveraged to compensate for LED chromaticity shifts during dimming, making the system self-regulating without requiring complex external control mechanisms.
Solution Approach 2:
The system achieves self-service through the incandescent bulb's natural electrical characteristics. The bulb's positive temperature coefficient automatically adjusts its resistance based on temperature, and its spectral output naturally compensates for LED chromaticity changes, providing self-regulating chromaticity stability without requiring external sensors or complex control circuits.
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 maintains a consistent warm white light output that mimics incandescent dimming characteristics, expanding the range of usable LEDs and improving efficiency in lighting applications by utilizing LEDs previously considered outside acceptable chromaticity ranges.
Implementation Method 1
phosphor-coated blue light emitting devices that emit light within a 7-step MacAdam ellipse around a point on the black body locus
Implementation Method 2
phosphor-coated blue light emitting devices
Implementation Method 3
utilizing a shunt resistor to mimic incandescent dimming characteristics
Data Source
AI summary
A light emitting apparatus includes a first light emitting device configured to emit light having a first chromaticity point that falls within a region on a 1931 CIE Chromaticity Diagram defined by points having coordinates (0.32, 0.40), (0.36, 0.48), (0.43, 0.45), (0.42, 0.42), (0.36, 0.38), and at least two second light emitting devices, each of the at least two second light emitting devices emits light having a respective second chromaticity points that that have ccx values greater than 0.4077 and ccy values less than 0.3944 on the 1931 CIE Chromaticity Diagram. A combined light emitted by the first light emitting device and the at least two second light emitting devices has a third chromaticity point that falls within a 7-step MacAdam ellipse around a point on the black body locus having a correlated color temperature between 2700K and 6500K. The third chromaticity may shift to a more reddish chromaticity when power supplied to the light emitting devices is decreased.