LED Color Temperature Control via Current Distribution
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Solution Overview
Problem
Solid state lighting systems face challenges in maintaining consistent color temperature and color rendering index across varying brightness levels, as individual LEDs exhibit manufacturing variations, requiring complex binning and feedback mechanisms to achieve desired color points.
Innovation Solution
A lighting apparatus comprising serially-connected LEDs with different chromaticities, including blue-shifted yellow (BSY) and red LEDs, coupled with a control circuit that varies current distribution in response to dimming signals, allowing the color temperature to conform to the Planckian locus and maintain a high color rendering index (CRI) across brightness levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If individual LEDs with manufacturing variations are used, then device complexity is reduced, but color temperature consistency deteriorates
Solution Approach 1:
The patent applies parameter changes by varying the forward voltage characteristics of LEDs within a string. By selecting LEDs with different forward voltages and using a constant current source, the system achieves different current distributions across LEDs, which in turn produces varying color temperatures. This allows the lighting system to dynamically adjust color temperature without requiring complex feedback mechanisms or precise manufacturing tolerances.
2Stability of the object's composition
If feedback mechanisms are implemented to maintain color points, then color temperature consistency is improved, but device complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the system automatically adjusts color temperature based on the inherent variations in LED forward voltages. The constant current source naturally distributes current differently across LEDs with varying forward voltage characteristics, creating a self-regulating system that maintains color temperature consistency without requiring external feedback loops, sensors, or complex control algorithms.
3Use of energy by moving object
If brightness is reduced, then energy consumption is decreased, but color rendering index deteriorates
Solution Approach 1:
The patent applies dynamics by making the color temperature adjustable based on brightness levels. As the overall brightness decreases, the system dynamically shifts the color temperature to maintain optimal color rendering. This is achieved by exploiting the non-linear current distribution across LEDs with different forward voltages, where dimming the overall output automatically alters the relative contribution of different color LEDs, thereby preserving color rendering quality at lower energy consumption levels.
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 a lighting system that approximates incandescent lighting behavior by adjusting color temperature and maintaining high CRI from maximum to low brightness levels, providing a consistent and pleasing white light similar to incandescent bulbs.
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)
Data Source
AI summary
A lighting apparatus includes at least two sets of light-emitting devices with overlapping spectra and different chromaticities, such as two sets of blue-shifted yellow (BSY) LEDs producing outputs with different yellow content. The devices may be selectively controlled, e.g., by using selective current bypass circuits, to provide a desired color temperature or other visual performance in response to a dimming control input such that, for example, a light output approximating that of an incandescent lamp may be achieved.