LED Chromaticity Control via Duty Cycle and Temperature Models
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Solid state lighting systems face challenges in achieving consistent color rendering due to variations in individual LEDs, leading to unnatural color representation in illuminated objects, especially with limited red spectrum emission in white LED backlights for LCD screens.
Innovation Solution
A method and apparatus for controlling solid state lighting devices by adjusting the duty cycle of LEDs based on temperature and current levels using models with Bézier surfaces to achieve target chromaticity, allowing for real-time adjustments to maintain desired color points and intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If white LED lighting devices with blue-emitting LED and wavelength conversion phosphor are used, then energy efficiency is improved, but color rendering quality deteriorates due to limited red spectrum emission
Solution Approach 1:
The patent combines multiple light emitting devices with different spectral characteristics (blue LED with yellow phosphor, red LED, green LED) into a single lighting system. This merging of different light sources allows the system to maintain the energy efficiency of LEDs while achieving comprehensive spectral coverage for natural color rendering, directly resolving the contradiction between energy efficiency and color rendering quality.
Solution Approach 2:
The lighting system uses composite phosphor materials including yellow phosphor converted from blue light and red phosphor materials that convert blue or green light to red wavelengths. This composite approach creates a multi-spectral light output that maintains LED energy efficiency while achieving full spectrum coverage for accurate color rendering.
2Ease of manufacture
If individual LEDs with variations are used in solid state lighting arrays, then manufacturing ease is improved, but color consistency deteriorates
Solution Approach 1:
The control system dynamically adjusts operating parameters (current levels, duty cycles) of individual LEDs based on their specific characteristics and environmental conditions (temperature, aging). This parameter adjustment compensates for variations between individual LEDs, maintaining color consistency while allowing the use of LEDs with natural manufacturing variations.
Solution Approach 2:
The system incorporates sensors that continuously monitor the actual color output and provide feedback to the control system. The controller uses this feedback to adjust the operation of individual LEDs in real-time, compensating for variations and maintaining consistent color output across the entire lighting array, thus resolving the contradiction between manufacturing ease and color consistency.
3Measurement precision
If duty cycle adjustment based on temperature and current models is implemented, then color control precision is improved, but system complexity increases
Solution Approach 1:
The system pre-characterizes each LED during manufacturing by measuring its color output at different current levels and temperatures, storing this data in lookup tables. During operation, the controller retrieves pre-calculated duty cycle values from these tables based on current temperature and current conditions, achieving precise color control without requiring complex real-time calculations, thus balancing precision with manageable system complexity.
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 enables precise control of LED lighting systems to produce consistent and natural color representation by compensating for variations in LEDs, improving color rendering index and overall lighting quality.
Implementation Method 1
a solid state light emitting device generates light through the recombination of electronic carriers, i.e. electrons and holes, in a light emitting layer or region
Implementation Method 2
white LED lighting devices that include a blue-emitting LED coated with a wavelength conversion phosphor that converts some of the blue light emitted by the LED into yellow light
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A solid state lighting apparatus includes a first plurality of light emitting devices configured to emit light when energized having a first chromaticity, a second plurality of light emitting devices configured to emit light when energized having a second chromaticity, different from the first chromaticity, and a controller configured to control a duty cycle of current supplied to the first plurality of light emitting devices. The controller is configured to control the duty cycle of the first plurality of light emitting devices in response to a change in a plurality of operating conditions of the solid state lighting apparatus in accordance with a model of the duty cycle that relates the duty cycle of the first plurality of light emitting devices to the plurality of operating conditions of the solid state lighting apparatus for a target light output characteristic of the solid state lighting apparatus. Related methods are also disclosed.