LED Light Source With Series Resistor for Dimming Color Shift
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Solution Overview
Problem
LED light emitting devices with fixed color temperature do not match the varying color temperature of incandescent lamps when both are used together, causing a sense of incongruity, especially under dimming conditions.
Innovation Solution
A light emitting device using two LEDs in parallel, one emitting red light and the other white light, with a resistor in series with the red LED to alter their current-voltage characteristics, allowing the color temperature to change with luminous flux, mimicking the behavior of incandescent lamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LEDs of different colors are used to achieve adjustable color temperature, then color temperature can be freely set, but the luminous flux-color temperature property becomes uniform unlike incandescent lamps
Solution Approach 1:
The patent applies local quality by assigning different forward voltage characteristics to different color LEDs through series resistors. The red LED has a lower forward voltage (with series resistor) compared to the white LED, creating localized electrical property differences that cause selective activation based on voltage level, thereby achieving variable color temperature with dimming
2Illumination intensity
If the same luminous flux is set to LED and incandescent lamp, then brightness is equal, but the color temperature of LED is different from incandescent lamp
Solution Approach 1:
The patent implements dynamics by making the color temperature of the LED light source variable rather than fixed. Through the voltage-dependent activation of different color LEDs (red at lower voltage, white at higher voltage), the color temperature dynamically changes with luminous flux level, matching the dynamic behavior of incandescent lamps
3Ease of operation
If a dimmer switch is used to control brightness, then brightness can be adjusted, but the luminous flux-color temperature property difference between LED and incandescent lamp becomes more apparent
Solution Approach 1:
The patent applies parameter changes by utilizing the voltage-current characteristics of different color LEDs combined with series resistors. As the operating voltage changes during dimming, the forward current distribution among LEDs changes, causing both luminous flux and color temperature to vary together, replicating the parameter coupling found in incandescent lamps
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 device achieves a luminous flux-color temperature property where the color temperature increases with brightness, matching the behavior of incandescent lamps, eliminating the incongruity when used with incandescent lamps and allowing seamless dimming control.
Implementation Method 1
a resistor which is connected in series to the first LED to make forward current changing characteristics of the first and the second LED depending on change in the operating voltage to be different from each other
Implementation Method 2
a first and a second light emitting diode (LED) which are connected in parallel to each other and emit lights of different colors, respectively
Implementation Method 3
light emitting diode (LED) which has low power consumption and a long lifespan draws great attention as a noticeable light source
Data Source
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Figure 3A~4
AI summary
A light emitting device includes: a light source unit which has a first and a second LED which are connected in parallel and emit lights of different colors, respectively. The lights of the first and the second LED are mixed to provide an emission light of the light source unit when an operating voltage is applied. The light source unit further has a resistor which is connected in series to the first LED to make forward current changing characteristics of the first and the second LED depending on change in the operating voltage to be different from each other, so that a required luminous flux-color temperature property, in which change in a color temperature of the emission light is made to depend on change in a luminous flux of the emission light, is obtained while the first and the second LED are turned on by applying the operating voltage.