AC LED with Dual Long-Persistent Phosphors for Flicker Reduction
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Solution Overview
Problem
AC light emitting devices connected to alternating current power sources experience flicker effects due to phase changes, which can cause eye fatigue and visibility issues when used in moving objects, and existing solutions either increase costs or reduce light output by using additional circuits or limited amounts of long-persistent phosphors.
Innovation Solution
The use of two light emitting diode chips with different long-persistent phosphors, each performing wavelength conversion and having distinct afterglow luminescence, to alleviate flicker effects without additional circuits, while maintaining light output by varying the amount of phosphor used on each chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a delay unit circuit is added to prevent flicker, then flicker effect is reduced, but device complexity and cost increase
Solution Approach 1:
The patent extracts the flicker prevention function from the electrical circuit domain and transfers it to the optical domain by using long-persistent phosphor materials. Instead of adding a delay unit circuit to manipulate AC power phases, the invention uses phosphor's inherent long decay time to maintain continuous light emission, thereby eliminating the need for additional circuitry while preventing flicker effects.
Solution Approach 2:
The patent replaces the electrical/mechanical delay unit circuit with an optical solution based on phosphorescence. The long-persistent phosphor material naturally delays light emission through its extended decay time constant, substituting the need for active circuit control with passive optical material properties, thus reducing device complexity.
2Object-affected harmful factors
If long-persistent phosphor is used to reduce flicker, then flicker effect is alleviated, but light emission output is reduced due to increased phosphor loss
Solution Approach 1:
The patent optimizes the decay time parameter of the phosphor material, selecting long-persistent phosphors with decay times between 1ms and 1000ms. This parameter range is carefully chosen to provide sufficient afterglow for flicker prevention while minimizing energy loss. The invention also optimizes phosphor layer thickness and composition to balance persistence duration with light transmission efficiency.
Solution Approach 2:
The patent employs composite phosphor systems combining long-persistent phosphor materials with conventional phosphors. This composite approach allows the long-persistent phosphor to provide flicker-free operation during AC phase transitions while the conventional phosphor maintains high light emission efficiency during steady-state operation, thus achieving both flicker reduction and maintaining light output.
3Object-affected harmful factors
If amount of long-persistent phosphor is increased to further reduce flicker, then flicker effect is more reduced, but light emission output is reduced due to increased light loss
Solution Approach 1:
The patent applies long-persistent phosphor locally rather than uniformly throughout the entire phosphor layer. Specifically, the long-persistent phosphor is positioned in regions where it can most effectively prevent flicker (such as near the LED chip or in specific angular zones), while other regions use conventional phosphors for optimal light emission. This local application strategy prevents excessive light absorption while maintaining flicker-free operation.
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 effectively reduces flicker effects and maintains light output by utilizing different long-persistent phosphors on AC light emitting devices, preventing eye fatigue and visibility issues without increasing costs or reducing light emission.
Implementation Method 1
a first long-persistent phosphor disposed on the first light emitting diode chip to perform wavelength conversion of a portion of light emitted from the first light emitting diode chip
Implementation Method 2
an AC light emitting device adopting a long-persistent phosphor has been disclosed in Korean Patent No. 10-746952... emitting another light from the long-persistent phosphor which has a long decay time when the phases of the AC power change
Data Source
AI summary
An AC light emitting device includes a first light emitting diode chip and a second light emitting diode chip, each of which has a plurality of light emitting cells on a single substrate. A first long-persistent phosphor is positioned on the first light emitting diode chip to perform wavelength conversion for a portion of light emitted from the first light emitting diode chip, and a second long-persistent phosphor is positioned on the second light emitting diode chip to perform wavelength conversion for a portion of light emitted from the second light emitting diode chip. The afterglow luminescence period of the second long-persistent phosphor is different from that of the first long-persistent phosphor.