PWM LED Stroboscopic Effect Mitigation via Asynchronous Timing
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Solution Overview
Problem
Pulse-modulated lighting systems, particularly those using LEDs, often exhibit a stroboscopic effect and 'beads' effect due to synchronous PWM operation, which are perceptible to the human eye and can be intensified by the instantaneous nature of LEDs, leading to undesirable flickering and discontinuous light perception.
Innovation Solution
The method involves coordinating the pulse-modulated pulses of LEDs so that a pulse of one LED falls within the switch-off time of another, either by placing it in the middle or aligning positive and negative edges, and optionally using amplitude modulation to maintain a constant time average, while synchronizing operating devices to a common time base, such as mains supply voltage zero crossings, to minimize stroboscopic effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LEDs are operated with synchronous PWM control at low dimming values, then energy consumption is reduced, but a stroboscopic effect occurs that is perceptible to the human eye
Solution Approach 1:
The patent divides the synchronous PWM control into asynchronous operation by assigning different duty cycles to individual LEDs or LED groups. This segmentation breaks the unified on/off pattern into staggered timing, eliminating the collective stroboscopic effect while preserving individual dimming functionality and energy savings.
Solution Approach 2:
The patent employs periodic PWM modulation with different frequencies or phase shifts for individual LEDs. By varying the periodic timing parameters asynchronously across multiple LEDs, the system maintains energy-efficient pulsed operation while preventing the regular, perceivable flicker pattern that causes stroboscopic effects.
2Device complexity
If multiple LEDs are controlled with the same PWM duty cycle, then control simplicity is maintained, but the stroboscopic effect is intensified due to synchronous switching
Solution Approach 1:
The patent introduces dynamic variation in PWM duty cycles across different LEDs or time periods. Instead of static synchronous control, the system dynamically adjusts individual LED timing parameters, creating asynchronous operation that eliminates stroboscopic effects while maintaining relatively simple control architecture through programmable parameters.
3Use of energy by moving object
If PWM frequency is reduced to extend on-time at low dimming values, then energy efficiency improves, but the stroboscopic effect becomes more pronounced due to longer off-periods
Solution Approach 1:
The patent segments the total off-period across multiple LEDs by staggering their duty cycles. While individual LEDs have extended off-times for energy efficiency, the collective lighting maintains continuous illumination because different LEDs are active at different times, preventing perceivable darkness periods and stroboscopic effects.
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 reduces the stroboscopic effect and prevents the 'beads' effect by ensuring continuous illumination and minimizing phases of zero light, thereby improving the visual perception of lighting systems and maintaining color stability.
Implementation Method 1
LEDs essentially instantaneously generate a light output proportional to the current flowing through them
Data Source
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AI summary
The invention discloses a method for the operation of LEDs lying in visual range of one another and being operated by PWM modulation. Said method aims to reduce the stroboscopic effect that would otherwise be visible to the human eye. According to the method, PWM pulses are temporally synchronised with each other such that the PWM pulse of a first LED occurs within the PWM off-period of another LED.