LED Illumination Apparatus Uniform Dim Mode Control
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Solution Overview
Problem
LED illuminations exhibit non-uniform behavior in dim mode, leading to some LEDs being activated successively rather than simultaneously, resulting in inhomogeneous brightness and an unpleasant appearance, known as the 'factory hall effect', due to insufficiently deterministic behavior at low luminous power.
Innovation Solution
An illumination apparatus with a control device that uses individual offset values for each LED group to derive an absolute dim drive value from a common nominal dim drive value, ensuring all LEDs are activated simultaneously and uniformly in dim mode by modifying the nominal dim drive value with offset values tailored to each group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common nominal dim drive value is used to drive multiple illumination units, then the control structure is simplified, but non-uniform activation of LEDs occurs in dim mode
Solution Approach 1:
The patent applies local quality by assigning individual offset values to each illumination unit or LED group. This allows each unit to have customized activation characteristics while still responding to a common control signal. The offset values compensate for manufacturing tolerances and threshold variations, ensuring uniform activation across all LEDs in dim mode without requiring complex individual control circuits for each LED.
2Reliability
If individual offset values are assigned to each LED group, then uniform activation is achieved, but the device complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-calculating and storing offset values for each illumination unit during manufacturing or initial setup. These offset values are stored in memory and automatically applied when dim mode is activated. This approach eliminates the need for real-time calculations or complex control algorithms during operation, achieving uniform LED activation while maintaining simple runtime control logic.
3Use of energy by moving object
If LEDs are operated in dim mode with low luminous power, then energy consumption is reduced, but non-uniform behavior and inhomogeneous brightness occur
Solution Approach 1:
The patent applies parameter changes by modifying the drive value parameter individually for each illumination unit through the addition of offset values. This adjustment compensates for the non-linear threshold behavior of LEDs at low current levels, ensuring that all LEDs reach their activation threshold simultaneously even when operated at reduced power levels in dim mode, thereby maintaining brightness uniformity while reducing energy consumption.
Data Source
AI summary
An illumination apparatus having a first illumination unit and a second illumination unit is provided. Each illumination unit has an LED arrangement and a supply device. Each LED arrangement has at least one LED group having a multiplicity of LEDs. A control device for driving the at least two illumination units with a common nominal dim drive value is included. The nominal dim drive value drives the illumination units in such a way that the similar LED groups of the illumination units are operated in a dim mode. The apparatus also has an offset device, which is formed to derive an absolute dim drive value for each of the similar LED groups from the nominal dim drive value with an offset value. The offset value is selectively assigned to the LED group and selected, such that the LED group is activated by the absolute dim drive value.