CSP LED Filament Phosphor Layout for Low Yellow-Off Appearance
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Solution Overview
Problem
LED filament lamps with visible filaments exhibit a yellow color when off, which is unattractive in traditional or retro-styled lighting fixtures, and existing designs use excessive phosphor that affects the appearance.
Innovation Solution
Employ chip scale package (CSP) LEDs with a reduced amount of phosphor, using a thin conformal layer on the LED die surfaces and eliminating encapsulating phosphor to minimize the yellow color, combined with a compact filament geometry and transparent encapsulation for even light distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional LED filament design with encapsulating phosphor is used, then the phosphor provides complete light conversion and uniform appearance, but the yellow color is noticeable and unattractive when the bulb is off
Solution Approach 1:
The patent removes the traditional encapsulating phosphor layer that completely covered the LED chips. Instead, it applies phosphor only to specific surfaces (top and/or sidewalls) of the LED chips, extracting the harmful full-encapsulation while retaining the beneficial light conversion function where needed.
Solution Approach 2:
The patent applies phosphor selectively to specific locations on the LED chips rather than uniformly across all surfaces. The phosphor is applied to the top surface and/or sidewalls where it can still provide light conversion, but omitted from bottom surfaces that would otherwise contribute to yellow appearance when off.
2Object-affected harmful factors
If chip scale package LEDs with reduced phosphor are used, then the yellow color is minimized, but the light distribution uniformity may be affected
Solution Approach 1:
The patent applies phosphor to specific surfaces (top and/or sidewalls) of the LED chips to achieve local light conversion. This selective application reduces yellow color when off while maintaining sufficient light distribution uniformity through strategic phosphor placement on multiple surfaces of each chip.
Solution Approach 2:
The patent extends phosphor application from a single surface to multiple dimensions by applying it to both the top surface and sidewalls of the LED chips. This multi-surface approach maintains light distribution uniformity while reducing overall phosphor quantity and yellow appearance.
3Quantity of substance
If phosphor is applied only to LED chip surfaces without encapsulation, then the amount of phosphor is reduced and yellow color is minimized, but additional transparent encapsulant is needed for protection
Solution Approach 1:
The patent extracts and removes the traditional thick encapsulating phosphor layer, replacing it with a minimal transparent encapsulant that provides protection without the yellowing effect. This reduces phosphor quantity while using a different material for the protective function.
Solution Approach 2:
The patent changes the material parameter of the encapsulant from phosphor-based to transparent resin-based. This parameter change allows the encapsulant to provide protection and structural integrity without contributing to yellow color appearance when the bulb is off.
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 solution provides inconspicuous LED filaments that emit white light without a noticeable yellow hue, allowing integration into bulb designs that mimic traditional tungsten bulbs while maintaining efficient light distribution.
Implementation Method 1
Light emitting diode (LED) chips are engaged to the contact pads along the length of the metal stent substrate to provide that the LED chips are electrically connected in series
Implementation Method 2
each light emitting diode chip includes at least an upper surface that is in contact with an individual portion of phosphor
Data Source
AI summary
A light emitting filament diode that includes a filament substrate; a plurality of light emitting diodes (LEDs) electrically connected and disposed along a length of the filament substrate; and a phosphorus encapsulant present in direct contact with an upper surface and sidewalk of at least one of the plurality of light emitting diodes (LEDs). No portion of phosphorus encapsulant is present overlying a portion of the filament substrate extending between the sidewalls of adjacently situated light emitting diodes having phosphorus encapsulant present thereon. The light emitting filament diode may a include a transparent encapsulant present over at least the light emitting diode chips.