TRANSPARENT-COLOR LIGHT BULB
LED FILAMENT CHALLENGES

filament-comparison

SHAPE OF LED FILAMENT(S)
The current standard, single, vertically oriented linear LED filament design is starkly different from the more complex tungsten filament design of a 3-D “M” shape.

Solution:
Creating a custom shape: “Λ” would provide an improvement, but also create other challenges
(see: DARKER SIDE OF FILAMENT topic, below)

THICKNESS OF LED FILAMENT
The phosphor coating is ~ twice as thick as a tungsten filament. This creates a comparably reduced pin-point light effect, mostly with short range viewing of ~ 1.5 meters or less.

Solution:
No known solution. Explore possible advancements in micro LED filament design.
This alone is not seen as an unacceptable compromise. 

DARKER SIDE OF FILAMENT
The darkened transparent color reveals the orientation of the LED chips on the transparent sapphire substrate, creating a notable contrast from one half of the bulb to the other. The back side of the substrate appears more yellow, diffused and dull. The darker the colored coating, the more this is evident. NOTE: For reasons currently unknown to us, this is less of an issue with some LED filaments, including those used in our 2020 Tru-Tone bulbs

Solution:
-Use of a high-quality light transmissive substrate (sapphire) where the front/back variation is minimal.
-With the proposed “Λ” shape, it may be improved somewhat.

LED CHIP ORIENTATION DIAGRAM

filament-design-update3

It is currently conceivable that there are four ways to construct an LED filament of this shape.
(see: LED chip orientation diagram above)

 

One method (MODEL A) is to position the LED’s along the top of a cast/cut substrate in the desired “Λ” shape. This is considered to be the best effect from all viewing angles, the especially from the top or the cross-section side. The least effective view would be perpendicular to the inverted V shape, you would be looking directly at the side edge of the LED chips, where their appearance begins to appear more muted.

 

A second method (MODEL B) would be to cast/cut the substrate into the desired “Λ” shape with the flat side oriented outwards, and with the chips mounted along the face. This, however, creates an optimal view from only one side of the bulb, with suboptimal results from the top, two side and the rear of the bulb.

(It is unknown to us if there are filaments with LED’s mounted to both sides of the substrate. We believe the length of the filament is linked to its brightness, and would therefore require an unfavorable reduction in size.)

 

A third method (MODEL C) uses two standard filaments in shorter length, connected at the point of the “Λ” shape, and with the filaments flipped in opposing directions with their LED’s mounted on opposite sides. This method may prove easiest to manufacture while also creating a generally similar appearance from most angles.

 

A fourth method (MODEL D): similar to MODEL C using two standard short filaments welded together, but with the LED chips oriented upwards like MODEL A.
 

SAMPLES:

All samples specifically related to the filament should be in the correct color temperature ( 2200ºK ) and wattage (~0.54 – 0.64 watt). 
5 samples are requested:  2 C7 clear, 1 C7 ceramic-type in WHITE,  1 C7 interior satin-frost, 1 C9 clear.
Please inform prior to sample orders if there are any problems creating samples with these parameters. 

Satin-finish

Lastly, If it’s determined that a fully satisfactory transparent-color bulb option can not be achieved at present time,
an interior satin finish application may produce an acceptable alternative, possibly further improved as an E12 G30 bulb (pictured above).

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