ELE Times December 2016 Electronics News in India | Online Electronics Mag | Page 23

Cover Story

The Technology of LED Filaments
One of the advantages of filaments is that
the LEDs can be configured for omnidirectional light, the same as an
incandescent lamp. The 360 degrees flux
geometry has been missing in most LED
lamps available in the market today.
LED filaments lead to higher efficiencies
through the use of more LED emitters
from lower driving currents. LED Filaments
are upto 40pc more efficient than
traditional LED solutions and can provide
efficacy of 150lm/W.
Besides being Environmentally Friendly
(Mercury Free, Lead Free and RoHS
Compliant), LED Filament bulbs are also
Application Friendly (UV Free and IR Free).
Most LED Filament bulbs are dimmable
and Omni Directional.
The LED filament is composed of a series
of LEDs on a transparent substrate,
referred to as Chip-On-Glass (COG). The
substrate transparency allows the emitted
light to disperse evenly and uniformly
without any interference. An even coating
of phosphor in a silicone resin binder
material converts the blue light generated
by the LEDs into a mixture of red, blue,
and green light to create a specified light
temperature.
The LED filament can be made with
sapphire, glass, and transparent ceramic
substrates. Metal substrate LED filaments
are rarely seen on the market. Even
though glass substrates are less costly, the
filament has very low thermal dissipation.
Filament bulb designs are therefore
restricted by glass filament’s thickness of 1
mm to 2 mm. In comparison, sapphire
substrates are thinner with a substrate
thickness of 0.8 mm to 1 mm. Moreover,
its quality matches transparent ceramic
substrates, yet it is still slightly more costly
than glass. Sapphire substrate’s
comprehensive supply chain has made it
the most prominent filament material
found in LED filament bulbs, taking up
70pc to 80pc market share. Trailing in

second is transparent ceramic substrate
filaments 20pc market share, followed by
glass filaments mere 10pc.
The LED filament is then encapsulated in a
resin made up of a silicone and phosphor
mixture that transforms the LED chips’
blue light into white light. This design
allows the use of both blue LEDs as well as
red LEDs to modulate the color
temperature. Most manufacturers rely
solely on the phosphor to set the color
temperature.
Filament LED designs achieve even better
performance than their traditional LED
lamp counterparts by under driving many
smaller, low power LED chips. The result is
less heat, better efficacies, and sleeker
designs with no heat sink needed.
The high voltage-low current scheme is an
ideal combination for controlling the heat.
One of the novel approaches to thermal
management is to use a special gas
mixture inside the glass lamp to facilitate
the heat transfer to the glass surface more
efficiently.
MLS is a significant player in the LED
Filaments business with dedicated
manufacturing facility for Filament Bulbs
in China. We are supplying LED Filaments
as well as Private Branded bulbs to
multiple customers across the world and
are upgrading our manufacturing facilities
for lager production capabilities.
Conclusion
With aesthetic appeal and significant
performance advantages, LED filament
bulbs represent a flawless intersection of
form and function — vintage look and
advanced engineering. Coupled with the
market projections for the coming years,
LED Filament Bulbs are surely the next
generation in the evolution of LED
Lighting.

ELE Times | 23 | December, 2016