LED filament

A 230-volt LED filament light bulb, with a B22 base. The filaments are visible as the four yellow vertical lines.

An LED filament light bulb is an electric light bulb which produces light with a LED that is designed to resemble the filament of an incandescent light bulb, sometimes an Edison light bulb. The bulb also feature the exact same design as a conventional incandescent light bulb.

History and design

A LED filament type design light bulb was produced by Ushio Lighting in 2008,[1] intended to mimic the appearance of a standard light bulb.[2] Contemporary bulbs typically used a single large LED or matrix of LEDs attached to a large heatsink. As a consequence, these bulbs typically produced only a 180 degree range of light.[2] By the mid 2010s, LED filaments were being introduced into the market by several manufacturers. These designs used several LED filament light producers arranged in the same or similar pattern to that found in the wires of a standard incandescent bulb.[2]

The LED filament is composed of a series of LEDs on a transparent substrate, referred to as Chip-On-Glass (COG). These transparent substrates are made of glass or sapphire materials. This transparency allows the emitted light to disperse evenly and uniformly without any interference. An even coating of yellow phosphor in a silicone resin binder material converts the blue light generated by the LEDs into white light.[2] Degradation of silicone binder, and leakage of blue light are design issues in LED filament lights. Positive benefits of the LED design are potential higher efficiencies by the use of more LED emitters from lower driving currents. A major benefit of the design is the ease with which near full "global" illumination can be obtained from arrays of filaments.[2]

Lifespan of LED emitters is reduced by high operating temperatures. In the absence of a heat sink, LED filament bulbs may use a high thermal conductivity gas inside the bulb to aid heat dissipation.[2]

The large number of LEDs (typically 28 per filament) simplifies the power supply compared to traditional LEDs as the voltage per blue LED is 2.48 < ΔV < 3.7. Some types may additionally use red LEDs (1.63 < ΔV < 2.03). Two filaments with a mix of red and blue is thus close to 110 V, or four close to 220 V to 240 V, compared to the 3 V to 12 V needed for a traditional LED lamp. Typically, four filaments are used and the appearance is similar to an overrun carbon filament lamp. Typically, a mix of phosphors are used to give better colour rendition (which is a separate issue to colour temperature) than the early blue LEDs with yellow only phosphor.

LED filament lamps are patented.[1][3][4]

References

  1. 1 2 US 2009184618, Kunihiko Hakata & Tomomi Matsuoka, "Light-emitting device and lighting apparatus incorporating same", published 2009-07-23, assigned to Ushio Denki KK
  2. 1 2 3 4 5 6 Lin, Judy (5 Feb 2015). "The Next Generation of LED Filament Bulbs.". www.ledinside.com.
  3. ↑ Wu, Bor-jen. "LED LIGHT BULB". US Patent office. Retrieved 2015-01-04.
  4. ↑ Feng, Yunglong. "LED LIGHT AND FILAMENT THEREOF". US Patent office. Retrieved 2015-01-04.
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