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How LED bulbs are made

Posted by lexifip158 on June 17th, 2020


One hundred and thirty years ago, Thomas Edison completed the first successful sustained test of the incandescent light bulb. With some incremental improvements along the way, Edison's core technology has lit up the world ever since. This is about to change. We are on the cusp of a semiconductor-based lighting revolution that will eventually replace Edison's bulbs with a much more energy efficient lighting solution. Solid state LED lighting will eventually replace almost all of the hundreds of billions of incandescent and fluorescent lights currently in use worldwide. In fact, as a step on this path, President Obama last June introduced stricter new lighting standards that will support the phasing out of incandescent light bulbs (which are already banned in some parts of Europe).

To understand how revolutionary LED bulbs are and why they are still expensive, it is instructive to look at how they are made and compare this to the manufacture of incandescent bulbs. This article explores how incandescent bulbs are made and then contrasts that process with a description of the typical LED bulb manufacturing Lucid™.

So, let's start by looking at how traditional incandescent bulbs are made. You will find this to be a classic example of a refined automated industrial process in over a century of experience.

While individual incandescent bulb types differ in size and wattage, they all have the three basic parts: the filament, the bulb, and the base. The filament is made of tungsten. Although very fragile, tungsten filaments can withstand temperatures of 4,500 degrees Fahrenheit and above. The connection or input cables are generally made of nickel-iron wire. This cable is immersed in a borax solution to make the cable more adherent to the glass. The bulb is made of glass and contains a mixture of gases, usually argon and nitrogen, which increase the life of the filament. Bulb air is pumped in and replaced with gases. A standardized base keeps the whole set in place. The base is known as the "Edison screw base". Aluminum is used on the outside and glass to insulate the inside of the base.

Originally produced by hand, light bulb manufacturing is now almost fully automated. First, the filament is manufactured using a process known as drawing, in which the tungsten is mixed with a binder material and pulled through a die (a shaped hole) on a fine wire. The wire is then wound around a metal rod called a mandrel to mold it into its proper coiled form, and then heated in a process known as annealing, smoothing the wire and making its structure more uniform. The mandrel dissolves in acid.

Second, the wound filament is attached to the input cables. The input cables have hooks at their ends that are pressed onto the end of the filament or, in larger bulbs, spot welded.

Third, light bulbs or glass covers are produced using a tape machine. After heating in an oven, a continuous glass belt is moved along a conveyor belt. Precisely aligned air nozzles blow the glass through holes in the conveyor in molds, creating the housings. A treadmill machine moving at maximum speed can produce more than 50,000 light bulbs per hour. After blowing the casings, they are cooled and then cut from the tape machine. The inside of the bulb is then coated with silica to remove glare caused by an exposed, shiny filament. The label and stem are stamped on the outer top of each case.

Fourth, the base of the bulb is also built with molds. It is made with screw-shaped grooves so that it can easily fit into the socket of a lamp.

Fifth, once the filament, base and bulb are made, the machines put them together. First, the filament is mounted on the stem assembly, with its ends attached to the two input cables. Then the air inside the bulb is evacuated, and the housing is filled with the mixture of argon and nitrogen.

Finally, the base and the bulb are sealed. The base slides over the end of the glass bulb so that no other material is needed to hold them together. Instead, their conformal shapes allow the two pieces to be held together, with the input cables touching the aluminum base to ensure proper electrical contact. After testing, the bulbs are placed in their packages and shipped to consumers.

Also See: Input Cables, Light Bulbs, Led Bulbs, Incandescent Bulbs, Made, Filament, Bulbs

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