Incandescent Light Bulb

Introduction to light bulb:

     The light bulb is one of the wonders of the modern world.  The light bulb is an electric light source that’s technically called a lamp.  The most common type of “lamp” or bulb is the incandescent light bulb. These types of light bulbs are the oldest and simplest form of bulb technology, dating back to Thomas Edison’s experiments with filament types back in 1879.

History of Incandescent Lamp:

     It is normally considered that Thomas Edison was the inventor of the incandescent lamp, but the actual history was not like that. There were numbers of scientists who worked and designed prototype for the incandescent lamp before Edison did. One of them was British physicist Joseph Wilson Swan. From the record, it is found that he got the first patent for the incandescent lamp. Later Edison and Swan merged to produce incandescent lamps in commercial scale.

Construction of Incandescent Lamp:

     The filament is attached across two lead wires. One lead wire is connected to the foot contact and other is terminated on the metallic base of the bulb. Both of the lead wires pass through glass support mounted at the lower middle of the bulb. Two support wires also attached to glass support, are used to support filament at its middle portion. The foot contact is isolated from metallic base by insulating materials. The entire system is encapsulated by a colored or phasphare coated or transparent glass bulb. The glass bulb may be filled with inert gases or it is kept vacuum depending upon rating of the incandescent lamp.

     The filament of incandescent lamps is air-tightly evacuated with a glass bulb of suitable shape and size. This glass bulb is used to isolate the filament from surrounding air to prevent oxidation of filament and to minimize convention current surrounding the filament hence to keep the temperature of the filament high.

     The glass bulb is either kept vacuum or filled with inert gases like argon with a small percentage of nitrogen at low pressure. Inert gases are used to minimize the evaporation of filament during service of the lamps. But due to convection flow of inert gas inside the bulb, there will be greater chances of losing the heat of filament during operation.

     Again vacuum is a great insulation of heat, but it accelerates the evaporation of filament during operation. In the case of gas-filled incandescent lamps, 85% of argon mixed with 15% of nitrogen is used. Occasionally krypton can be used to reduce filament evaporation because the molecular weight of krypton gas is quite higher.

     But it costs greater. At about 80% of atmospheric pressure, the gasses are filled into the bulb. Gas is filled in the bulb with the rating more than 40 W. But for less than 40 W bulb; there is no gas used.

How Incandescent Bulbs Work?

     An incandescent bulb works on the principle of incandescence, a general term meaning light produced by heat.

     In an incandescent type of bulb, an electric current is passed through a thin metal filament, heating the filament until it glows and produces light.

     Incandescent bulbs typically use a tungsten filament because of tungsten’s high melting point. A tungsten filament inside a light bulb can reach temperatures as high as 4,500 degrees Fahrenheit. A glass enclosure, the glass “bulb”, prevents oxygen in the air from reaching the hot filament. Without this glass covering and the vacuum it helps create, the filament would overheat and oxidize in a matter or moments.

     After the electricity has made its way through the tungsten filament, it goes down another wire and out of the bulb via the metal portion at the side of the socket. It goes into the lamp or fixture and out a neutral wire.

Life Span of Incandescent Lamps:

     Whatever may be the technology of manufacturing, each type of incandescent lamps has some approximate life span. This is because of filament evaporation phenomenon which can be minimized but can not be avoided completely.

     Due to filament evaporation, the glass bulb darkens over a period. Due to filament evaporation the filament becomes thinner which makes the filament less luminous efficient and at last, the filament is broken. As the filament lamps are directly connected to the power supply line, the voltage fluctuations in the line, affect the performance of the bulb.

     It is found that luminous efficacy of an incandescent lamp is directly proportional to the square of supply voltage but at the same time, the life span of the lamp is inversely proportional to 13th to 14th power of supply voltage. The main advantages of incandescent lamps are that these are cheap enough and very suitable for lighting at small areas. But these lamps are not energy efficient and about 90% of input electrical energy is lost as heat.

Incandescent light bulb pros and cons:

     If you’re considering using incandescent bulbs, here are some pros and cons to consider.

Incandescent light bulb pros:

• Quality of light
  
  
  These bulbs are as close to the gold standard (the sun) as you can get.
  
  
• Affordability
  
  
  Looking to stay under your monthly light bulb budget? Pop a few incandescent bulbs in your sockets and let someone else take care of the utility bills.
  
  
• Aesthetics
  
  
  Even the lighting industry itself can’t deny that the aesthetics of a Incandescent light bulb are hard to beat. Heck, LED manufacturers have spent years just trying to figure out how to make an LED bulb that resembles a classic incandescent.
  
  
• Dimmability
  
  
  Incandescents are also the gold standard for dimmability. They don’t flicker or emit worse light when paired with a dimmer switch, like some products using other lighting technologies. The LED industry is working overtime just to make something that can dim like an incandescent.

Incandescent light bulb cons:

• Short life
  
  
  If your lighting maintenance bill is out the roof, incandescent bulbs aren’t going to help. You’ll be replacing them every 3-5 months, assuming 8-10 hours of burn time a day.
  
  
• Energy consumption
  
  
  As I said earlier, 90 percent of the energy used to make incandescent light is actually converted to heat. And if you aren’t wanting your light sockets to double as space heaters, you’re going to have to crank up your AC bill to compensate for the collective heat emitted from your incandescent light bulbs.
  
  
• Option limitations
  
  
  Compared to LEDs, incandescent bulbs are very limited in their color temperatures, lumen output, directionality, and other specifications that help to customize lighting today.