• Incandescent Lamp
  • Halogen Lamp
• Gas-Discharge Lamps
  • Neon Lamp
  • Fluorescent Lamp
  • Compact Fluorescent Lamp

• Related Pages

This photo of an incandescent lamp with a clear envelope shows the filament glowing white hot.

This is one of the lamps in the vanity light in the bathroom of my sister's house. I took this picture Christmas day 2003. Thanks, Michele!

Modern incandescent lamps tend to have coiled filaments made from tungsten. The bulb envelope of most lamps is filled with an inert gas that keeps the hot filament from oxidizing, like argon, krypton, or nitrogen. In some special cases, the envelope is simply evacuated. This makes the lamp more efficient, but shortens the life of the lamp.

Even the simple "light bulb" lamp has many variations. Such lamps can be specified by their many characteristics:

• type and size of the base (electrical connector), which can be indicated several ways
• diameter of the glass envelope
• maximum overall length

For example, the common household "light bulb" in the United States uses an E26 screw base, and A19 envelope.

For more information on the many different characteristics, please see incandescent lamp specs.

For more information on the many different characteristics, please see incandescent lamp specs.

All forms of gas discharge lamp share an interesting characteristic: the electrical characterstics of the gas are nonlinear. In other words, the gas acts like an insulator, and a very high voltage is required to ionize it. But once the gas ionizes, it turns into an excellent conductor, and you can turn down the voltage. If you don't use a special power supply that limits the current, the power that is required to start up the lamp is too high to run it with.

• using a gas other than actual neon
• using colored or painted glass for the envelope
• addition of other materials, like mercury
• coating the inside of the glass envelope with phosphors, as in a fluorescent lamp

In modern practice, just about any color other than the orange-red of neon gas is actually produced by argon, mercury, and phoshors.

Neon lamps require a high voltage (15,000 Volts or more), with a ballast to limit the current when the arc is running. Traditionally, both jobs were performed by a special "neon sign transformer" or "luminous tube transformer", using a heavy iron core.

This is a traditional neon sign transformer. It puts out 12,000 Volts at 30 mA, and weight 19 pounds.

I also have a couple of smaller transformers that put out 3,000 Volts at 50-60 mA, and weigh 11.5 pounds apiece.

Nowadays, electronic power supplies are more efficient and lighter.

• The main body of the lamp constitutes a long electric arc, which ionizes the gas in the lamp to form a luminous plasma.
• Each end of the lamp tube contains an incandescent filament that heats up the lamp and emits electrons to kick-start the lamp.
• The tube contains a quantity of mercury. Ionized mercury vapor is an efficient way to make a lot of light, but much of it is ultraviolet.
• The inside surface of the tube is coated with a fluorescent phosphor that converts the ultraviolet to visible light.

Fluorescent lamps generally run warm to the touch, not hot. Different colors of light are easily generated by using different phosphors in the inner lamp coating.

Fluorescent lamps require a "ballast". It performs two functions: it provides the starting kick to ionize the gas in the fluorescent tube, and it limits current after the arc has been established.

Lamp manufacturers all use different systems to come up with their part numbers, and I won't attempt to list them. In addition to the manufacturer's part numbers, most lamps also have a semi-standard number on them. The semi-standard number usually takes one of these formats:

{type}{shape}{wattage}{color}-T{diameter}

{type}{shape}{wattage}T{diameter}-{color}

As was mentioned, the Tnn part of the number indicates the diameter of the glass tube in increments of 1/8-inch. Common values are:

T8	1"	2.54 cm
T12	1.5"	3.81 cm

The length of the tube is not encoded as part of the semi-standard number.

• The lamp tube is smaller in diameter and not as long.
• The smaller lamp tube is made even more compact by coiling the tube, or bending it into parallel loops.
• In order to get good light output from the smaller tube:
  • High-efficiency phosphors are used.
  • More mercury is used, to generate more ultraviolet, to be turned into more usable light.
• The circuitry necessary to drive the lamp is miniaturized and built into the base of the lamp itself.

Compact fluorescent lamps are often used as drop-in replacements (well, screw-in replacements) for incandescent lamps. In this application, compact fluorescents save power and last longer than the lamps they replace.

• introduction to lighting
• common light sources [this page]
• exotic light sources
• light emitting diodes (LEDs)
• generating and projecting black light
• incandescent lamp specs

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