Incandescent Light Bulb Basics

The basic design of the incandescent lamp has not changed much since the late 1800s, when Thomas Alva Edison successfully produced the first operational electric light bulb. These are the must-know fundamental facts about incandescent lamps and the alternative choices that are available today.

KEY LIGHT BULB CHARACTERISTICS

Rated Voltage: The lamp's filament is designed to operate within a specific voltage range in order for it to deliver its intended light output. Lamps that are burned at voltages higher than their rating will result in higher wattage, efficacy (lumens per watt) and lumens. Lamps operated below their rated voltage will significantly increase their life while reducing their wattage, efficacy and lumen output.

Lumen Maintenance: As the filament of an incandescent lamp burns, the tungsten is slowly evaporating and depositing itself on the interior wall of the bulb. This creates the black coating seen after a bulb has been in use for a while. Additionally, as the filament evaporates, the lumen output decreases until it reaches the end of its life when the wire breaks. It is recommended that a "group replacement" or relamping is conducted once a number of lamps have failed or a noticeable decrease in light output has taken place.

Burning Position: For the most part, incandescent lamps can be burned in any position. However, take note and observe a lamp manufacturer's recommendations for use.

THE LIGHT BULB BASE

Screw-type bases used on incandescent lamps consist of three components: the threaded screw section, the glass insulation ring and the contact disc. The lead wires which exit the glass bulb of the lamp are attached to the base at two points. One wire is soldered to the bottom of the contact disc and the other to the top edge of the screw section. The glass ring acts as an insulation barrier between the two points. This assembly completes the circuit and the lamp is electrified once the base is screwed into a socket and the contact disc touches the center point of the socket.

The base itself has nothing to do with the seal of the bulb; it is a separate part of the lamp that is attached with cement. Typically, bases are made from aluminum or brass. Brass bases tend to perform best due to their compatibility with most socket materials.

TYPICAL LIGHT BULB SHAPES

The size and shape of a lamp's bulb are designated by a letter(s) and a number. The letter specifies the shape of the bulb and the number indicates the maximum diameter in 1/8-inch increments. Example: A G40 is a globe shape which is 5 inches in diameter.