Electric Lamp | Types of Electric Lamp

An electric lamp is a replaceable or integrated light source used for illumination, signalling or indication. Electric lamps include several technologies. This page focuses on miniature incandescent lamps, in which a tungsten filament is enclosed in a glass bulb containing vacuum or inert gas. When current heats the filament to incandescence, it emits visible light. Tungsten’s high melting point permits a high operating temperature, but gradual evaporation still limits lamp life.

Uses of Electric Lamps

Miniature incandescent lamps have been used for panel lighting, indicators and instrument displays. In many new products, light emitting diodes provide longer life and lower energy use. Incandescent lamps still appear where their optical pattern, simple drive or compatibility with existing holders is useful, but LEDs now serve many former lamp applications.

Rating of Electric Lamps

Select a lamp by its electrical ratings, light output, service conditions and mechanical cap or lead arrangement. The following two electrical markings are common.

1. The rated Voltage of an electric lamp is the supply voltage for its specified performance and life. Operating an incandescent lamp below that value reduces filament temperature and light output. Excess voltage raises filament temperature sharply and can shorten life or cause immediate failure.
2. Power Rating or Current Rating of Electric Lamp:
   At rated voltage and normal operating temperature, filament current depends on hot electrical resistance. The cold resistance is much lower, so switch-on current can exceed steady current. Rated voltage and rated current determine rated power under the stated conditions.
   

   For a DC lamp or a resistive lamp at the specified RMS AC supply, electric power is P = VI. A manufacturer may mark voltage with watts, amperes or both. Selection must also match bulb temperature limits, holder rating and required light output.

   
   

Types of Electric Lamps

The types of an electric lamp shown below are miniature incandescent package and connection styles. Informal names such as MES or small bayonet do not by themselves guarantee interchangeability. Check the standard cap designation, voltage, dimensions, contact arrangement and holder drawing for the actual part.

Edison Screw type Lamps

An Edison screw lamp has one contact at the base tip and the other on the threaded metal shell. The thread mates with a holder of the same standard size. Two miniature names often encountered are:

1. Miniature Edison Screw Lamp (MES), commonly associated with an approximately 10 mm screw cap.
2. Lilliput Edison Screw Lamp (LES), commonly associated with an approximately 5 mm screw cap.

Miniature Center Contact type Lamps

A miniature centre-contact lamp has one base contact and uses the metal shell as the other connection, like a single-contact screw lamp. The shell has bayonet pins rather than a thread. The illustrated product is about 10 mm in diameter, but actual dimensions and pin geometry must match the holder specification.

Small Bayonet Cap Lamps

A double-contact bayonet cap carries both electrical contacts on its insulated base, so the metal shell need not form a circuit connection. Filament orientation and optical alignment depend on the application. The pictured lamp’s approximate 40 mm bulb and rating up to 24 W are example product characteristics, not limits for every small bayonet family.

Wire Ended Lamps

Wire-ended miniature lamps bring two leads directly through the glass seal instead of using a separate cap. Some products are only a few millimetres long and are intended for low-power indicators or backlighting. The leads can be soldered to a circuit board if the part data permits it, with care to limit heat and mechanical stress at the glass seal.