An electric light is a device that produces visible light from electric current. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and nighttime activities. In technical usage, a replaceable component that produces light from electricity is called a lamp. Lamps are commonly called light bulbs; for example, the incandescent light bulb. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the socket of a light fixture. The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap.
The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor.
- Incandescent light bulb, a heated filament inside a glass envelope
- LED lamp, a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light
- Arc lamp
- Xenon arc lamp
- Mercury-xenon arc lamp
- Ultra-high-performance lamp, an ultra-high-pressure mercury-vapor arc lamp for use in movie projectors
- Metal-halide lamp
- Gas-discharge lamp, a light source that generates light by sending an electric discharge through an ionized gas
- Fluorescent lamp
- Neon lamp
- Mercury-vapor lamp
- Sodium-vapor lamp
- Sulfur lamp
- Electrodeless lamp, a gas discharge lamp in which the power is transferred from outside the bulb to inside via electromagnetic fields
This is the supply voltage required for normal brightness. If a slightly higher voltage is used the lamp will be brighter but its lifetime will be shorter. With a lower supply voltage the lamp will be dimmer and its lifetime will be longer. The light from dim lamps has a yellow-orange colour.
Torch lamps pass a relatively large current and this significantly reduces the output voltage of the battery. Some voltage is used up inside the battery driving the large current through the small resistance of the battery itself (its ‘internal resistance’). As a result the correct voltage rating for a torch lamp is lower than the normal voltage of the battery which lights it!
For example: a lamp rated 3.5V 0.3A is correct for a 4.5V battery (three 1.5V cells) because when the lamp is connected the voltage across the battery falls to about 3.5V.
Source : Electronicsclub, Wikipedia
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