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How light bulbs work

Filament BulbTungsten Incandescent

Often termed the “Normal” bulb, now being phased-out due to its’ high energy requirements. By far the simplest of all bulbs, it passes an electric current through a tungsten filament (thin wire), the resistance of the wire causes it to heat up to the point where it glows brightly. Initially the glass bulbs held a vacuum to prevent oxidisation of the filament wire, but later an inert gas was used for safety, cost and improved filament lifespan (by absorbing heat from the filament).

The properties of the bulb are:

Halogen Incandescent

The halogen bulb is similar to a standard incandescent bulb, but instead of using an inert gas inside the bulb, it uses a halogen gas that gives the bulb some improved properties. A chemical process causes the evaporated tungsten to be re-deposited onto the filament improving lifespan and causing no “soot” to form on the inside of the glass bulb.

Halogen BulbsThe properties of the bulb are:

Fluorescent

Fluorescent lamps have been available as tube lights for many years however in the last decade they have also become common as light bulbs. The tubes are filled with a low-pressure mix of mercury and an inert gas. When a voltage is applied across the tube, electrons begin to travel though the low-pressure gas forming a plasma. In the plasma the electrons impart energy in to the mercury atoms, the mercury then releases the energy in the form of photons (light). Unfortunately the photons released by the mercury are ultraviolet (black light) and cannot be seen by the human eye. To solve this, the inside of the glass tube is coated in a phosphor powder which glows when the ultra violet light hits it.

The properties of the bulb are:

LED Filament BulbLED

The latest technology is the Light-emitting diode based bulbs, LEDs have also been around for a long time but only recently has the cost of LEDs (of sufficient brightness and colour) reduced enough to be competitive in the light bulb market. LEDs work in a way similar to the fluorescent tubes, by forcing energy into atoms then the atoms releasing the energy in the form of photons but there is no plasma with the LED method. LEDs are formed using semiconductors, where a junction is formed on a semiconductor by doping with impurities. Some impurities remove electrons from the semiconductor atoms and some create more electrons. In an LED, when a voltage is applied across the junction, electrons are continually absorbed into atoms that are missing electrons. As the electron is absorbed, energy in the form of photons is released. The colour of the light emitted depends on the impurities used to dope the semiconductor.

The properties of the LED bulb are:

Caveats

When it comes to lamps like CFL and LED, where electronics is used to modify the mains voltage to a compatible form (high-frequency for CFL and DC for LED), the electronics must be compatible with the trailing-edge dimmer.