eec247 Information on incandescent filament lighting

INCANDESCENT FILAMENT LIGHTING

Most people are under the mistaken belief that the "Light Bulb" was invented by Thomas Edison in 1879,
whereas it was invented a year earlier by Joseph Swan .

Since the end of 2011 this type of electric light is no longer available in the UK.
For domestic (and most commercial) applications, they have been replaced by Halogen , Compact Fluorescent and LED lighting.

We have included details of incandescent lighting here for completeness and comparison to other forms of lighting.
It's also of interest to us because it led to the accidental invention of "Electronics" .

The basic principle of incandescent filament lighting is fairly simple.
Take a piece of wire (or cotton soaked in carbon in Joseph Swan's original invention) - the filament.
Build the filament into a glass container (the bulb) with the ends accessible to make electrical contact later.
Pump out as much of the air as possible to stop the filament catching fire.
Apply a source of electricity between the two ends of the filament.
The filament gets hot enough to glow, but cannot burn as there is not enough oxygen in the closed bulb.

The "light bulb" is just the glass part of the lamp.
Lamp = "light bulb" + "filament" in a near vacuum.

Or in the words of a famous Electrician - "a bulb is something you stick in the ground and it grows into a flower".

A typical incandescent filament lamp in operation.

Early incandescent lamps with carbon filaments had a tenancy to deposit "soot"
on the inside of the glass bulb, making the lamp less efficient at generating light as it aged.
John Ambrose Fleming added a metal plate, not electrically connected to the filament inside the glass bulb
in an attempt to collect this "soot" and prolong the life of the lamp.
The initial results were not as good as expected, so in an attempt to attract the "soot" by
applying an electrostatic charge to it, he connected a battery between the plate and the filament.
If the battery was connected positive terminal to the plate and negative to the filament, current flowed in the circuit,
but if battery was connected negative terminal to the plate and positive to the filament, no current flowed.

John Ambrose Fleming had accidentally invented the "Thermionic Valve" (Diode) - the first ever electronic component.
Later he added an extra wire mesh between the filament and plate - the "control grid" to make the first "triode",
a valve capable of amplifying electrical signals.

Lee De Forest claimed to have invented the "triode" and spent years in court challenging Fleming's claim on the invention
until De Forest was finally credited with inventing the "triode".

Here is a magazine article from 1930 on "How Electric Lamps are Made".

How Electric Lamps are Made - from the Meccano Magazine 1930