How do Light Emitting Diodes Work?

Incandescent refers to a physical process by which any substance can be made to emit light when it is heated. A standard incandescent bulb has two contact points that connect the bulb to the circuit. The contact points are connected to the filament, which is securely held in place by a glass mount. The filament is made of a metal such as Tungsten, which has a melting point of 3,422°C.

The bulb itself is filled with an unreactive gas such as argon or xenon, which prevents the tungsten from melting. When the circuit is completed, the electrical current flows through the contacts and through the filament. The current itself is caused by the movement of electrons from a negatively charged region to a positive region. Electrons are sub atomic particles with a negative charge and will move toward a more positive region because there is a deficit of electrons.

When the electrons travel through the filament they impact upon the atoms of which it is made. These impacts cause the solid atoms to vibrate, which as any GCSE physics textbook will tell you causes them to heat up. A standard 60W bulb has a filament has a thickness of about 0.25mm. This is important because the thinner he filament the more rapidly it heats. Furthermore, the coil of tungsten is less than 3cm long, but is over 2 metres in length. The electrons can be made to travel at speeds close to that of light (300,000 metres / per second). It is this motion that causes the filament to light up and so the faster the electrons can be made to travel the brighter the bulb.

LED bulbs are different!

An additional term for LED lighting is solid state lighting (SSL) and brings forward a fundamental difference as compared to incandescent bulbs. In short the light is emitted direct from a piece of solid matter and not through a vacuum or unreactive gas.  In general terms, the solid state light emitting structure is made of a semi-conducting material. A diode is physical sciences term to describe the simplest type of semiconducting material.

As the name suggests, this is a substance that has variability in its electrical conducting properties. In an LED an alloy such as aluminium-gallium-arsenide is not in itself the conducting material. It has no electrons available to carry the current and so in its pure form is an insulator. To make the alloy more electrically conductive impurities are added. These added atoms create either a surplus of electrons or a space through which they can flow. The result is a substance that has positively and negatively charged layers as its structure.

The positive layer has space at the atomic level for electrons to travel through it and the negative layer has a surplus of electrons. When the circuit is complete the electrons are pushed through the positive space from the negatively charged layer. In other words the light is emitted when the electrons travel through the spaces.

The basic principle of transfer of electrical is the same no matter the type of bulb or appliance used. However, because of their very different components LED bulbs are superseding both Halogen and incandescent bulbs




Write a Comment