LED and other light sources

 

Lighting up the future

What is a LED?

LED stands for Lighting Emitting Diode although it is also known as SSL (Solid State Lighting or light emitted from a solid state). Technically it is a semiconductor diode that emits light when traversed by an electric current. The wavelength of light emitted (giving you the color you perceive) is only one (providing monochromatic light) and depend mainly on the chemical composition of the semiconductor material used.

Colour Diodes

 

But if the light provided by a LED is monochrome, how to get white light for indoor lighting when, in fact, white light comes only from colour mixing? There are two systems:

  1. Combining the light of three chips in different colours (blue, green and red) or
  2. Combining a chip that emits blue or ultraviolet light with phosphorus (the same technique applied on fluorescence).

The most common solution for interior lighting is the second, which is combining a blue LED with yellow phosphors (for cool white colour) or red and green phosphors (for the warm white).

LED lamps performance

Regardless of the brand or model, the principle of LED technology is the same: they operate with a relatively low voltage, 1 to 4 volts, the current is in a range between 10 and 40 milliamps (voltages and currents higher than indicated can melt a LED chip) and are formed in its central part for a semiconductor chip with two clearly differentiated regions: the areas dominated by positive charges p and n that is the negative.

 

In the absence of sufficient potential difference, the junction or joint acts as a barrier to the passage of electrons between regions. But when sufficient voltage is applied to the chip current can pass with the electrons cross the junction from the cathode to the anode.

 

When this current flows through the LED semiconductor chip, energy is released as photons with a light covering a range that goes from the ultraviolet to the near infrared.

 

Therefore, LED can be manufactured to provide any visible colour (except yellow range because there is no known semiconductor that generates a wavelength between 550 and 585 nm).

LED and other lamps

Edison discovered this way to generate light from electricity and its operation is based on circulating an electric current through a filament until it reaches a temperature high enough to get into incandescence and emit visible light. Average lasts is 1.000 h.

Halogen lamps are a type of incandescent lamp that last longer thanks to the incorporation of halogen gas compounds on the lamp's inside that allow a regeneration of the filament and, therefore, increased lamp life (2.000 to 4.000 hours).

Discharge lamps are an alternative way to produce light in a more efficient and economical than incandescent lamps. The luminescence is produced by excitation of a gas subjected to electrical discharges between two electrodes and, therefore, there are many types of discharge lamps (depending on the gas used and the working pressure) with different light characteristics. Discharge lamps can be classified as:

Low Presure Mercury Vapour Lamps:

  • Fluorescent lamps (from 2.000 to 10.000 h)

High Presure Mercury Vapour Lamps:

  • Mercury vapour lamps to high pressure (up to 16.000 h)
  • Mixing Light Lamps
  • Metal halide lamps (up to 9.000 h)

Sodium Vapour Lamps:

  • Sodium vapour lamps at low pressure (up to 14.000 h)
  • Sodium vapour lamps to high pressure (up to 16.000 h)

It is based on gas discharge at low pressure, but ignores the electrodes to cause the ionization and replaced by an induction coil without filaments and a coupling antenna (whose power comes from an external high-frequency generator) that create an electromagnetic field to induce electric current in the gas provoking its ionization. Its main advantage is the substantial increase lamp life (20.000 to 100.000 hours).

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