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How light bulbs work!

How light bulbs work!. Construction Light bulbs have a simple structure. They have 2 metal contacts that connect to the end of a circuit These are attached to stiff wires which instead are attached to a thin metal filament. The wires & the

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How light bulbs work!

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  1. How light bulbs work! Construction Light bulbs have a simple structure. They have 2 metal contacts that connect to the end of a circuit These are attached to stiff wires which instead are attached to a thin metal filament. The wires & the filament are enclosed in a glass bulb filled with inert gas such as argon to prevent the filament from burning out. Working On connecting the bulb to a power supply, • Electric current flows from 1 contact to the other, through the wires & filaments. • As the electrons pass through the filament, they constantly bump into the atoms that make up the filament & this causes the atoms to vibrate. • In other words, heat is generated and this is converted to light energy.

  2. Light Emitting Diodes A Light emitting diode is a semiconductor device that emits Incoherent narrow-spectrum light when electrically biased in the forward direction. The color of the light depends on the chemical composition of the semiconductor material used, and can be near ultraviolet, visible or infrared. They are made up of materials characterized by a wider gap between the conduction band and the lower orbitals. The size of the gap depends on the frequency of the photon and hence plays a major role in determining the color of the light. LEDs are specially designed to release a large no. of photons outward. They are housed in a plastic bulb that concentrates the light in a particular direction. Most of the light bounces off the sides of the bulb, traveling on through the rounded end.

  3. THE BASIC LED White LED specifications Voltage: 3.6 VDc Current: 30 mA Power: 100 mW Construction Positive power is applied to 1 side of the LED semiconductor through a lead (anode) and a whisker. The Other terminal (cathode) is attached to the anvil. The entire unit is totally embedded in epoxy which makes the LED indestructible. The epoxy resin enclosure has 3 functions: • Designed to allow most light to escape from the semiconductor • It focuses the light i.e. view angle • Protects the assembly from outside elements Hence, it is essentially a PN junction semiconductor diode that emits light when current is applied.

  4. Working of Diodes In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free electrons (negatively-charged particles) to conduct electric current. In doped material, additional atoms change the balance, either adding free electrons or creating holes where electrons can go. Either of these additions make the material more conductive. At the junction of a p-type and an n-type semiconductor there forms a region called the depletion zone which blocks current conduction from the n-type region to the p-type region, but allows current to conduct from the p-type region to the n-type region. Thus when the device is forward biased, with the p-side at higher electric potential, the diode conducts current easily; but the current is very small when the diode is reverse biased.

  5. Principle The approach is based on the encapsulation of semiconductor quantum dots and engineering their surfaces so that they emit visible light when excited by UV light emitting diodes (LEDs) The Quantum dots strongly absorb light in the near UV range and re-emit visible light. The color of the light depends on the Size and Surface chemistry of the Quantum dots.

  6. Quantum dot LEDs • Similar but versatileQLEDs (Quantum Light Emitting Diodes) made out of networks of quantum dots would operate in a manner similar to a traditional LED, but with much greater versatility. • Current encounters discretized energy bands specific to Q. dotsElectrical current would still be driven through the quantum dot network, but instead of encountering traditional semiconductor energy bands, the current would encounter the discretized energy bands specific to quantum dots. The discretized nature of quantum dot bands means that the energy separation between the valence and conduction bands (the bandgap) can be altered with the addition or the subtraction of just one atom – making for a size dependent bandgap. • SizePredetermining the size of the QLED’s dots would fix the emitted photon wavelength at the appropriate specified color, even if it is not naturally occurring – an ability limited only to dots. In addition, the extremely small size and versatility of form for quantum dots allows them to be inserted into any medium necessary – paint, water, plastics and more. Size plays an important role in affecting material properties; electrical, nonlinear optical etc. If excited; smaller the dot  higher the energy & intensity of the emitted light.

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