VI Charactericstics of Optical LED SFH 756

VI Charactericstics of Optical LED SFH 756

Tags: Theory of Optical LED, LED: Principle action, Procedure for VI Characteristics of fiber optical LED, sample Tabular column of fiber optical LED, Model Graph of VI characteristic of Optical LED , VI characteristic of Optical LED,
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VI Characteristics of Optical LED


To study VI Characteristics of fiber optical LED

Apparatus Required

  • Fiber Optics Light Emitting Diode Module - 01
  • Plastic Fiber cable 1 meter - 01
  • Multimeter - 01
  • Adapter +12V/ DC - 02
  • Patch Chords - 04


LED: Principle action

A light-emitting diode (LED) is a semiconductor diode made by creation of a junction of n-type and p-type materials. Thus, the principle of an LED’s action works precisely the same way that we described the creation of permanent light radiation: the forward-biasing voltage, V, causes electrons and holes to enter the depletion region and recombine Figure 2. Alternatively, we can say that the external energy provided by V excites electrons at the conduction band. From there, they fall to the valence band and recombine with holes. Whatever point of view you prefer, the net result is light radiation by a semiconductor diode.

This concept is displayed by the circuit of an LED Figure 3. The difference is that in a regular diode these recombination release energy in the thermal—rather than the visible—portion of the spectrum. This is why these electronic devices are always warm when you turn them on. In an LED, however, these recombination results in the release of radiation in the visible, light, part of the spectrum. We call the first type of recombination non radiative, while the second type is called radiative recombination. In reality, both types of recombination occur in a diode, when a majority of recombinations are radiative, we have an LED.

Light Radiation by the PN junction of a Semiconductor


Fig1.Depletion Region and depletion voltage, VD


Fig2. Light Radiation has the result of electron pole recombinations

The forward current injects electrons into the depletion region, where they recombine with holes in radiative and nonradiative ways. Thus, nonradiative recombinations take excited electrons from useful, radiative recombination have and decrease the efficiency of the process. We characterize this by the internal quantum efficiency, ηint, which shows what fraction of the total number of excited (injected) electrons produces photons.


  • Connect +12V adapter on LED module.
  • Measure the series resistance R.
  • Switch (sw1) ON LED Module and Multimeter.
  • Connect the multimeter probe, positive to P1 and negative to P2 Ground.
  • Now we get a DC voltage output on multimeter and vary the pot meter min to max range (0V to 5V).
  • Connect P1 and P6 test point, P2 and P7 test point using patch chord.
  • Keep pot meter at minimum position.
  • Now vary the pot meter min to max and note down the reading of Resistor across voltage (Vr) and Diode across voltage (Vd).
  • Tabulate all the readings in below tabular column.
  • And plate voltage vs current curve.

Tabular column

Series Resistance R = 100Ω



Resistor across Voltage

          (Vr) in V

Diode across Voltage

           (Vd) in V

Diode current

(Id=Vr/R) in mA





Model Graph


Thus, the VI characteristic of Optical LED was plotted.

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