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Biasing of P-N Junction01:16

Biasing of P-N Junction

The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
In equilibrium, no external voltage is applied across the p-n junction. The depletion region is formed at the junction interface due to the diffusion of carriers, which leaves behind charged dopants, acceptors on the p-side, and donors on the n-side. These immobile charges create an electric field that prevents further diffusion of carriers. The related energy band...

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Related Experiment Video

Updated: May 12, 2026

Using Affordable LED Arrays for Photo-Stimulation of Neurons
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Published on: November 15, 2011

Far-field condition for light-emitting diode arrays.

Ivan Moreno1, Ching-Cherng Sun, Rumen Ivanov

  • 1Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Mexico. imoreno@fisica.uaz.edu.mx

Applied Optics
|April 10, 2013
PubMed
Summary

Researchers defined a far-zone condition for light propagation from LED arrays. The study found that highly directional LEDs significantly extend the near-zone, challenging the traditional rule of thumb for optical modeling.

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Area of Science:

  • Optics and Photonics
  • Solid-State Lighting
  • Electromagnetics

Background:

  • Light-emitting diodes (LEDs) are often modeled as point sources for optical propagation.
  • Traditional models assume a 'far-zone' condition based on source size, which may not apply to LED arrays.
  • Understanding the transition from near-field to far-field is crucial for accurate LED array design and measurement.

Purpose of the Study:

  • To establish a precise far-zone condition for light propagation from LED arrays.
  • To develop an equation for calculating the far-field distance based on array parameters.
  • To investigate the impact of LED directionality and packaging density on the far-field distance.

Main Methods:

  • Developing a theoretical model for light propagation from LED clusters.
  • Deriving an equation for far-field distance incorporating LED radiation patterns and array geometry.
  • Analyzing the influence of LED packaging density and beam directionality.
  • Simulating the effect of random light flux variations among LEDs.

Main Results:

  • A novel far-zone condition equation was proposed, dependent on LED radiation pattern, array geometry, and LED count.
  • Far-field distance is reduced in high packaging density arrays.
  • Highly directional LEDs significantly increase the far-field distance, extending the near zone beyond 60 times the array size.
  • Random variations in light flux have minimal impact on far-field variability in dense arrays.

Conclusions:

  • The classical '5 times source size' rule of thumb is insufficient for LED arrays, especially those with directional LEDs.
  • The derived far-zone condition provides a more accurate framework for modeling and measuring light propagation from LED arrays.
  • Array design parameters, particularly LED directionality and packaging density, critically influence the optical near-field and far-field characteristics.