LED and Laser diode - class-XII

Given : $d = 9.6$ $\mu m = 9.6 \times 10^{-6}$ $m$      $D = 4.00$  $m$       $y _1 = 23$ cm $ = 0.23$ m

The color of an LED is a function of the material used to make the junction. There are two main flavors used in visible light LED junctions:

The colour of LED depends on the band gap of the semiconductor material used. When there is an electron transition, the light corresponding to that energy is emitted.

Theodore Harold maiman was the first to produce laser in $1960$.

In a He-Ne laser, metastable states are essential for the lasing action and exist in both Helium and Neon atoms. Helium is excited by electric discharge to a metastable state, then transfers energy to Neon atoms through collision, populating Neon's metastable state which leads to stimulated emission at 632.8 nm.

Due to non ideality in monochromatic nature of a laser, there exists some spread $\theta$, 

Laser action involves all of the following.
(i) Amplification of particular frequency.
(ii) Population of inversion.
(iii) Stimulated emission.

Wavelength of a laser beam can be used as a standard of  length because wavelength is considered as the measure of length of the wave.

A bulb is cannot be used in place of LED to detect weak currents because at weak current supply bulb cannot glow. Bulb requires specific minimum current to glow. but LED can glow at weak currents at low intensity hence Led is uesd to detect weak currents.

Principle of LED is the reverse of principle of photo electric effect.

LEDs are better than conventional incandescent power lamps because:-

A laser device produces amplification in the Ultraviolet or visible region of the spectrum. 

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation".