Which one of the following LED emits an invisible light?

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SDSC (ISRO) Technician B (Electronic Mechanic): Previous Year Paper (Held on 29 April 2018)
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  1. Laser LED
  2. Bicolour LED
  3. Infra-red LED
  4. Tricolor LED

Answer (Detailed Solution Below)

Option 3 : Infra-red LED
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Detailed Solution

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INFRA-RED(IR) LED:

An IR LED (infrared light-emitting diode) is a solid-state lighting (SSL) device that emits light in the infrared range of the electromagnetic radiation spectrum.

F2 Shubham 19.1.21 Pallavi D 6

  • IR LEDs allow for cheap, efficient production of infrared light, which is electromagnetic radiation in the 700 nm to 1mm range.
  • IR LEDs are useful in electronics, which includes many types of remote controls for televisions and other electronics.
  • Used with infrared cameras, IR LEDs can act as a spotlight while remaining invisible to the naked eye.

 

LASER:

  • Laser, a device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation.
  •  The emission generally covers an extremely limited range of visible, infrared, or ultraviolet wavelengths.

 

BICOLOUR LED:

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A Bi-Color light by definition is one that can offer the user multiple color temperatures. 

For example A TRAFFIC SIGNAL,

  • When current is fed into the array in a first direction, the bicolor bipolar LEDs (16) display a first color, which may be green.
  • When current is fed into the array in a second direction, the bicolor bipolar LEDs (16) display a second color, which may be red.

 

TRICOLOUR LED:

A Tri-Color LED is an LED that can light up into two different colors depending on where the current flows to on the LED.

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  • In the 3 terminal tri-color LEDs, the LEDs have a common ground or cathode. A positive voltage applied to either of the other two wires is used to light the corresponding LED.
  • A tri-color LED is useful as an indicator.  For example, on a digital camera, a tri-color LED may glow red when it is in recording mode and green when it is in play mode.
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