Led emits visible light when its

If infrared light is not visible to the human eye, why do most tv remote controls and security cameras appear to have a visible red colored LED lit when the infrared light is being emitted? Is that visible red light present as a convenience (introduced by grace of the component designer?) or as a by-product of emitting actual infrared light? Is it possible to have infrared light emitted without this visible red color? \$\begingroup\$ TV remotes do not typically have a visible LED in the front edge position that is aimed at the TV!!! They have it on the button panel (nowadays often under the translucent, soft buttons themselves), as a feedback that the remote control has battery power (it is working). \$\endgroup\$ The simple answer is that they are using near IR. LED manufacturers have a good handle on how to make them so they are affordable. Their center frequencies may be invisible to the M-1 eyeball ( i.e. human eye), but unless they put a filter in front of the LEDs (which cause them to produce less illumination) there will be some of it that you can see. The effect is minor. Basically, to see it you must look directly at the emitter. You're not going to see it in reflections or scene illumination. Far-IR is completely invisible. But a whole lot more expensive because the manufacturing process is different. Near-IR emitters are mass-produced. Far-IR not so much. IR lasers are another story. They emit on a single frequency, so there is no gaussian curve describing their...

The past few decades have brought a continuing and rapidly evolving sequence of technological revolutions, particularly in the digital arena, which has dramatically changed many aspects of our daily lives. The developing race among manufacturers of light emitting diodes ( LEDs) promises to produce, literally, the most visible and far-reaching transition to date. Recent advances in the design and manufacture of these miniature semiconductor devices may result in the obsolescence of the common light bulb, perhaps the most ubiquitous device utilized by modern society. The incandescent lamp is the best known of Thomas Edison's major inventions, and the only one to have persisted in use (and in nearly its original form) to the present day, now more than a century after its introduction. The phonograph, tickertape, and mimeograph machines have been replaced by digital technologies in the last few decades, and recently, full-spectrum light emitting diode devices are becoming widespread, and could force incandescent and fluorescent lamps into extinction. While some applications of LED technology may be as straightforward as replacing one light bulb with another, far more visionary changes may involve dramatic new mechanisms for utilizing light. As a result of the predicted evolution, walls, ceilings, or even entire buildings could become the targets for specialized lighting scenarios, and interior design changes might be accomplished through illumination effects rather than by rep...

Electromagnetic radiation is one of the many ways that energy travels through space. The heat from a burning fire, the light from the sun, the X-rays used by your doctor, as well as the energy used to cook food in a microwave are all forms of electromagnetic radiation. While these forms of energy might seem quite different from one another, they are related in that they all exhibit wavelike properties. If you’ve ever gone swimming in the ocean, you are already familiar with waves. Waves are simply disturbances in a particular physical medium or a field, resulting in a vibration or oscillation. The swell of a wave in the ocean, and the subsequent dip that follows, is simply a vibration or oscillation of the water at the ocean’s surface. Electromagnetic waves are similar, but they are also distinct in that they actually consist of 2 2 2 2 waves oscillating perpendicular to one another. One of the waves is an oscillating magnetic field; the other is an oscillating electric field. This can be visualized as follows: While it’s good to have a basic understanding of what electromagnetic radiation is, most chemists are less interested in the physics behind this type of energy, and are far more interested in how these waves interact with matter. More specifically, chemists study how different forms of electromagnetic radiation interact with atoms and molecules. From these interactions, a chemist can get information about a molecule’s structure, as well as the types of chemical bond...

The correct answer is option 4. Light Emitting Diode (LED) • It is a PN junction diode that emits light when it is forward-biased. • When forward current is passed through the light-emitting diode, carriers (electrons and holes) move. • The holes in the p-type region move to the n-type region and the electrons in the n-type region move to the p-type region. • The injected carriers recombine, and the energy difference before and after recombination is released as light. • The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor. • A light-emitting diode ( LED) is a semiconductor light source that emits light when current flows through it. • The forward voltage of an LED, V F, is the voltage that must be applied across the leads of the LED, from anode to cathode, in order for the LED to turn on. • Typically, the forward voltage of an LED is between 1.8 and 3.3 volts. • It varies by the color of the LED. • A red LED typically drops around 1.7 to 2.0 volts. • Since both voltage drop and light frequency increase with band-gap. • A blue LED drops around 3 to 3.3 volts. The correct option is 3 Concept: • Infrared radiation (IR), sometimes referred to simply as infrared, have wavelengths ranging from about 700 (nm) to 1 millimeter (mm). • They have wavelengths longer than those of visible light, but shorter than those of radio waves. • The frequencies of IR are higher than those of microwaves, but lower than those of visi...

The light emitting diode is the most visible type of semiconductor diode. They emit a fairly narrow bandwidth of either visible light at different coloured wavelengths, invisible infra-red light for remote controls or laser type light when a forward current is passed through them. The “ Light Emitting Diode” or LED as it is more commonly called, is basically just a specialised type of diode as they have very similar electrical characteristics to a PN junction diode. This means that an LED will pass current in its forward direction but block the flow of current in the reverse direction. Light emitting diodes are made from a very thin layer of fairly heavily doped semiconductor material and depending on the semiconductor material used and the amount of doping, when forward biased an LED will emit a coloured light at a particular spectral wavelength. When the diode is forward biased, electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable number of these photons can leave the junction and radiate away producing a coloured light output. LED Construction Then we can say that when operated in a forward biased direction Light Emitting Diodes are semiconductor devices that convert electrical energy into light energy. The construction of a Light Emitting Diode is very different from that of a normal signal d...

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