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two coherent light sources are produced by splitting a single light source
coherent light is a light in which the electromagnetic waves maintain a fixed and predictable phase relationship with each other over a period of time. Additional Information (S) Incoherent light contains may different wavelengths and amplitudes of light, such as light from a light bulb. Coherent light is a beam of light where all of the photons are the same frequency and interval. If you think of photons like people, a laser is a coherent group of photons like a column of soldiers marching in a long parade, whereas incoherent light is more like everyone exiting from the movie theater.
Coherent sources are sources of light with a constant phase difference. The conditions for this are that there is a constant phase difference and that the light is of the same wavelength.
Laser light is said to be coherent; regular light such as the type produced by an incandescent bulb is incoherent. In coherent light, all the wavelengths are the same, and all the directions are the same, everything lines up and is perfectly uniform. With incoherent light, you get a messy mixture of wavelengths and directions. Light from a laser is collimated - i.e. aligned such that all the light rays are oriented parallel to each other. For this reason, you do not see laser light unless some of it is deflected by striking a something in its path or you are looking directly at it. In a filament lamp, the light rays are oriented in nearly all directions.
Coherent waves in the electromagnetic spectrum are produced by masers, for microwaves, and lasers, for light.
First let us remove the word visible from this question and replace it with incoherent, as visible light can be either coherent or incoherent and coherent light can be either inside the visible spectrum or outside it.Incoherent light is random/unordered, e.g. wave phases different, shines in all directions, polychromatic.Coherent light is ordered in one or more ways, e.g. wave phases all synchronized, shines in one unidirectional collimated beam, monochromatic.The difference between light in the visible spectrum or outside it is only whether humans can see it or not, there is no difference in the light itself other than wavelength.
The photons (units of light) in incoherent light fly around like, say pepper and water in a blender. The photon in LASER light all move in the same direction like soldiers marching together down a street. LASER light is 'Coherent' light. This means that a beam of coherent light can travel great distances without spreading out.
LEDs, known as light emitting diodes, are comprised of two lead semiconductor light sources. Laser transmitters, also known as laser diodes are comprised of an electrically charged semiconductor laser.
i dont know but can we see without reflection?
No. Unless the LED is specifically a laser, you can not make it focus like a laser by putting it in a housing. A laser produces coherent light, which is why it acts like a beam. A normal LED is not coherent, and you can not make it so. Although you can not make a collimated incoherent light beam able to travel similar distances as a collimated laser beam, you can collimate incoherent light into a beam which would travel some distance with a small amount of divergence.
By splitting what is originally a single beam of light.
You have to correct the question as,Why are two independent sources of light not used to illuminate the two slits in Young's double slit experiment?We need coherent sources. But two independent sources would emit waves with varying phase difference which makes waves non coherent.