What is the difference between a laser light and an incandescent light?

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An incandescent light is a more technical term for traditional light bulbs, which produce light via incandescence. This is the term for the light emitted by objects when they're heated, in the same way that some metals will glow when placed in a fire. Incandescent lights use a piece of wire, usually tungsten, and transmit electrical energy into the wire, heating it until it's hot enough to glow. Note that not all light bulbs are incandescent; in many places they're being replaced with various other types of bulbs, such as fluorescent lights, due to the poor efficiency and lifetime of incandescent bulbs.

The main point of comparison between an incandescent and laser light is in the characteristics of the light they emit. Emitted light is typically the result of electrons in an atom absorbing and releasing specific wavelengths of light. Tungsten is a relatively heavy element with many electrons, thereby providing many different energies that the atom can absorb and release. This is part of why the light they emit appears white; it is releasing many different colors at once, but if you looked at the tungsten spectrum you'd see many differently-colored lines, each of which corresponds to the energy released from a specific electron transition. 

Laser light, by contrast, is defined as light that is emitted as a single wavelength, and all of those wavelengths are being emitted in phase, and in the same direction. This produces a light that has a single color and a very tightly focused beam. In comparison to incandescent light, this would be like taking just one of those electron transitions from tungsten, and only allowing that particular electron transition to take place, and then filtering it. In fact, this is basically what a laser does; by only allowing specific energies to excite its "medium" (i.e. whatever the laser is using instead of a tungsten wire) it only allows certain wavelengths of light to be generated; it then filters the wavelengths so that only the ones in phase are emitted, and it does this through a very narrow lens that produces a tightly-focused beam. 

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