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Laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. Laser devices create a uniform and coherent light that is very different from an ordinary light bulb. Many lasers deliver light in an almost perfectly parallel beam (collimated) that is very close to a single wavelength which allows the Laser's light to be focused down to a tiny spot.
Class IIIa: This includes those lasers emitting ultraviolet or infrared light as well as visible light. All devices within the Class I AEL (Allowed Exposure Level) with laser output between .18μm and 1mm fall in this class. (Common Laser pointers are Class IIIa laser devices.)
Class IIIb: These include the same spectrum as Class IIIa, but increase the output levels to that of Class II AEL.
Class IV Lasers: This class of lasers includes any that exceeds the Class II AEL. Almost every laser that produces an excess of 0.5 watts is in this class. Laser hair removal, photofacials, laser resurfacing are all Class IV lasers and are classified as medical devices that must be used or overseen by a physician.
Light is really an electromagnetic wave. Each wave has brightness and color and vibrates at a certain angle which is called polarization. This is also true for laser light but it is more parallel than any other light source. Every part of the beam travels the exact (almost) same direction causing the beam to diverge very little. With a good laser, an object at a distance of 1 km (0.6 mile) can be illuminated with a dot that is about 60 mm (2.3 inches) in radius.
Because it is so parallel, the laser can also be focused on very small diameters where the concentration of light energy becomes so great that it can be maneuvered and used it to cut or drill. It also makes it possible to illuminate and examine very tiny details. This property is used in surgical appliances and CD players.
It can also be made very monochromic, so that just one light wavelength is present. This is not the case with ordinary light sources. White light contains all the colors in the spectrum, but even a colored light, such as a red LED (Light Emitting Diode) contains continuous intervals of red wavelengths.
On the other hand, laser emissions are not usually very strong when it comes to energy content. A very powerful laser of that kind is used in laser shows and doesn't give off anymore light than an ordinary streetlight; the difference is how parallel it is.
Low level laser therapy (LLLT) is a light source treatment that generates light of a single wavelength. LLLT emits no heat, sound, or vibration. Instead of producing a thermal effect, LLLT may act via nonthermal or photochemical reactions in the cells, also referred to as photobiology or biostimulation.