Why lasers and not light? Some laser applications consist simply concentrating light into a small spot (e.g., image projection, welding, cutting, etc.). Why are lasers used instead of a simpler light source?
 A: Lasers are coherent light sources, meaning that all of the light is of the same wavelength, relative phase, and direction. This is as opposed to other light sources which typically release a spectrum of wavelengths (producing white light) in all directions. Because all the light is of the same wavelength and relative phase, it is easier to work with the laser light and fine-tune it to whatever application you have. Also, lasers tend to be more energy efficient than other light sources. For example, if you wanted to create a really bright incandescent light to do welding with, such a source of light would also generate an immense amount of heat such that even if you could direct all of the light at one spot without significant losses, you'd run into other problems.
A: A traditional sphere-shaped lightbulb emits light in all directions, if you would use a lens to focus it, a great amount would be lost. The lightwaves laser emits are all parallel with each other, so I think you can focus it to one small spot a lot better than a lightsource where photons go in all directions.
