What is the difference between a laser and flashlight?

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Answered by: Shamika, An Expert in the Light Category
A flashlight is an electric-powered light source; the light source is a light bulb or an LED. The electrical energy is converted into visible light. Flashlights can be hand-held or mounted to a platform. Light from a laser (light amplification by stimulated emission of radiation), on the other hand, is formed by exciting electrons to a higher state. When the electrons return to ground state and are hit by a photon, they emit photons, which have the same phase, frequency, polarization and direction of travel as the original photon.



This phenomenon is called stimulated emission. As these photons are reflected back and forth in the laser medium, their amplitude increases repeatedly. This results in a focused beam that is able to travel long distance without dispersing. The differences between a laser and flashlight lies in emission, coherence, phase, color and distance traveled.

Flashlight emits light by spontaneous emission. This means the emission is dependent on individual electrons. The electrons randomly emit photons to return to ground state. The electrons are not forced to emit a photon unlike in a laser. Lasers, however, produce light by stimulated emission. In this method, the electron is excited to a higher energy state, and the electrons return to ground state when perturbed by a photon. When returning to ground state, they emit a photon. Hence the emission of photons is stimulated.



In a flashlight, the photons aren't in phase with each other. As the emission of photons is unorganized, they can be in any phase. In a laser, the photons are in phase with each other. This is due to stimulated emission. The emitted photons are in phase with the stimulating photon. When these photons are represented graphically as a wave, they make the same angle at the origin. Hence they are said to be in phase with each other. If they do not make the same angle, they are said to be not in phase with each other. When all the photons in a beam of light are in phase with each other, the light is called to be coherent light. The light from a flashlight is called incoherent light.

The light from a flashlight cannot travel a long distance. This is because the light is unfocused and diverges as the traveled distance increases. The flashlight beam traveling distance depends on the size of the flashlight and the batteries being used. Laser light, however, can travel a long distance: Any laser light can be beamed to the moon and back. They can travel such long distances as they are coherent and do not spread out while traveling.

The final difference between a laser and flashlight is the color. Flashlights can display different colors. If flashlight beam is passed through a prism, it splits into the seven constituent colors of visible light. Lasers are monochromatic, meaning they can display only one color. This color depends on the laser medium. Lasers can have colors such as red, pink, violet, blue and also white. Whatever be the color, it cannot be split into other colors.

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