what exactly IS light?why does it spread?when a light source is turned on, why does the light spread? what causes the light itself to exert itself?light travels at 186000 mi/sec, but what exactly is it thats traveling?
Light, like all forms of electromagnetic radiation moves outward from its source in the form of wave packets. Think of dropping a stone in a perfectly still pool of water. As the stone hits the surface it produces ripples which move outward in concentric waves. Now, instead of the two dimensional water surface, light moves outward in concentric 360 degree spheres (waves) as long as the source generates them.
The real answer is rather complicated, but basically, light is made of of particles of energy. These particles are unlike the physical particles you are familiar with, in that they have no size, and do not have any mass or weight. These particles can sometimes behave remarkably like waves, and while we can predict what these particles can do with really immense and totally reliable precision, we do not have a sensible conceptual model for what light really is. That means, there is no simple picture or story or explanation one can give you. Light always moves at the speed of light. You ask why, and we can only say that that is the way light is. It is, you could say, the way we found the universe. When a light source is turned on, these particles of light - called photons are emitted by the electrons of the atoms and molecules in the filament or phosphors or LEDs or lasers. The photons then travel away at the speed of light. Because they have no mass, it takes them zero time to get to that speed. Really, this is a big subject, so I will end here. Perhaps other respondents will say more.
Light is an electromagnetic transverse wave composed of 2 oscillating fields, an electric field and a magnetic field travelling perpendicular to each other. EM radiation does not need any medium to travel through and as such can propagate through a vacuum. Light along with ALL EM waves travel at roughly 3x10^8m/s through a vacuum. If you want to know about what we consider visible light, well it is any EM radiation within a wavelength of about 410nm(Violet) - 700nm(Red). A nanometer is 10^-9m, very small indeed. Any radiation within that wavelength is visible light. That is actually the only difference between all types of EM radiation, their wavelengths, which in turn affects their frequencies and as a direct result of that affects their photon energy. How do we create light? light is generally created by electrons. Electrons exist in energy levels. From the lowest energy electrons (ground state) to higher energy levels. In an atom the electrons can become excited. They become excited when they ingest EM radiation. Electrons have to absorb an exact quanta of energy before they can jump to higher energy levels, this is further proof that energy is quantified. When an electron absorbs say UV light(which is of a very high frequency and thus energy) the electron jumps to the highest energy level. After a while the electron de-excites by jumping down energy levels, when it jumps down a level it emits a photon of EM radiation that is equal to the energy loss. The electron could jumps form say the 5th energy level, to the 4th, or from the 5th to the 3rd, or from the 5th to the 1st, it can jump from there to pretty much any energy level, the corresponding difference in the energy levels is what is emitted as a photon. Why does the light spread? well because light is always travelling, so once a source is turned on, light will travel in any and all directions.
Light is a wave of electric and magnetic fields traveling through space. it spreads because the source fires light in all directions, a laser beam stays focused because light is fired all in one direction. most light sources work as follows: electrons in the source matter (filament for example) are excited to higher orbits and given more energy either by heat or electric current, when an electron falls back and loses the energy it causes a tiny electric and magentic field ripple that travels in one direction, and that is light, many electronics ding the same thing and shooting ripples in every directions and we see the matter glow. the ilght wave is travelling at that speed. Did you know that it takes light 8 minutes to reach us from the sun? if the sun all of a suddon disappeared, we will only see that 8 minutes later...
