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Types of Light
To understand light you have to know that what we call light is only a specific type of light called visible light. Visible light is the light that humans can see. Other animals see different types of light. Dogs can see only shades of grey and some insects can see light from the ultraviolet part of the spectrum. The key thing to remember is that our light is what scientists call visible light.
Scientists also call light electromagnetic radiation. Visible light is only one small type of electromagnetic (EM) radiation. The entire spectrum measures the wavelengths of different types of radiation. Some radiation, such as radio waves, has very long wavelengths. Visible light is near the middle of the spectrum. Gamma rays and cosmic rays are at the other end of the spectrum and have very small wavelengths.
It's all Energy
The key thing to remember is that light and EM radiation are energy. There are very small particles moving in a wave pattern; it's just that simple. Scientists call those small particles photons, the wavelength determines the type of EM radiation, and the number of particles tells you how much radiation there is. A lot of photons give a brighter, more intense type of light. Fewer photons give a very dim and less intense light. When you use the dimmer switch on the wall, you are decreasing the number of photons sent from the light bulb. The type of light is the same while the amount has changed.
Different Speeds of Light?
As far as we know, all types of light move at one speed when in a vacuum. The speed of light in a vacuum is 299,792,458 meters per second. That speed is really fast but even when you're traveling that fast, it takes a while to get places in space. It takes about seven minutes for light from the Sun to reach Earth. It takes over four years for the light from our Sun to get to the nearest star. It would take a particle of light over 100,000 years to get from one side of our galaxy to the other side. All of those values are light moving through a vacuum. You can slow light down in other substances such as the atmosphere, water, or a diamond. Light moves at about 124,000,000 meters per second (less than half the speed in a vacuum) in a diamond. That changing speed is called refraction.
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