Light is one of the most fundamental aspects of the universe. It is the emission of electromagnetic radiation across varying wavelengths and frequencies. Light allows us to see and gives us information about the universe as a whole: the ages of stars, life cycles of stars and the temperature of celestial objects. Light can also tell us the relative densities of mediums. Light functions due to three fundamental properties.
The speed of light, which is 300,000 kilometers per second, is held to be the absolute upper speed limit of anything in the universe and the most fundamental property of light. Light travels at this velocity in absolute vacuum; traveling through another medium such as air or water slows light down. The speed of light is also crucial to the conversion between mass and energy: E=mc^2, where E is the energy measurement in joules, m is the mass in kilograms and c^2 is the speed of light squared. Therefore, a complete conversion of all mass to energy of a 10-kilogram object would be equal to 90 megajoules, or 90 million joules.
Light particles, or photons, reflect off other particles or masses and continue to travel at the same speed. Reflection allows us to see what we perceive as light reflecting off of objects into our eyes; the image scans onto the retina and passes to the occipital lobe of the brain and converts to electrical impulses. There are two types of reflection: specular reflection and diffuse reflection. In specular reflection, as from a mirror-like surface, the angle of incident--which is the angle at which light originally strikes the surface--will match the angle of reflection along the same plane. According to the Physics Classroom website, diffuse reflection from non-mirrorlike objects sends light rays in all directions because the molecular arrangement is irregular.
Color refers to the range of visible light on the electromagnetic spectrum, starting with red at the longest visible wavelength, then moving to orange, yellow, green, blue and finally violet at the shortest visible wavelength. When we see a color, we're seeing the reflection of only that wavelength. Color is also caused by white light splitting into its constituent colors when passed through a prism or other type of medium. When light passes through a prism and splits into several colors, the color we see depends on the angle of incident from which we see the light.