The most familiar is "reflection," in which light is bounced from a surface, the light coming off at the same angle at which it hits, resulting in your undistorted face looking back at you from a mirror. When it passes into a substance, it slows and can be bent, a common phenomenon called "refraction." The effect is easily seen when looking at something through water.
Refraction by a curved lens focuses radiation to create an image.
Ultraviolet runs from 4000 A down to about 100 A, X- rays take over to about 1 A, and these are followed by the gamma rays to no known lower limit.
Light and its partners can be manipulated in a variety of ways.
The violet limit therefore falls at 4000 A and the red limit near 7000 A or a bit longer.
Infrared runs from the red limit to about 0.1 millimeter, and the radio to as long as you wish, even to kilometers.
Turned to the sky and attached to a detector, the lens becomes an astronomical telescope.
(A curved mirror can create a similar image by reflection.) The speed of an electromagnetic wave in a medium depends on its wavelength.