Wavelength is a measure of color just as pitch the wavelength of sound. These are harmful rays that may cause skin cancer. Used in the hospital to take pictures of the bones for possible fractures. Astronomers make extensive use of radiations in these two ranges to study the heavens. Lenses and mirrors are used for building telescopes.
Light is transmitted through transparent medium such as glass.
Light bends if it passes from one medium to another, and is called refraction of light. Ordinary Telescopes and Microscopes are built with two lenses, Objective lens and the eye-piece lens. This enables the image to be much magnified. A short plane mirror or converging secondary mirror is used to reflect the light back down the telescope tube through a hole at the center of the objective mirror. This arrangement is called Cassegrain telescope.