Monochromatic Light: It consists only single wave of the spectrum of light. Monochromatic light is used in the spectrophotoscopy.
Polychromatic Light: It consists bundle of waves at the same time. Polychromatic light is used in the X-ray machines, Microwaves and so on.
Monochromatic Spectrophotoscopy: The spectrophotometer which allows only single wave out via the whole spectrum. It generates only single wave at one time.
It happens with the help of monochromator, the spectrophotometer passes the light through the monochromator, this monochromator allows the polychromatic light (bundle of waves) or spectrum, to pass on through the entrance slit of the monochromator and allows only one wave to come out through the slit.
Polychromatic Spectrophotoscopy: Polychromatic light is the bundle of waves which generates at the same time. Mostly in the spectrophotometer, monochromator is used to generate the single wave or monochromatic wave at a time by Polychromatic wave.