incoherent light is light whose waves are not in phaseyou can compare incoherent light to rainfall; irregular wave pattern & choppy.one example of incoherent light is white light, however due to light waves' high frequency, white light looks even.

coherent light is light made up of waves of the same wavelength that are in phase with each othercoherent light can be created by a single point source. it has a regular wave pattern
A regular wavefront also can be created by multiple point sources when all point sources are in phase.

Between 1801 and 1803, English physician Thomas Young conducted investigations that confirmed the wave nature of light. In a key experiment, he passed light through a narrow slit to make it coherent, then through two closely spaced slits. The overlapping light produced a pattern of bright and dark bands on a screen, known as interference fringes. These resulted from constructive and destructive interference of light waves from the two slits.

When monochromatic light, which is light of only one wavelength, is used in a double slit investigation, the constructive interference produces a central bright band of that color with other bright bands of similar width and brightness on either side. the intensity of the bright bands decreases the farther the band is from the central band.between the bright bands there are dark bands which are the result of destructive interferencethe positions where constructive and destructive interference occur depends on the wavelength of that given color.

When white light is used in a double-slit investigation, however, interference causes the appearance of colored spectraThe various bands of color from the visible spectrum overlap on the screen.
All these colors have constructive interference, and the central band is white.
Because the positions of the other bright bands of constructive interference depend on wavelength, each color's band is at a different position, resulting in spectra of color.