Huygens noted that when light waves passed through an opening, they or diffract and then undergo interference to produce bands that are brighter and darker.

Refract

Explanation:

The Huygens-Fresnel principle states that every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.

The principle can be shown with the equation below: s=vt s – distance v – propagation speed t – time Each point on the wavefront emits a wave at speed, v. The emitted waves are semicircular, and occur at t, time later. The new wavefront is tangent to the wavelets.

When a beam of light travels between two media having different refractive indices, the beam undergoes refraction, and changes direction when it passes from the first medium into the second. To determine whether the light beam is composed of waves or particles, a model for each can be devised to explain the phenomenon.

According to Huygens' wave theory, a small portion of each angled wavefront should impact the second medium before the rest of the front reaches the interface. This portion will start to move through the second medium while the rest of the wave is still traveling in the first medium, but will move more slowly due to the higher refractive index of the second medium. Because the wavefront is now traveling at two different speeds, it will bend into the second medium, thus changing the angle of propagation. In contrast, particle theory has a rather difficult time explaining why particles of light should change direction when they pass from one medium into another.

think its the third option

wavelegth as in spectrum red oygbiv