Which rays are primarily used in ray treatments to increase pigmentation?

The choice highlighting UV-A and UV-B rays is accurate because these ultraviolet rays significantly influence the pigmentation process in the skin.

UV-A rays penetrate deeply into the skin and are responsible for the tanning effect, as they stimulate the production of melanin in the melanocytes, the cells responsible for skin pigmentation. UV-B rays, while primarily associated with sunburn, also play a crucial role in increasing melanin production, particularly in response to sun exposure. Together, these rays effectively enhance pigmentation by prompting the skin's natural defense mechanisms against UV radiation.

In contrast, the other options involve types of radiation that do not contribute to pigmentation in the same way. Infrared light is mainly associated with heat rather than skin pigmentation, and while UV-C can have harmful effects, it does not contribute positively to tanning or pigmentation. X-rays and Gamma rays, known for their penetrating power and potential harmful effects, are not used for pigmentation improvements. Finally, visible light and radio waves do not affect the skin's melanin production directly, making them ineffective for increasing pigmentation. Thus, the correct choice reflects the understanding of how specific UV rays interact with skin physiology to promote tanning and pigmentation.