Which type of radiation is commonly utilized in cosmetic tanning devices?

The correct choice is UV-A radiation. This type of radiation is commonly used in cosmetic tanning devices primarily because it has a longer wavelength, which allows it to penetrate the skin more deeply. UV-A rays are responsible for the tanning effect, as they stimulate melanocytes in the skin to produce melanin, the pigment that gives the skin its color.

While infrared radiation is primarily associated with heating effects and does not directly cause tanning, and X-ray radiation is used in medical imaging and does not contribute to tanning effects, the tanning process specifically relies on the action of UV-A and UV-B rays. In the context of cosmetic tanning, UV-B is also known to contribute to the tanning process but is less commonly utilized in tanning devices compared to UV-A due to its association with skin damage and increased risk of skin cancer.

Radio waves, on the other hand, do not have a tangible effect on skin pigmentation and are unrelated to the tanning process. Therefore, UV-A stands out as the appropriate choice for tanning devices in the cosmetic industry.