Final answer:
The longest ultraviolet rays used in tanning booths are the UVA rays, which are considered longer in wavelength and 'safer' compared to UVB and UVC rays, yet they still present risks of cell damage and cancer with prolonged exposure.
Step-by-step explanation:
The ultraviolet rays that are the longest and most frequently used in tanning booths are UVA rays (A). The solar UV radiation is divided into three categories: UV-A, UV-B, and UV-C. UV-A rays have the longest wavelengths ranging from 320 to 400 nm and they make up 99% of the solar UV radiation that reaches the Earth’s surface. Most UV-B and all UV-C are absorbed by the ozone layer. Tanning salons use UV-A because of these longer wavelengths, which are also claimed to be "safe" UV, that have enough photon energy to activate the tanning process. However, it is important to understand that prolonged exposure to UV-A can still cause cell damage and potentially induce cancer.