Asking to a dermatologist about what type of tanning is safe to skin. His answer is there is none. No tanning bed is safe either except those spraying color onto skin.
The mechanism of tanning by light is UV light triggering protective reaction from skin. UV light, and any other type of radiation waves including X-ray, beta-Ray, ect, are the same in nature. They are all electromagnetic waves with different wave lengths which render them the different penetration powers. Such energy can cause molecular disturbance in DNA structure and cause mutation, which lead to destruction, aging and neoplasm including cancer in tissue. UV light has limited penetration powers and only causes damage to skin. The skin tries to protect itself by producing melanin which is tanning. However, such protective response is partial in its effectiveness. UV light to skin is like smoking to lung. The harmful effect is cumulative with time. Victim will not notice the damage until later in life.
A lot of young people choose to tan their skin. Some might choose with above knowledge in their head and it is matter of life choice. I suspect a lot of young people choose to tan so as result of ignorance
. Only they noticed the harm in early started in their 30s with aging winkled skins. Too late! Low IQ and ignorace might shorten people's life. Had they known earlier, they might have done thing differently. People with Knowledge certainly will live longer and healthier