It is very difficult to make a comparison between indoor tanning and tanning in the natural sun. This is because there are so many variables that make up tanning. For example, at different times of the day the sun emits differing rations of UV rays, and intensity. There are other numerous factors that affect natural sun as well such as clouds, pollution, time of year, etc. In each piece of tanning equipment, lamps also emit varying ratios of UV rays. With all the factors to consider, there is no simple way to correlate the two types of tanning in terms of minutes or sessions.