Gyms should appear bright, airy and clean. People need to get motivated to exercise and what a better way to give them that motivation with the proper light.
Spas on the other hand, need to have a discreet relaxing lighting to create the perfect mood to clients and making the spa experience their favorite choice to relax and melt away stress.
Tanning salons use tanning beds which contain tube lamps, producing an Ultraviolet light which is responsible for an artificial skin tanning. Consequently, salons need to ensure the health safety on clients, since the skin is the largest organ in the body and is easily affected by light.
Fluorescent tanning lamps require an electrical ballast, specialized in UV, to limit the amount of current going through the lamp. While the resistance of an incandescent lamp filament inherently limits the current inside the lamp, tanning lamps do not and instead have negative resistance. They are plasma devices, like aneon sign, and will pass as much current as the external circuit will provide, even to the point of self-destruction. Thus a ballast is needed to regulate the current through them.