They should be used only according to the manufacturer's or a doctors instructions. These are not tanning lamps and too mush exposure can be harmful. Special goggles should be worn. Sunglasses aren't enough. The skin can be reddened and burned very quickly if you overdose.
If you have no medical need for UV skin treatment, don't use it.
If you want a tan, go to a sunny place and sit in the sun for 30 minutes. Even tanning lamps are discredited nowadays. I hope that when you turned it on you didn't stay in the same room without eye protection for more than a few seconds.