Some Tanning beds can help treat Psoriasis however you need a Tanning Bed that produces both UVA and UVB light for the tanning bed to have an effect on the Psoriasis.
Most normal tanning beds do not put out the required type of light rays so you'll need to ask your tanning place whether there tanning beds provide UVA and UVB light sources otherwise they won't work for Psoriasis.