The Brief Answer: NO you cannot get a tan, but you can get a sunburn.
Mr. Wizard says: MH emits mentionable levels of UVB, HPS does not. Neither provides UVA. There is extensive discussion regarding adding UVB (a reptile light or the like) to your grow during flowering. Some (Ed Rosenthal, for one) say adding UVB will increase potency, I've never tried so I can't say.
How Tanning Happens
The sun's rays contain two types of ultraviolet radiation that reach your skin: UVA and UVB. UVB radiation burns the upper layers of skin (the epidermis), causing sunburns.
UVA radiation is what makes people tan. UVA rays penetrate to the lower layers of the epidermis, where they trigger cells called melanocytes (pronounced: mel-an-oh-sites) to produce melanin. Melanin is the brown pigment that causes tanning.
Melanin is the body's way of protecting skin from burning. Darker-skinned people tan more deeply than lighter-skinned people because their melanocytes produce more melanin. But just because a person doesn't burn does not mean that he or she is also protected against skin cancer and other problems