How Long After a V-Beam Treatment Can I Start Getting a Tan?

First off, your going to have a hard time getting a Dermatologist to OK a tan! A tan is a sign of injury to your skin. The skin is trying to protect itself from further injury by increasing the amount of pigment (melanin).
A good question is why did you get the V-Beam treatment? We often use the V-Beam for facial telangiectasia (veins), wrinkles, or brown spots (with the V-Beam Perfecta). These conditions are all precipitated and worsened by sun exposure. Good sun protection is key to obtaining and maintaining a good result.
I recommend strict sun precautions until all purpura (bruising) and redness from your treatment has faded. This would include an SPF of at least 30, hats and other physical protectants. Patients can then switch to an SPF of at least 15 daily -- but should still be using the above measures for anything more than routine daily sun exposure.

The sun thins the skin and creates more broken blood vessels.  While you can go into the sun after a period of time from your V-Beam, why would you want to with only an SPF 15 moisturizer? You should protect your skin with atleast an SPF 30 and stay out of the sun mid day.  Remember that a tan is a sign of damage to the skin and ultimately will make you need more V-Beam treatments.

The question you ask is similar to a lung patient asking her pulmonologist when he/she can smoke.  I would not recommend tanning other than the spray on type after V-Beam.  The sun's harmful rays will cause premature aging and skin cancer.