This is a commonly asked question especially since I practice in Florida. I usually recommend waiting as least 2 weeks following any vein treatment before getting sun burn over the areas treated. This is just a generality however. The longer one can avoid the sun post treatment the better. I also recommend a sun block of at least 30. The bottom line is that to avoid hyper pigmentation, one should use a sun block, avoid burning over the areas treated and wait for the treated areas to heal.
The main reason to avoid sun exposure after any vein treatments is to minimize the risk of hyperpigmentation which is a darkening of the skin over the closed vein. If the bruising is completely resolved and the skin overlying the vein appears normal, it should be ok to go in the sun. Use a sunscreen with at least an SPF of 50.