Two Light Fakes Among Six

You have 6 visually identical coins. Exactly TWO of them are counterfeit and each counterfeit weighs the same known-lighter amount (both fakes are equally light); the other four are genuine and equal. Using a two-pan balance scale (each weighing returns left-heavy, right-heavy, or balanced), what is the minimum number of weighings that guarantees identifying WHICH two coins are the light pair in the worst case? Weighings may be adaptive.