Anytime you pull up behind another officer black your lights out. When you have your lights on it creates a silhouette effect. From the perp’s point of view, you have just outlined your partner and they can see exactly where they are standing and what they are doing.
On traffic stops, as you arrive as backup, turn the headlights down to the parking lights and only use your rear flash on your light bar.
This applies to any kind of call as well as traffic stops. Keep this in mind anytime you are a secondary unit responding.