Visible crew/equipment: When Chloe shuts the door on Dan, a stage light is reflected in the glass of the door. (00:04:10)
Sweet Kicks - S1-E5
Visible crew/equipment: When sitting down in The Paddock Bar, the man next to Lucifer is wearing glasses that reflect a light screen. (00:12:30)
Favorite Son - S1-E6
Visible crew/equipment: When Linda and Lucifer are having a discussion at the end, a light screen is reflected in Linda's glasses. (00:39:10)
Visible crew/equipment: After the brief discussion in the hallway outside Linda's office, as Lucifer walks off a green screen is reflected in her glasses. (00:11:50)
Visible crew/equipment: When Lucifer jokingly says to Ricky that there's "nowhere to go but up", part of the crew/equipment is reflected in Ricky's glasses. (00:15:00)
A Priest Walks Into a Bar - S1-E9
Visible crew/equipment: When Linda is talking to Lucifer a white screen is reflected in her glasses. This can't be the window as the window is behind her. (00:03:30)
Answer: It's Lucifer's blood from when his wings got hit by the bullets. As Lucifer spreads his wings, they're white, and before he wraps them around Chloe, you see a bullet hit his wing above his right shoulder, and the spot turns red. After that, he continues to get shot in the wings before fleeing.
Bishop73
Agreed. His wings take damage and "bleed" similar to how he bleeds when Decker is around.
Ssiscool ★
If they were normal bird's wings, the lower part where there are just feathers should neither bleed like that nor be able to stop bullets, but they are angel's wings, so they behave differently.