In the Sherlock, Abominable Bride episode, a particular scene caught my attention. In the opening scene just when Mike Stamford and Dr. Watson are heading to meet Sherlock, in the backdrop we can see a man with curly ruffled hair searching through some books, in dim white light. The entire area is candle lit(Victorian era), so how come only this specific room has dim white light?
Also from that angle the person in the room seems to be the modern day Sherlock. Is this scene a deliberate attempt(clue) to show that it is all going on in Sherlock's head?