I saw a movie maybe the most recent time was in the early 90’s. The scene that I can recall is as follows.
An elderly couple come to visit family, I believe that it was already after the court proceedings were over. The proceedings were in regards to a murder that happened in the house they are at. I don’t recall if it was the husband who killed his wife & family or if the wife killed her husband. The elderly couple were the parents of one of them. When they came to give their support. They were told to take the Master Bedroom to sleep while they are there. So, they did. And that night when they were in bed talking to each other and once the lamp went off. They were shocked to see the room was not lluminated with the Luminal the police had used and it caused the room to be lit up like a Christmas tree because of all the blood that had been in the room and was detected by the luminal. And the elderly couple looked at each other in horror.