Sirius Glass
Subscriber
We have a reliable flashing device on hand almost all the time today. A phone screen out of focus with a white (or coloured) frame.
Latensification is just about even illumination that is below reciprocity failure for build up of a significant image over a given time frame. I've used a door frame gab over 15 minutes in a bathroom successfully. Crude but effective.
Meanwhile the people and things have moved on and the photographic opportunity was lost.