From American Cinematographer, Cinematography for Blade Runner by Herb A. Lightman and Richard Patterson (July 1982)
"After many tests with various units, gaffer Dick Hart came up with the most effective light to do the job, a Xenon spotlight commonly used for night advertising at sports events. This concept gave us some wonderful opportunities. For example, there's a late-night scene in Deckard's apartment kitchen which was played with the lights out. He has just had a hell of a struggle with one of the replicants. Having barely survived, he is now standing near the refrigerator. Rachel [Sean Young] is standing by the sink, which has a window above it. She is illuminated by a soft backlight through the window and the last traces of light filtering across the room from the refrigerator. Occasionally, one of those strong beams of light cuts through the sink window and glows the room just enough to read her face.
Naturally to create shafts of light, one must have some medium, which necessitated the use of smoke. The story lent itself very well to it, in the context of a highly polluted environment. It was very interesting to work with this constant atmosphere. Smoke is wonderul photographically, but not without its problems. It's hard to control, mainly due to drafts, and a lot of people find it objectionable to work in. Beyond this, it's important to keep the smoke level density constant, as a very subtle change in this density can result in dramatic changes in contrast. The only practical way to judge smoke density is by eye. [He jokingly adds,] I find that a good density is achieved just before I lose consciousness."
Cronenweth wanted to maintain the same texture even in situations where smoke wasn't used as heavily, and accomplished this by using low-contrast filters. He details, "We changed filters in conjunction with the angle of light and density of smoke. The stronger the backlight, the lighter the filter."
- Jordan Cronenweth, ASC