This is a technical response to an email I received.  Read this in place of a sleeping pill. 

QUESTION: 

Hello X.N.,
My son and I saw your work at the Des Moines art show.  We really liked your work and spoke with you for a while about the night shots you do.  We’ve been contemplating trying some shots of our own.  You said, and correct me if I’m wrong, that you use 100 or 200 speed film, and that you use 30 to 45 minute exposures.  And judging from the depth of field in your photos, I’m guessing that your aperture is as small as it can go.  (forgive my lack of photography lingo).  How much “filling in” do you do with the flash?  For instance, the picture on your website of “San Francisco ruins”….  how much of that had to be filled in with flash and how much is sodium and mercury vapor?  How many flashes per position?  What time of day was it (at what time of the year)?  Was there moonlight?   I hope you don’t mind an amatuer pestering you for tips, but I was fascinated by your work (note shameless flattery).  I also enjoy the photos on “lost america”… google that if you haven’t seen it before.    
One last question, could one use a faster film (400) / shorter exposure (10 min) and still get the same effects / quality.
Thanks for your time and thanks for coming to DM and inspiring us.  Hope to see you next year. 
JJ

RESPONSE:

I learned most of my techniques through trial and error - there is no formula that will explain the way every shot was done, as each image is a custom built photograph. The best way to learn this is just by going out shooting. Having said that, here’s some information you should find useful.
First, the film…
I use Kodak Ultra 100asa film. Its a film that gives me very rich colors. The 120mm film version was discontinued a year ago (but I have a 10-year supply of it in the freezer… bouahahahah!!). They may still have it in 35mm. The film I used before this was Agfa Ultra 50 asa 120mm. I used it from Alley 25 to Alley 57. I took a 4-year break (between #57 and #58) from shooting alleys for several reasons. When I returned, the Agfa had been discontinued and I wanted to cry because it was such an amazing film. It may still be available in 35mm, in which case I’d suggest you start with that. I then discovered Kodak Ultra (which also gives me great colors at night), so the heartache was short-lived, but I learned my lesson, which explains the freezer-full.
The lower the asa, the richer and more contrasty your colors will be (plus the image will be sharper and less grainy). If I shot with a 400asa film, a 60-minute shot would be reduced to 15-minutes, which is great, but the final result would be an inferior image, which is not so great.
Exposure time:
My exposures run from less than a minute (rare) to 90-minutes (rare). Most run in the 10-15-minute range. All the controls are customized for the specific shot, so although I want the aperture to be closed down to get everything in focus, sometimes it is almost wide-open. Stadium and Window Fire and others were almost wide open because the settings were extremely dark. Closing another stop for Stadium would have given me greater depth of field (which I wish I had), but would have meant a 3-hour exposure, instead of the 90-minutes I opted for. A side note: closing “all the way” can be detrimental to image quality. Optimal is roughly 80% closed down.
Lighting:
Once again every shot is unique. I’ve used everything from a small pen light to hi-lite a tiny area (the street poster gun in Can’t Sleep), to enough lighting to fill most of the frame (Green Door). And when I started the series in 1991 and for several years, I forbid myself from using any of my lighting (or even moving anything at all), under punishment of death.

         
Today I light most of my images. A recent example is Angel Luis. During this 10-minute exposure I walked/ran around with a 30CC Green Lee gel on my flash, pointing it down, firing it, and doing what’s called “light painting.” The 30CC replicates fluorescent lighting on daylight balanced film. I have a whole set of Lee gels (i.e. filters for lights) that I look through to decide on my lighting.  WAKE UP, WAKE UP! I’M NOT FINISHED!
I then switched gels to a 1/2 CTB (blue) Lee gel and continued my lighting, again firing it numerous times.

          
“Goast Pier,” my recent San Francisco pier shot is a case where I used a hi-powered halogen spot light to light the entire building, a quarter of a mile away in the background. I used the same spot to light parts of the pier and its legs. These features were dark at the site, and their amazing detail had to be seen. The city light at the scene was sodium vapor, which creates an almost neon orange color on (my) film. My halogen lighting is also orange on film, though of a different quality.
All the Alley images are shot long after dark, although some sun can creep in in the form of moonlight. The effect of this light is mainly seen in the blue skies at night. When moonlight is mixed with a sodium vapor-filled sky, the result is a pink or purple hue.

So now you know my secrets, and as they say… now I must kill you…