I have recently been experimenting with latensification by use of low level light. It is neat...really neat. For those of you who are unfamillar with this technique I will explain what it is. Latensification in this context is not pre-exposure involving shadow support by adding density from exposure to reflected light from a gray card etc placed on say zones 0 thru 2. Latensification with low level is usable with film that has been exposed to light within the normal limits that does not require reciprocity correction. For most black and white film this would be from say 1/2 second thru 1/2000th of a second. Some films will preform outside of these limits without reciprocity compensation being required. Latensification with light can only be done of the film has been already exposed. So the negative is exposed normally with the camera. It has to be exposed to low level light for a minimum of 15 minutes. The purpose of doing this is make developable a silver crystal that has not received sufficient photons to become developable. What this does is to increase shadow film speed by 1 or more stops. It will also add a bit to film base fog. When used in this manner it has the effect one desires when using a compensating developer to increase shadow detail. However useful compensating development is it also tends to reduce shadow contrast. Low light latensification increase both shadow detail and shadow contrast and should work with any B&W film and developer. As an example, I mainly use 100Tmax. When used with Pyrocat HD I used a film speed of 64 before I started latensifying the film. Now I get full shadow detail at a film speed of 200. There is no gain in grain size. I have increased my development time by 5% to restore contrast...when you lift the bottom it is closer to the top.
What is required is tests to determine where to put the light and its brightness so that you get the maximum gain in shadow speed with minimum of fog as well as even coverage of the film. I have the light 12 feet from the film with the emulsion facing the light. The light being used is an old Kodak Brownie Darkroom Lamp using a green filter inline with a bulb dimmer. I have a 7 watt bulb inside the lamp. The light is substantially reduced with the dimmer. I cover all luminous dials when doing this. Elimination of stray light is very important. The safelight filter I would imagine could be of most any color if one is using a panchromatic film. I believe that the reason a green filter is so often used is not due to the film but rather due to human eyesight being very sensitive to green light.
Since stray light cannot be tolerated one must either stay in almost complete darkness for 15 minutes or more or be able to leave the darkroom without stray light getting in. My darkroom is in the basement, completely walled in and has a door that exits into the basement proper. I am not a good candidate to sit in the dark for more than 15 minutes doing nothing. What I do is to latensify my film after night fall. I go into the basement with a flashlight and close the door behind me. I enter the darkroom, close its door and turn on the latensifying lamp and make certain any luminous dials etc are covered. I turn off the flashlight hang the film with the emulsion facing the lamp. I find my way out in almost complete darkness...The latensifying light is no help in seeing where you are going. I exit the basement and come back the same way without any light being...NO FLASHLIGHT.. 30 minutes later. I turn off the latensifying lamp and find the film in the dark and then put it into my paper safe. Lights are turned on and I prepare to go thru my normal developing practices. If I wanted to do this to 400 speed film, I would have to hang the film 24 feet from the lamp...not an option due to size restrictions in the darkroom or reduce the bulbs brightness by a factor of 4 which is easily done.
If you go thru a bit of effort in testing I believe that you will find latensification a very rewarding practice.