Quote Originally Posted by Thomas Bertilsson View Post
This is not correct.

The common thing to do is to use a very weak light of green color, and only for a very short period of time. Green is the color that the human eye is most sensitive to, which is the reason for using it.
A standard safelight is used, with a weak bulb, and you inspect the film from about 3-4 feet distance for a few seconds.
This does technically fog the film, but not enough to make a practical difference.

After much practice you learn what the film should look like, and you learn to gauge how much more development a negative needs before you pull it and put it in the stop bath.

Films like TMax 100 are difficult to gauge, because of the incorporated dyes that are used for sensitizing as well as filtering.
I would like to add that not only is the eye most sensitive to green light but that many films have a dip in sensitivity in this region. Even so it is very important not to expose the film to the light until development is at least 50% completed. The self masking of the developed silver is an added safety factor.

The film should be inspected from the base side and not from the emulsion side. This technique takes a bit of experience to do well. The standard time/temperature method is actually more accurate in most circumstances.

A film can also be put in a pre-bath containing certain dyes to decrease the sensitivity of thee film allowing the use of a much brighter light.