When is Film Light Safe?

[Doremus Scudder]

An elaboration to clear up some possible confusion for the OP:

"Light-sensitive" means different things:

Panchromatic films are sensitive to all visible wavelengths of light plus some UV. The weakest sensitivity for these films is usually in the green area, hence the possibility of using a weak, dark green safelight for a limited time to inspect a developing negative. The small exposure doesn't expose the film to enough light to fog it. If you expose the film too long to the same safelight, however, it will fog the film, as oldtimermetoo found out. The link above to MichaelandPaula.com is the best guide for developing by inspection that I know of. Most of us prefer to use time/temp. and keep the film in total darkness. (Question: just why do you want to inspect your film while developing anyway?)

Orthochromatic film is sensitive to blue and green (and some UV) but not red. Therefore, it can be processed under a red safelight. Again, even too much "safe" light will fog the film; the safelight needs to be dim enough and the exposure short enough so that the film's exposure threshold is not reached.

Older photo emulsions (think plates/films from the 19th century) are sensitive to only blue and UV. These are usually referred to as "blue-sensitive" and can also be developed under a suitable safelight.

Emulsions on graded photo paper (i.e., not variable-contrast) are like these older emulsions; sensitive to only blue and UV. Safelights for these papers are usually amber or red.

Variable contrast papers are sensitive to blue and green, so an appropriate safelight, usually red, is needed. Amber is sometime used too if the paper's sensitivity allows.

Safelights are rarely 100% safe. They pass other wavelengths in addition to the desired ones. Therefore, it is a good idea to limit the exposure even to a safelight. Safelight tests are a routine part of setting up a darkroom.

Exposed and developed = Image; Exposed and fixed = No Image

Light-sensitive film gets exposed when struck by enough light of the colors it is sensitive too. This makes a latent image. This image needs to be turned into metallic silver somehow before it's visible. There used to be materials that would form a silver image with exposure to light alone (printing out paper or POP), but these are no longer commercially available. Nowadays, you need a chemical developer to do the job.

After the developing step, we stop the chemical reaction with a stop bath. Even though the development is stopped at this point, the film is still light-sensitive. You could expose it to light and put it back in the developer and develop more parts of the film that weren't exposed the first time. It is the fixer that removes the undeveloped, but still light-sensitive silver halides so that the film can't be exposed any more.

Fixer also removes exposed, but undeveloped silver halides. If you take exposed film and put it straight into the fixer, it will come out blank, even if you've exposed it to room light. Theoretically, therefore, you could expose film to light after the stop bath stage with no ill effects. The remaining silver halides will get exposed, but you can then just fix them out, since they are not developed. In practice, most of us keep the film in the dark till at least halfway through the fixing stage for a couple of reasons. First, if the stop is not complete, the remaining active developer will go to work on the newly-exposed silver halides, "solarizing" the image or, worse, fogging it. Second, if the light is strong enough, some film emulsions will fog a bit even without developer. Better to play it safe.

BTW, solarizing prints is used by many printers as a special effect; the print is exposed for a very short time to overall exposure (e.g., turning on the room lights) for a very short time while in the developer tray. Google for some images.

Hope this helps,

Doremus

 

[BMbikerider]

I have found in the past a dark green light is virtually useless. The same applies to RA4 colour paper under a green light. It can be circumvented by using a safelight which employs a Sodium Vapour bulb and that makes printing a little bit easier. However there is no mention nor have I heard anyone say these sodium vapour bulbs can be used with film because film is than more sensitive.

 

[Harry Stevens]

I suppose if you are that desperate you could try strapping on some military grade night vision goggles,me I will keep my negatives in the tank.

 

[Bob Carnie]

I really appreciate the responses, but I am confused. Isn't my question a matter of science and not opinion? How can there be different answers to the same question?

Because normal safelight will indeed fog film, the poster who said you could neglected to point out the specific wavelength of light to be able to inspect.
Some people use special light and infared goggles to do this.

As others may point out if you are using a ortho film then you may be able to do so with a specific red filter.

I would recommend not using any inspection method but rather use time temp method of development. But this is my opinion only and there are may options for you to pursue.

 

[darkroommike]

• The reason that most recommendations for DBI recommend waiting until the development is at least half completed is that the film is much less sensitive to light at that point (sort of desensitized by development).
• The reason that a dim green safelight (and when the experts say dim they mean really dim!) is used with panchromatic film is not that the film is less sensitive to green light but that the human eye is more sensitive to low levels of green light than any other color.
• For orthochromatic films a somewhat brighter red light is used, ortho films are relatively insensitive to red safelight but there's red and there's red, best to err on the side of caution even with ortho materials.
• By the end of the development time the film is very much less sensitive to light and some types of tube processing (BTZS and home made similar systems) actually recommend transferring the tubes to the stop bath under low room illumination, it works because the film is still semi-shielded in the tubes so the intensity of exposure is very low and no further development takes place since the film is immediately in the stop.

I have also had students drop film reels onto the sink when pouring out developer when they did not properly secure the "funnel lid" on a Paterson tank, always embarrassing, but no real harm if they get the reel back into the tank immediately, lid up and into the stop bath. There may be some small amount of physical development as PE and others have suggested or a small amount of fog, but I have never noticed any real, gross evidence that the film is "completely ruined".

 

[Photo Engineer]

On a scientific basis then, here are the dye types from blue only through ortho to pan to ir to far ir.

And for color paper it is a WR13 dark amber that should be used, not green. Paper is sensitized quite differently than film is.

PE

 

[BMbikerider]

I suppose if you are that desperate you could try strapping on some military grade night vision goggles,me I will keep my negatives in the tank.

I had never thought of that, the night vision goggles that is. Quite novel! There again a tank is easier.

 

[Bill Burk]

PE,

Explain more about the printing out possibility. Because that's all I didn't consider when I think of what happens if you take film out of developer and put it in (slight acid) stop and then (acid) fix...

The film spent maybe 10 minutes in developer and the highlights reached a density of maybe 1.5 and then suppose you take the whole film into the light... additional density and fog density will immediately begin to grow... and once you stop the developer you might say 15 to 30 seconds of development time elapsed before all developing activity stops...

What amount of fog might that add? I'd guess maybe 0.05 (barely measurable).

But printing out to metallic silver? That is something I didn't think of.

 

[Bill Burk]

I had never thought of that, the night vision goggles that is. Quite novel! There again a tank is easier.

Night vision devices, generation 1, are relatively inexpensive and they are useful. Toys are also available that are interesting and cheaper.

 

[Truzi]

An elaboration to clear up some possible confusion for the OP:

"Light-sensitive" means different things:

Panchromatic films are sensitive to all visible wavelengths of light plus some UV. The weakest sensitivity for these films is usually in the green area, hence the possibility of using a weak, dark green safelight for a limited time to inspect a developing negative. The small exposure doesn't expose the film to enough light to fog it. If you expose the film too long to the same safelight, however, it will fog the film, as oldtimermetoo found out. The link above to MichaelandPaula.com is the best guide for developing by inspection that I know of. Most of us prefer to use time/temp. and keep the film in total darkness. (Question: just why do you want to inspect your film while developing anyway?)

Orthochromatic film is sensitive to blue and green (and some UV) but not red. Therefore, it can be processed under a red safelight. Again, even too much "safe" light will fog the film; the safelight needs to be dim enough and the exposure short enough so that the film's exposure threshold is not reached.

Older photo emulsions (think plates/films from the 19th century) are sensitive to only blue and UV. These are usually referred to as "blue-sensitive" and can also be developed under a suitable safelight.

Emulsions on graded photo paper (i.e., not variable-contrast) are like these older emulsions; sensitive to only blue and UV. Safelights for these papers are usually amber or red.

Variable contrast papers are sensitive to blue and green, so an appropriate safelight, usually red, is needed. Amber is sometime used too if the paper's sensitivity allows.

Safelights are rarely 100% safe. They pass other wavelengths in addition to the desired ones. Therefore, it is a good idea to limit the exposure even to a safelight. Safelight tests are a routine part of setting up a darkroom.

Exposed and developed = Image; Exposed and fixed = No Image

Light-sensitive film gets exposed when struck by enough light of the colors it is sensitive too. This makes a latent image. This image needs to be turned into metallic silver somehow before it's visible. There used to be materials that would form a silver image with exposure to light alone (printing out paper or POP), but these are no longer commercially available. Nowadays, you need a chemical developer to do the job.

After the developing step, we stop the chemical reaction with a stop bath. Even though the development is stopped at this point, the film is still light-sensitive. You could expose it to light and put it back in the developer and develop more parts of the film that weren't exposed the first time. It is the fixer that removes the undeveloped, but still light-sensitive silver halides so that the film can't be exposed any more.

Fixer also removes exposed, but undeveloped silver halides. If you take exposed film and put it straight into the fixer, it will come out blank, even if you've exposed it to room light. Theoretically, therefore, you could expose film to light after the stop bath stage with no ill effects. The remaining silver halides will get exposed, but you can then just fix them out, since they are not developed. In practice, most of us keep the film in the dark till at least halfway through the fixing stage for a couple of reasons. First, if the stop is not complete, the remaining active developer will go to work on the newly-exposed silver halides, "solarizing" the image or, worse, fogging it. Second, if the light is strong enough, some film emulsions will fog a bit even without developer. Better to play it safe.

BTW, solarizing prints is used by many printers as a special effect; the print is exposed for a very short time to overall exposure (e.g., turning on the room lights) for a very short time while in the developer tray. Google for some images.

Hope this helps,

Doremus

There are a lot of good posts in this thread, but this one is an excellent and comprehensive explanation. This post is the kind of content that would be great for a resource/FAQ we could refer people to if we had one.

 

[Photo Engineer]

Any silver halide will darken in light. This is caused by formation of silver metal in a process called "printing out". It was used by printout papers years ago in which the high speed (for this purpose) emulsion was exposed to light under a negative to give an image. Afterwards a treatment would stabilize it to further change. Well, this is the same as what happens with overexposure to a safelight during processing with todays high speed emulsions. The higher the speed, the more the printout. And, exposure during development causes faster fog growth.

In any event, take a piece of film and develop it, unexposed, in total darkness and then stop. Cut it in half. Expose 1/2 to light and keep the other dark. Then fix wash and dry both. Measure the density. The difference is printout. Now, do the same, but use your safelight.

PE

 

[Photo Engineer]

The long standing banter between myself and Bob Carnie involves the difference between Solarization (an in-camera process done while the film is dry) and the Sabbatier Effect (done in the darkroom while the film or print is wet). The result is similar but not exactly the same. This common error in terminology is shown above in the post by Doremus Scudder. I apologize for the correction, but it is a real difference and needs to be pointed out if we are to remain technically correct and get the results we expect.

PE

 

[Leigh B]

On a scientific basis then, here are the dye types from blue only through ortho to pan to ir to far ir.

Hi PE,

Thanks for those, but they're incomplete.

They stop at 400nm, the upper end of blue. They don't continue into the UV range.

The first two spectra are still at full sensitivity at 400nm.
It would be interesting to see their response as you approach 300nm.

- Leigh

 

[cliveh]

(Discussion in '(there was a url link here which no longer exists)').

You can use a dark green dim inspection filter for brief periods of time.

 

[Photo Engineer]

Hi PE,

Thanks for those, but they're incomplete.

They stop at 400nm, the upper end of blue. They don't continue into the UV range.

The first two spectra are still at full sensitivity at 400nm.
It would be interesting to see their response as you approach 300nm.

- Leigh

Since most films are overcoated with a UF filter, and most lenses are UV filter coated, then there is little need for testing that for all practical purposes. However, I have seen such curves and the blue end just continues the "arc" of sensitivity to the left past 400 nm. In fact, I rarely use a UV filter on my spectrosensitometer and can see down to about 380 or so with my chloride emulsions.

For all practical purposes the chart I posted is sufficient. It leaves out the sensitivity to nuclear particles as well.

PE

 

[Gerald C Koch]

I have found in the past a dark green light is virtually useless. The same applies to RA4 colour paper under a green light. It can be circumvented by using a safelight which employs a Sodium Vapour bulb and that makes printing a little bit easier. However there is no mention nor have I heard anyone say these sodium vapour bulbs can be used with film because film is than more sensitive.

You have to allow 20 to 25 minutes for your eyes to become accustomed to the dim green light. But once this happens you would be very surprised by how well you can see. I have hyper-sensitized film several times under similar conditions. Our primate ancestors evolved in the forest tree canopy and so our eyes are very sensitive to green light.

 

[Photo Engineer]

I'll repeat again that you cannot use anything but an AMBER safelight (WR13) with color paper. Green will fog it.

PE

 

[removed account4]

hi PE
this post is in the Black and White sub forum ...
that might be the reason people aren't worried about color paper and amber bulbs.

 

[Doremus Scudder]

The long standing banter between myself and Bob Carnie involves the difference between Solarization (an in-camera process done while the film is dry) and the Sabbatier Effect (done in the darkroom while the film or print is wet). The result is similar but not exactly the same. This common error in terminology is shown above in the post by Doremus Scudder. I apologize for the correction, but it is a real difference and needs to be pointed out if we are to remain technically correct and get the results we expect.

PE

PE,

Thanks for correcting my sloppiness and there is certainly no need to apologize. I do indeed know the difference between true solarization and the Sabattier Effect, but have succumbed to the common usage of the term solarization for both. In my defense, Wikipedia lists the Sabattier Effect under their page on solarization. The article even states, "The term [solarization] is synonymous with the Sabattier effect when referring to negatives." Maybe it is worth elaborating on, however.

True solarization is a reduction of sensitivity due to extreme overexposure and affects the latent image. The extremely overexposed area develops less than expected due to the loss of sensitivity due to overexposure. Both AA and Minor White have images titled "Black Sun" in which the disc of the sun is rendered black due to exactly this overexposure.

The Sabattier Effect in printing results when a partially-developed print is given an overall exposure to actinic light and is then developed further. The silver image already developed masks areas of the print from the overall exposure and the result is a "pseudo-reversal" of tones in the print, since the light areas of the print, which were exposed to the overall exposure can become quite dark, while the areas masked by the already-developing silver image turn out lighter in the final print. The Sabattier Effect on negatives is similar, but since it happens to a negative image, the resulting print made from the negative has an opposite distribution of tones.

I imagine that "solarization" will still be common parlance for the Sabattier Effect, especially in printing no matter what we do. I've embraced it, with reservation or explanation to disambiguate when needed.

Best,

Doremus

Best,

Doremus

 

[Photo Engineer]

hi PE
this post is in the Black and White sub forum ...
that might be the reason people aren't worried about color paper and amber bulbs.

In an earlier post, someone brought up color. I was answering that post.

PE

 

[dE fENDER]

Night vision googles with infrared light will cause fogging on some emulsions, but it still possible to get chemical desensitizer, like pinacryptol. And develop with green safelight after desensitizing bath.

 

[Photo Engineer]

Desensitizer use is very difficult with some modern films. The modern dyes are hard to replace and thus give colored stains. Also, these desensitizing dyes can cause speed loss and do slow development rate.

PE

 

[pentaxuser]

I think I am a little confused here but here's what I think the consensus is :When you have nearly reached the development time you think is right, you can add stop bath to stop development but if you take the film out of the tank to inspect under say a reasonable safelight intensity such as an amber safelight which is OK for paper then decide that development in the highlight areas is not complete, you can replace the tank lid, then wash with water to rid the film of the stop and continue development, safe in the knowledge that the shadow and midtones will not have been affected by the safelight as development there has ceased. However the "safelight" will have affected the highlight areas to an extent, so you are having to take this "unknown" into account when deciding how much longer to develop. It will NOT be the case that nothing has changed

Sp what you cannot expect is that nothing has changed for that period of inspection but how much has changed is unknown. So it may not be a controlled situation. The outcome remains problematic and while an inspection under a light intensity in which you can really see well enough to judge is possible such as it might be with an amber safelight, it introduces the unknown of further development while under the safelight.

Please note I have excluded in the above example a very dim green light which has no effect on the film but means being in the darkroom for maybe 30 mins with only that light on so you have to wait before adding developer unless the developer time is as long as 30 mins and of course means working by feel until your eyes are fully accustomed to the green light. Even then it might require quite a long time before you had acquired the necessary skills to recognise under very dim light what constituted a properly developed film .

Thanks

pentaxuser

 

[Gerald C Koch]

If you wish to develop panchromatic film by inspection you must use a green safelight of low intensity. Because the human eye is most sensitive to green this incurs the least chance of fogging. Due to the self masking effect of a partially developed negative it is best to do this after development is at least half completed. An amber safe light should never to used for film. A red safe light can be used for orthochromatic film.

When developing by inspection it is helpful to use two safelights. One for general illumination and the other situated close to the film say 2 to 3 feet. The one for general illumination should allow the user to see obstacles and avoid bumping into things but little other illumination. This second light is best used with a foot switch so it can be turned on for very brief periods to check the extent of development. Most of the time this second lighti is left off. Whenever I have developed by inspection this system has worked very well.

 

[Photo Engineer]

Do not use an amber safelight for anything but color paper. That is a WR13.

Use green only, and don't resume development after a wash or stop as they alter the way development takes place.

PE