Fluorescent bulb in safelight

I have made emulsions (ISO 40 ortho sensitive) under sleeved fluorescents while teaching workshops. Inevitably the emulsion is foggier than ones I make at home. Of course with students poking red safe-flashlights into the beakers, who knows how much fog that contributes, but I want to warn you that I have seen it once myself in a private session at one lab where I did it myself with no students.

The sleeved fluorescent, IMHO is leaky.

PE

Photo Engineer said:

The sleeved IMHO is leaky.

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The sleeved fluorescent tubes (really just tubes with a bit of plastic) can sometimes be a bit off but even the classic OC gels too don't age with honour. Fluorescent, of course, are NOT the problem. Its the filters. My general purpose lamp (and the general purpose lamp of a vast number of professional labs) is a Kindermann Dukalux SL Tanden
It uses compact PL 11-L lamps (20w each!). Would I use a fluorescent bulb in a Kodak Beehive safelight? Sure. Less heat would help the filter last longer--- remember(!) the filters need to be checked from time to time since they are consumables and not durables.

I've used an OC sleeved 20 watt white tube for years without problems at about 5 feet. It tests good for up to at least 15 minutes at that distance with papers designed for OC safelights (e.g. Multigrade or Polycontrast). It might be interesting to test it with an F20T12/GO gold tube. In my new darkroom, I'm migrating toward red safelights because the OC is not recommended for many of the east European papers. I'll let you all know what I find out.

Encapsulite makes flourescent tube safelights....Basically a regular long flourescent tube inside a red sleeve! Works fine. I had one when I lived in England, it was the cats meow.

I used a darkroom for 15 years that had sleeved fl. light bulbs and never experienced any fogging.

Probably would cuase problems, the others are right, the wider spectrum of a CFL could fog your paper very easily, go get yourself a 15-25 watt incandescent

Why risk it? Use incandescents.

Photo Engineer said:

The problem that I was taught to be concerned about in both cases you mention is that the light's output energy may exceed the density of the filter in a region that is unsafe.

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Its just a brighter light. If the light in the unsafe region is of too high a level there are two solutions 1) Use a higher density filter 2) Use a lower output bulb (or one of the special dimmable bulbs).

Take a fluorescent bulb with an integrated energy output of 10W, but a peak output at 450 nm (made up example) of 50w or greater. That 50 watt blue light will punch through the filter and fog photographic materials no matter what.

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That's a bit too much inappropriate allegory. 50 watts MIGHT fog but might not. A 10 watt incandescent bulb might fog some paper. Its just a question of radiation magnitude (level) and spectrum (frequency). Fl bulb spectra is quite similar to incandescent except their radiation below 500 nm falls off. This is part of what makes them so much more efficient for our application. A low pressure sodium bulb is even more efficient for traditional (and most variograde) B&W and colour papers since its emissions are just the sodium lines (its main one being 570nm which is the reason for the gap in colour emulsions) and totally inefficient for orthochromatic materials (typically photosensitive to around 600nm).

The same is true of the incandescent lamp if the light is too energetic.

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Correct. But also incandescent lamp are not just visually less efficient (radiation under 500 nm which we'd filter off) but also less energy efficient (produce more heat). Many of the materials used for darkroom filters are prone to either damage or quicker aging due to heat. That's why one typically does not want to use higher powered bulbs in safe lights. The higher the warm output the more prone the filter to deterioration (shorter MTBF). Fl lamps are cooler so using the same light output the entire system, I'd argue, is more reliable and safer. Another alternative (also very cool and energy efficient for this application) are LEDs (Amber or Red depending upon the filter chosen and/or selected photosensitive materials).

There is absolutely nothing wrong with using energy saving lamps in a safelight. As always one must test. Safelight are only safe when they have been tested and proven to be within a specific and well defined time period. Fl bulbs, however, do have one significant shortcoming (aside from environmental issues of disposal): they are not switchable. One can't turn them off and on quickly. This makes them unsuitable for those using enlarger automation meters that can't zero (or filtre out) the "noise" from the safelight--- there is no other reason to turn safelights off/on (either they are safe or they are not) during exposure.

Ed;

My post was merely meant as an example, not as proof or fact. Your advice to test is correct.

PE

What is to be gained experimenting with bulbs not intended for the fixture? Why not just use an incandescent that the filter is rated for?

The Jury is in for me...

One thing that is interesting is the variability in filter materials. Seeing that the best way to answer my question was to do the testing, I chose a common GE 10W CFL--and placed it in the Kodak beehive fixture and also the Model D 10x12" utility light. All used OC rated filters--and the test medium consisted of three varieties of Ilford VC RC and also FB Ilford Galerie #2.

I have three different iterations of the Kodak 5 1/2" OC filter. The oldest (and not used) consists of a paper filter sandwiched between two sheets of glass. I suspect that these were the type most vulnerable to fading and degradation--as this one has experienced that in its original factory packaging sleeve. The second, merely marked Kodak OC, is a deep orange (amber), and the newest (bought last year from B&H) is an odd yellowish-orange Cat. # 152-1483. The 10x12" is a Doran OC, whose output matches the deep orange (amber) Kodak. These latter two use filtering dyes that are integral to the glass or plastic substrate, and are likely much less prone to fading--if at all.

Test strips were exposed for 5-10-15 minute increments at 4 and 6 feet. Development was is fresh 1:2 Dektol. Long story short, no fogging with either the Kodak or Doran filters. All lights have now been converted to CFL, and working visibility is much better. Based on this I would like to try the Delta sleeve OC filter with a 24" Philips TL-950--but there is no way I am going to spend $65 for a piece of colored plastic...

Edz wrote: Fl bulb spectra is quite similar to incandescent except their radiation below 500 nm falls off.

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Not true. Incandescent lamps produce a fairly linear diagonal relative power distribution ranging from maximum (in the near IR range) at 760nm to nothing in the UVA segment at about 340nm. Tristimulus fluorescents on other hand produce a flattened and skewed bell curve that contains five to seven very sharp energy spikes. Nonetheless, for my purposes with Ilford products, the CFL has proven to be a viable alternative with better visibility than the incandescent lamp.

Patrick;

If incandescent lamps produce nothing in the UV segment, and Azo is only sensitive to UV and a tad of visible to about 420 nm, how come Azo is so sensitive to Tungsten light? It actually is quite sensitive and requres about 4 - 8 seconds exposure with 60W at 4ft or so. That is rather strong. If I put in a UV filter, I lose about 5 stops in speed.

PE

Photo Engineer said:

Patrick;

If incandescent lamps produce nothing in the UV segment,

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and Azo is only sensitive to UV and a tad of visible to about 420 nm, how come Azo is so sensitive to Tungsten light?

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Is not AZO a silver chloride paper with some sensitization? The spectral sensitivity of chlorsilber is blue sensitive. Looking at some of my old curves for Agfa's equivalent (Lupex) its 350nm to just over 500nm. Looking even closer I see that the sensitivity drops off below 400nm (near-UV). Lupex has its max. at 420nm. Tungsten bulbs do produce 420nm--- start in near UV at 360nm. So.. sure.. sensitive to Tungsten light.. Makes sense since the contact copiers of the day used Tungsten bulbs...

As you say, tungsten produces in the UV, 360 nm. UV is considered to start at 400 nm. Lupex is, as you say, a Chloro-Iodide which is sensitive into the visible to 500nm and has some spectral sensitivity.

My Azo type emulsion has no Iodide, and no sensitizing dye! Therefore it is not very sensitive into he visible and cuts off at about 400-410 nm but still is 'fast' to a 60 watt incandescent bulb.

PE

UVA starts at 400nm--and as I stated, "ordinary" incandescents dependably output UVA to about 340nm. Those lamps that are rated higher output-energy efficient and halogen types will radiate stronger and shorter wavelengths--and as such often have UV blocking materials incorporated into the glass envelope as many fluorescent devices do. The higher the wattage, hotter the filament, the more UV emission. It is my understanding that many of the name brand bulbs have incorporated this filtering for several years now to reduce fading of exposed surfaces and textures.

Try some red LED lamps. Look for something with an E27 base (Standard Edison base used in the USA). I've got some "Nanowatt" or something or other LED lamps that I picked up. I've got them in reading lamp housings, and at 1 watt, they are good for spot lighting in the darkroom, like over developer trays. I'd suggest finding something higher powered, like 3 watts perhaps. I'll get one some time and it should light a fair work area. And at about 630 nm, they should be safe for all non-panchromatic or IR materials.