Fluorescent bulb in safelight

Roger Pellegrini

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Just bought a used Kodak safelight and it came with a 25 W screw mount fluorescent bulb. I will have to test it, but has anyone had any experience with these behind an orange filter?
 

DWThomas

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You may also want to consider that many CFLs, at least those I've bought, are specified as not usable in a sealed fixture. I suppose the worst that can happen is the bulb burns out prematurely, but that's been one of my concerns about the intended wholesale switchover from incandescents.

DaveT
 

Murray@uptowngallery

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Afterglow can supposedly remain for up to 20 minutes, too dim for you eyes to see, but enough for some films to see. I assume the afterglow would be at visible wavelengths because that's the purpose of the phosphor (create visible light when the lamp produces UV in the internal arc/plasma.)

By the way, 2007 was the 70th anniversary of fluorescent lighting.
 

nworth

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Most modern compact fluorescents - the kind with screw bases - have phosphors that do not have the afterglow common with older cool white fluorescent tubes. Note, however, that a 25 watt compact fluorescent is roughly equivalent to a 100 watt incandescent in light output. That is a lot more light than is usually recommended. Although the light is superficially similar to incandescent, the spectrum of the compact fluorescent is actually much different than an incandescent, so you can't really compare them for safelights. You might consider replacing the 25 watt bulb with a 9 watt unit or even smaller. In any case, do some thorough safelight tests with your papers to see how much safelight exposure you can get away with.
 
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Roger Pellegrini

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Thank you. I did seem rather bright to me. I am just going to take it out and put in an incadescent bulb.
 

photobackpacker

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My concern would be that the color spectum of the CFLs is vastly different than that of incandescent bulbs.

The safelight filters, in combination with the incandescent light source, have all been developed to produce light in a narrow spectrum. I have never tested it but my instinct would be that the greenish cast to the light produced by CFLs would cause a change in the light being produced making the light "less safe".

I would do a very thorough test using the Kodak procedure.
 

Photo Engineer

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PeterB said:
What is the problem with afterglow if the glow is behind the safelight filter ?

Peter
Click to expand...


What if you were doing 2 rolls in sucession. First is pan using a dark green safelight and second is infra red (no safelight). You do #1, tank it, turn off the safelight and reel up the IR film but afterglow will fog it.

In fact, afterglow can even be a problem with tungsten when IR is concerned.

But, a more practical example is high speed pan with no safelight. Lets say you are printing with an OA filter and then decide to run some HS pan so you turn out the safelight. The afterglow can get to the HS pan film.

Just thoughts, but I believe them to be valid.

In addition, the odd emission spectum of most fluorescents make them brighter at some wavelengths than others thereby defeating the purpose of the safelights assumption that the source bulb will put out a continuous spectrum from 400 - 700 nm (plus a tad of UV and lots of IR). Fluorescent bulbs put out more UV and less IR.

PE
 

Murray@uptowngallery

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1) Hmm, Tesla...

OK, maybe someone made an politico-centric claim about 1937. Not uncommon for one country to have ignore another's accomplishments...we've seen that historically...

Maybe it was for a specific type of lamp/ballast combination. I'll never find my reference, so thanks for correcting my misinfo.

2) I was going to say 'good point' about afterglow behind 'safe' filter...but then I remembered one uses a safelight with materials that are safe under safelight, and turns it off for materials NOT safe under safelight...like panchro film...
 

PeterB

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Photo Engineer said:
What if you were doing 2 rolls in sucession. First is pan using a dark green safelight and second is infra red (no safelight). You do #1, tank it, turn off the safelight and reel up the IR film but afterglow will fog it...... PE
Click to expand...

Great points !

Peter
 

PHOTOTONE

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Ole said:
Can't have been - Nikola Tesla displayed fluorescent lights at the 1893 World's fair in Chicago.
Click to expand...

Maybe the poster means "commercially marketed" fluorescent light.
 

PHOTOTONE

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Murray@uptowngallery said:
1) Hmm, Tesla...

OK, maybe someone made an politico-centric claim about 1937. Not uncommon for one country to have ignore another's accomplishments...we've seen that historically...
Click to expand...

Tesla lived and worked in the USA, and was a US Citizen, although foreign born. While he did demonstrate fluorescent light, it was not marketed as a commercial product for many years later.
 

Reinhold

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Troy said:
I have used fluorescent tubes in safelight sleeves for years. I have had zero problems.
Click to expand...

Just for the heck of it, I took a reading of afterglow with a Pentax digital spot meter held up against a bare 4' warm white flourescent tube and took a reading within 5 seconds of turning it off (in my darkroom, of course).

Wanna guess what it read??? Zeeeero.

Ok, lets assume that the light was actually E.V. 0.9, and couldn't trigger the meter to respond with a positive reading. How long would a medium speed panchromatic film have to sit on a countertop (4 feet below the light) before it would show noticeable fog?

Also... afterglow diminishes with time... I can't visually see any glow after a minute or so, even with eyes that are fully dark acclimated. When I process 400 speed film or Konica 750 IR film, I wait 2 minutes before opening the wrapper. Been doing it for nigh onto 20 years now...

I routinely latensify film in the same room (using a #3 filter in a Kodak beehive safelight) for 16 minutes, and have yet to get even a hint of uncontrolled fogging from fluorescent lights.

Afterglow is a not a bugbear in my darkroom.

Reinhold
 

srs5694

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I strongly suspect that this varies a lot from one bulb/fixture to another. My darkroom has overhead fluorescent tubes. (They were there when I moved in, before I converted the room to a darkroom.) I can't detect any afterglow with my eyes, even with all other lights off in the room. I've got compact fluorescent bulbs in most fixtures in my house, including my bedroom. When I go to bed, I most definitely do see an afterglow for a minute or two. I'm about the same distance from the bulbs in both cases, but of course my eyes are hardly scientific precision instruments.
 

Kilgallb

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PeterB said:
What is the problem with afterglow if the glow is behind the safelight filter ?

Peter
Click to expand...

In my case, I usually do a print session then finish of with developing my film.

So you turn off the safelight and load film into a reel with the afterglow fogging your film.
 

Papa Tango

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Will the spectral power distribution of a CFL affect the output of a properly made safelight filter, such as a Kodak OC. The whole purpose of a filter is to allow only those wavelengths below a certain point--the OC has a very sharp cutoff at about 625nm to shorter frequency wavelengths.

There should be no issue with afterglow--as the issue in the past involved older single halophosphor coatings. This may be an issue with very cheap cool white linear lamps that have a CRI of less than 80, but not higher CRI or compacts. The reason for this is that the newer lamps use a triphosphor mix in order to achieve a color spike in the blue, green and red segments of the spectrum. The tiny amount of residual glow from these phosphors decays very quickly, and would be diminished by a factor of at least four due to the density of the filter material.

My question though is this. Has anyone used an equivalent 10 watt (eq to 40W incandescent) or a 40W incandescent in a standard OC light? I have a need to throw light from a low angle from ceiling to easel at about 6' to illuminate a meter and timer. Overhead does not work because the big Beseler dichro head is in the way. Any thoughts?
 
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Photo Engineer

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

PE
 

keithwms

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Oh good, another opportunity for me to preach about mercury in fluorescents!

The mercury vapour present in these lights give rise to very strong spikes in the UV, at various wavelengths in the visible spectrum, and into the IR.

One might think: well, the safelight filter cuts out everything below red. That is not quite true: it cuts out almost everything but not all. There is the risk that the filter allows some of the stronger lines (e.g. 546 nm) through. If this is found true, then doubling or tripling the filter would probably do the trick.

Along the lines of what Ron is saying, the issue with the mercury spectrum is that the power is not evenly distributed across the wavelengths like it is for an incandescent bulb. In a fluorescent containing mercury, there are very high power spikes at particular wavelengths.

So... as advised, test!

P.S. this is the first I've heard about long-term afterglow. Phosphorescence? If not then I suppose that it would be quite far into the IR, probably further than a meter can see. I'll have to read up on this. I have seen short-term afterglow but expect nothing but mid IR stuff after a few seconds. If anybody has good links...
 
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Papa Tango

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Good catch, PE. There are going to be two main energy spikes at approximately 540nm and 570nm--and the order of magnitude will be over four and three times the relative energy of the base curve, respectively. The 570nm is likely not to be as great a concern, as its energy level is within the relative energy design slope of an incandescent device, but the 500-525nm certainly would be much more than the design of the filter was intended for.

I have re-edited my opening statement accordingly to your answer
 

nworth

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I am building a new darkroom, and I intend to try using fluorescent lamps as safelights for paper. In my case, I intend to use red ceramic lamps encased in medium red (1% cutoff at 590 nm) gel tubes. Most of the red phosphors now in use have a strong peak (from Eu doping) at around 630 nm, with little light outside the red region. The red filter of the ceramic tube should effectively cut out the blue and UV that may exist, and the enclosing gel tube should further reduce any spurious output. A possible problem is that not all fluorescent tubes are made the same way. The red tubes can use at least three different phosphors, and the red tube filter (red fluorescents always have red tubes) may vary. You can get different results from different bulbs. On paper, the design looks like it will work. The tubes will be about 8 feet from the working surfaces, so the brightness should be OK. Needless to say, I will do a thorough safelight test. If it doesn't work, there are enclosing tubes available (at a much higher cost) that imitate a Wratten No. 1 safelight with a 40 watt standard cool white bulb inside.
 
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