Shooting B&W Film Using CFL Bulbs?

The weather has been bad here for the past week, so I'm thinking of shooting some B&W film indoors using CFL (Compact Fluorescent Light) bulbs so I can test some of my film cameras' light meters and shutter speed accuracy.

 

The film I want to use i s B&W Kentmere 100 35mm film.

 

Anything I should be aware of?

 

Thanks.

Broad spectrum high frequency CFLs with a high CRI shouldn't be an issue. I use to do it before I went whole hog on strobes.

 

I'm not sure if there are any still out there in CFL form, but you can have issues at higher shutter speeds(anything over the flash sync speed) with fluorescent lighting with 60hz magnetic ballasts.

 

Just remember that the spectrum of fluorescent lighting is "notchy" and not Gaussian like incandescent(or the sun). It shouldn't make a big difference with panachromatic film, or at least I've never run into trouble with it.

... so I can test some cameras' light meters and shutter speed accuracy.

 

Hi, I wouldn't trust em if you're gonna be critical about the metering.

 

CFLs are most likely just a sparse handful of spectral spikes with respect to the light output. Now this should NOT be a problem with respect to photographing on b&w film. My only concern would be as to whether the exposure meter gives an accurate prediction as to the effect on film.

 

I'm saying this as someone who is familiar with the ANSI standard (nearly identical to ISO) for exposure meters; these standards date back to the 1970s to the best of my recollection. They were essentially based on continuous spectrum light sources (similar to daylight or tungsten). I've also looked at spectral graphs on a number of fluorescent lamps, including CFLs. The CFLs that I've looked at have all been in the class of "energy-saving" fluorescents, having a small number of spectral spikes intended to be effective for human vision. So from this, there is really no guarantee of agreement between the meter vs exposure on film. Might be close, maybe not, but no guarantee either way.

 

If I were doing such tests, I'd get at least a couple shots under outside lighting to establish the meter to film-exposure correlation. If I couldn't do that, I'd either use tungsten lighting, or at the very least, an old-style non-energy-efficient fluorescent. Once you've established an error factor between "natural light" and the CFL, it'll probably stay consistent for each individual meter.

Hi, I wouldn't trust em if you're gonna be critical about the metering.

 

CFLs are most likely just a sparse handful of spectral spikes with respect to the light output. Now this should NOT be a problem with respect to photographing on b&w film. My only concern would be as to whether the exposure meter gives an accurate prediction as to the effect on film.

 

I'm saying this as someone who is familiar with the ANSI standard (nearly identical to ISO) for exposure meters; these standards date back to the 1970s to the best of my recollection. They were essentially based on continuous spectrum light sources (similar to daylight or tungsten). I've also looked at spectral graphs on a number of fluorescent lamps, including CFLs. The CFLs that I've looked at have all been in the class of "energy-saving" fluorescents, having a small number of spectral spikes intended to be effective for human vision. So from this, there is really no guarantee of agreement between the meter vs exposure on film. Might be close, maybe not, but no guarantee either way.

 

If I were doing such tests, I'd get at least a couple shots under outside lighting to establish the meter to film-exposure correlation. If I couldn't do that, I'd either use tungsten lighting, or at the very least, an old-style non-energy-efficient fluorescent. Once you've established an error factor between "natural light" and the CFL, it'll probably stay consistent for each individual meter.

 

Thanks for the in depth explanation. I'll just wait for good weather so I can get outside. It's gotta clear up sometime...

You're welcome. In the meantime, if you have enough light coming in the window that should be fine. Or you could probably just do your testing with the CFLs now, then at some point in the future just find the correlation between the CFL vs natural light; it's probably just an adjustment to the ISO film speed. Best of luck.

Surely any difference between meter-reading and film exposure would be down to a difference between the spectral response of the film and the meter sensor?

 

Regardless of the spectrum of the light source, if both film and meter have identical spectral response curves, then they'll respond identically. Although the subject colour could have a noticeable effect if incident metering was used, but the same would be true with a black-body spectrum.

 

Anyway, I think this whole thing is being over thought. Photo CFLs are designed to give acceptable results in colour, so I see no reason why the much sloppier exposure tolerance of B&W film shouldn't give good results too.

Surely any difference between meter-reading and film exposure would be down to a difference between the spectral response of the film and the meter sensor?

 

Yes, I certainly agree. If you have first-hand knowledge of any specific meters that match any film response, I'd love to hear about it. The meter standards certainly don't call for it. It would take at least a carefully designed filter pack over the sensor.

 

As I said, the meter/film agreement under CFL might be close, or maybe not. But if one is doing careful testing of film exposure based on metering, using CFL light sources is a pretty shaky way to do it. Now if your criteria is just to get a useable negative, probably no problem.

 

Anyway, I think this whole thing is being over thought. Photo CFLs are designed to give acceptable results in colour, ...

I don't know why you're bringing color photography into this, but if you remember the last time you pushed this idea, I refuted based on my substantial testing with a handful of CFL systems claiming "photo quality." When pressed to substantiate your position, here's what you said:

 

I make no claim that CFL lamps are perfect, or even halfway decent in colour rendering. I'm just pointing out that they don't have to be short on brightness. And that if the OP already has softboxes and luminaires designed to take CFL lamps, then fitting higher power tubes is an economical solution.

 

The claim of some CFLs being "photo quality" is made by their manufacturers and sellers, not by me.

Selenium and CdS are not close to the full visual spectrum, but were common for light meters for many years.

CdS has a bandgap of 2.42eV, or about 513nm, so blue and just a little green sensitive.

 

Silicon goes down fairly far into the IR, but with appropriate filter could be pretty close.

I don't know what filters they actually use on Si light meters.

 

In any case, fluorescent lamps have some mercury lines in the blue and green,

and phosphors to fill in mostly red. The phosphors are reasonably wide spectrum

compared to the Hg lines.

 

Cool white and similar lamps have much less red, give more lumens per watt,

but don't give as good color rendition. Warmer lamps are likely close enough

for black and white film, and probably also close enough for metering.

People have used lightmeters with tungsten lighting for years with no fuss, and the spectrum of incandescent lamps is nowhere near that for which a meter (or panchromatic film) is calibrated, being very red heavy and almost totally lacking in blue.

 

Like I said, this whole thing is being overthought. The tolerance for a photographic exposure is as wide as a barn door by normal measurement standards. One third of a stop is +26%/-21%, and half a stop is +41%/-30%. It's not exactly rocket science to measure light to that sloppy accuracy.

CFL's are no different than linear tube fluorescent devices, in that they radiate the majority of their light output loaded into three or four narrow peaks. See here: LED vs CFL Bulbs: Color Temp, light spectrum, and more

 

Most of the energy of a daylight or so-called "full spectrum" lamp is in the red and green areas of the spectrum. Depending on the film you choose, and the type of sensor your light meter uses (and its spectral sensitivity) can seriously affect the resulting ISO rating--and the contrast performance of the film.

 

For more regular use, the new LED lamps are the better choice, as they have a smoother spectral performance curve and more consistent output within that curve.

People have used lightmeters with tungsten lighting for years with no fuss, and the spectrum of incandescent lamps is nowhere near that for which a meter (or panchromatic film) is calibrated, being very red heavy and almost totally lacking in blue.

 

Ok, I wasn't gonna bother digging up the ANSI standard, but rather than risk giving a bad answer due to my shaky recollection, I did.

 

The bottom line is that the ANSI meter standard specifies a calibration point (color temperature) of 4700 K. (For reference this is between "tungsten" and "daylight," about 2/3 of the way towards daylight.

 

But the meter must also read properly, within a tolerance, for a tungsten light source. Here is an excerpt from the standard, "A tungsten lamp operated at 2854 K and the 4700K source described in 3.6 shall be used."

 

I think it would be fair to say, generally speaking, that an exposure meter IS calibrated for tungsten light. This is why, after stating that I was familiar with the ANSI standard, I said that a tungsten light source was one of the options that I would consider testing with.

 

The CFL lamps, though, are a completely different animal. They are in the general class of what I call energy-efficient fluorescent lamps, and they are much different from the old style fluorescents such as "cool white," or "deluxe cool white," and that sort of business. They are lacking a broad spectral coverage, being made up mainly of a handful of spectral "spikes." This is a way to get a high efficiency, by putting the spectral output where the human eye is most sensible. The first time I seriously looked at these, for purposes of color portrait photography, I thought, how can such a lousy spectral makeup get such a high value for CRI (color rendering index, a measure of how well colors are reproduced)? The answer SEEMS to be that the lamp designers have "gamed" the system, designing for a high score on the specific test used.

For more regular use, the new LED lamps are the better choice, as they have a smoother spectra

 

I pretty much agree, but still have reservations about using them when accurate color reproduction is needed. To be honest, I don't recall if I actually tested any of them or not, but I'm pretty certain that they can't pass muster for high quality portrait work. So-so color, or motion picture work, sure. The issue is the big spectral dip just off the bluish component.

 

If the lamp designers come up with a phosphor, or whatever, to fill in that spectral dip, I think these will be a nearly ideal light source.

 

Just as a note to people unfamiliar with modern "white LEDs," the output is not strictly LED. Rather, they have buried a set of phosphors into the package where the LED causes them to emit. So they are, in a way, a sort of hybrid fluorescent lamp.

Indeed. Both the newer daylight and full-spectrum lamps (and they are anything but either...) can be quite variable. Going back through the decades, standard halophosphate linear tubes marketed as 'warm', 'cool', and 'cool white' had quite stable and predictable characteristics--in the output curves and the aggregate overall color temperatures and color rendition index for the lamp. This was consistent across brands as well, as certain halophosphate formulations gave the most output per square cm of interior tube space.

 

You are also correct in the spectral composition of LED units. These are doped with a variety of single phosphides and nitrides for 'single' colors (although none of them are true monochromatic), and combinations for "white." Indeed, this is just like the multi-phosphor 'trick' of conventional fluorescent. Google "trichromatic vision" to learn more about how the trick works!!!

 

The only true 'continuous' lighting is incandescent, and gas discharge (not UV/plasma driven) lighting such as HV triggered xenon strobe or tube type (neon, argon, helium, krypton, xenon, etc.) Most of this stuff works great for BW (pan & ortho), once one has worked out the exposure variables. Color not so much so--as was my point in bringing up variables of the old tubes. So consistent that filters could be sold to compensate for the fluorescent color temperature.

 

BTW, most of the figures citing high CRI and "daylight" of 5000-5500Kelvin are sheer BS. The closest any fluorescent tube has ever come has not been the Ott series (close but no cigar) but rather the Philips TL-950--a specialty lamp designed for museum and gallery plus workspace that color matching is important. At one time, I had thousands of parrots around the world living under them... :cool:

Probably worthwhile to become familiar with metering with CFL for those time you want to take photos at a location that uses them. For home use you might like the LED better. Still more expensive than CFL but should last longer. Be aware that CFL and LED lamps may glow a short time after being switched off so be careful when loading film in total darkness.

Be aware that CFL and LED lamps may glow a short time after being switched off so be careful when loading film in total darkness.

 

The same was true of fluorescent fixtures in darkrooms. The typical halophosphate tube was minimally radiant for about 5 minutes--mostly not enough to affect slower emulsuion BW films--but certainly enough to mess up E4 and E6 Ektachrome processing.

 

These small 'tracing' panels sold on Amazon make nice lighting devices. I am using one with Beseler 45mx carriers to digitize MF and LF negatives using the panel as a diffuse background. Watch for flicker and banding though--the reviews will usually indicate if there is an issue. The panels can also be stood up vertically and used as "soft-box" sorts of lighting for tabletop photography. The prices are quite reasonable as well.

 

Cannot state how the color temperature performance is with color negative films or reversal, as I have only used this for negatives in film. Little adjustment for color balance has been required in digital shots.

Still using incandescent lamps in my darkroom for that very reason. I do have a small desk fluorescent as well but don't use it if I plan to load film in a tank. Some of the "afterglow" from fluorescent lamps may be in the ultraviolet region which can still fog faster film. Another caution with fluorescent lamps: be careful if loading film near one of these lamps especially during low humidity as the lamp may light up from static charges.