Building a Darkroom: loads of Q's

[koraks]

Led strips these days also come in CRI > 95 variants, also CT (warm + cool white which can then be mixed according to your desire). These are quite alright for anything except the most critical color work. For me they're good enough also for color printing.

cleaning

You mentioned it...might be worthwhile to think about how you'll clean things. For instance, a coarse concrete floor will be a nightmare; it'll always be a dust bowl. A room with lots of nooks and crannies and open-shelf storage space takes ages to clean, so odds are you won't do it (regularly). It helps to think not only about use, but also maintenance - how will you keep your space tidy and clean? And yes, your prints WILL be better for it.

 

[ragazzo]

To everyone who has already offered so much....I can't express my gratitude enough. I'm going to take the time to respond to everything but just wanted to update to say I'm enthralled by all the help.

 

[MattKing]

On the cleaning point, and in the realm of after winning the lottery, I've always wanted a darkroom floor with a floor drain and a rubberized floor covering material that extends up over the rounded join with the walls and a few inches up the wall as well.
Mop away!

 

[Sirius Glass]

On the cleaning point, and in the realm of after winning the lottery, I've always wanted a darkroom floor with a floor drain and a rubberized floor covering material that extends up over the rounded join with the walls and a few inches up the wall as well.
Mop away!

That would be a good start but my goal is a self cleaning darkroom. Also while I am at it self cleaning kitchens and bathrooms would go on the list of must have features.

 

[Mr Bill]

Regarding fluorescent lamps... there are actually some very good specialty lamps for dealing with color. But... the general-purpose fluorescent lamps found in most stores today are what I would call eco-friendly or energy-efficient. (They have a high lumen output per watt.) These lamps are very bad for critical color viewing. Also, high CRI is no longer a good screening test for such fluorescent lamps - the manufacturers know how to "game" the test. Such an eco-friendly lamp puts the spectral output in places where the human eye is most sensitive and perhaps at the test zones for CRI. So it may look good on paper yet be horrible for critical color work.

Fwiw LEDS have a slightly similar situation with respect to CRI. They may have a fairly high CRI rating, but if one looks at a more complete breakdown - CRI rating by individual test color - one typically see that a couple of the test colors have miserably low CRI ratings. The rest are very high (good) so the overall rating looks pretty good. One should be aware of this weakness in the ratings. I would suggest a reality check by also viewing prints under outdoor lighting, just to make sure your viewing lamps are not misleading you.

 

[Sirius Glass]

Florescent lights need to be have cool light, i.e daylight, for one to see color prints or tinted black & white to see the colors correctly. Also florescent lights can glow for a short time after they are turned off, taking even longer is the room is cold, and that can work against one in the darkroom.

 

[AgX]

I would suggest a reality check by also viewing prints under outdoor lighting, just to make sure your viewing lamps are not misleading you.

Or testing the LED lamps at a colour chart against an incandescent lamp, which may be filtered for colour temperature if necessary.

 

[Mr Bill]

Or testing the LED lamps at a colour chart against an incandescent lamp, which may be filtered for colour temperature if necessary.

That's true, but there's a further issue that can happen with actual photo images. Color test charts tend to be well-behaved spectrally whereas an actual image has various combinations of the dyes/colorants. So there could be some insidious, if that's the proper word, interactions between light and image.

Rather than try to explain the technicalities I'll tell the tedious story. We printed like zillions of nominal 8x10 inch "units" on RA-4 paper. They're hand corrected in "color booths" based on initial test strips. ...Skipping lots of details.... At some point the company started doing some inkjet products in sizes we don't have in RA-4, and they also do the entire portrait session likewise so that all prints match.

One of the execs in the "production" areas calls me. Bill, we got a big problem here... what's going on? They've been doing inkjet color correction same as the RA-4. All looks OK, until... someone had some inkjet prints near an outside window and noticed... the color changed, for the worse. It's not good enough quality to ship, and all has to be reprinted. The first question is, what light to color balance under? The second question is, what's wrong with the color booth lighting? It still works fine with RA-4 prints.

The obvious assumption is that the lighting in the color booths has changed, but... they have been maintaining an inspection program for many years. Each month every color booth in the building is checked with a Minolta colorimeter, recording the color temperature and "brightness" (whatever the units were). They all conform to a booth spec set many years earlier which includes lamp specs (mftr and part #) as well as a manufacturer spec'd CRI (color rendering index) which ought to be high enough. They checked, and found that the proper lamps are in use. And... the system continues to work fine with RA-4 prints directly from film.

I'm going to continue in another post in case anyone wants to ponder the mystery.

I'll add two more bits... 1) I did observe the color changes myself. I can hold two well-balanced prints in the color booth - one on RA-4 paper, the other inkjet. When I go near an outside window the RA-4 print stays fine, but the inkjet print visually changes such that it's not an acceptable product (by our guidelines, a nominal 5CC outer limit). 2) the original color booth specs were set by a well-qualified guy, with an RIT photo science degree (also a good friend, passed away way too young).

<cont>

 

[wiltw]

That's true, but there's a further issue that can happen with actual photo images. Color test charts tend to be well-behaved spectrally whereas an actual image has various combinations of the dyes/colorants. So there could be some insidious, if that's the proper word, interactions between light and image.
...I'm going to continue in another post in case anyone wants to ponder the mystery.

I'll add two more bits... 1) I did observe the color changes myself. I can hold two well-balanced prints in the color booth - one on RA-4 paper, the other inkjet. When I go near an outside window the RA-4 print stays fine, but the inkjet print visually changes such that it's not an acceptable product (by our guidelines, a nominal 5CC outer limit). 2) the original color booth specs were set by a well-qualified guy, with an RIT photo science degree (also a good friend, passed away way too young).

<cont>

My assement of what happened:
Illuminant metamerism...an occurance especially with inkjet prints...inkjet prints are best viewed using 5000K lighting for color accuracy.

 

[koraks]

In with @wiltw.

Fwiw LEDS have a slightly similar situation with respect to CRI

That's true, even high CRI leds aren't perfect or anywhere near it. For some leds, spectral charts are published; compare those to sunlight or daylight-balanced tungsten and the differences become very apparent. But I just don't want to install tungsten in my darkroom anymore; it's way too hot at the light levels I need, and we use enough energy as it is in our household.

 

[Mr Bill]

<cont from post 33>
Regarding print viewing lamps...

So, I went to check out the color booth lighting myself, but I'm gonna use a spectrophotometer (to see if anything is wacky, spectrally). The instrument can also calculate CRI and color temperature from the spectral readings.

Surprise! The lamps (same part#) that were once fine now have a much lower CRI, down in the 80s (ideal is 100), although the color temperature remains the same. The spectral output is "spiky," in the manner of an eco-friendly lamp, and in fact this particular model lamp has now become an eco-friendly energy-efficient lamp. Strangely, no one in the company had noticed, although they think they have everything nailed down with their regular monitoring, changing out lamps on a schedule, etc.

So the actual lamp is the source of the problem, even though it still works OK with RA-4 prints.

Illuminant metamerism...an occurance especially with inkjet prints..

Exactly. (You have to get up pretty early in the morning to get one up on wiltw.)

At this time I was no longer involved in those aspects of the business so don't know exactly how they resolved the color booth issue. (They had tech contacts inside of Kodak, Konica and Fuji, so I'm sure it worked out. )

Anyway, this experience is one of the reasons why I recommend that people use outdoor light as a reality check on their color viewing lamps.

Regarding why inkjets are more sensitive I had a discussion with a guy from Kodak not too long after that. (They had a new inkjet paper system and he was here to setup one of the Epson printers in our R&D lab with custom firmware to handle it, etc. He's a color guy from KRL, so knows his way around.) Inkjets are fairly well known to have the capability of more saturated colors than an RA-4 paper; he pointed out that this is done by making the colorants with narrower spectral dye peaks. And consequently these narrower peaks make the print more sensitive to the light source. RA-4 papers, on the other hand, have broader dye peaks and are thus less sensitive to the viewing light source.

To be relevant in this thread there ought to be a recommendation for color print viewing. I would think that a modern LED might be pretty good. But ideally it would have a minimal spectral dip between the blue and green range. I would look at this rather than the CRI. I'm guessing they're more expensive.

Regarding color temperature, wiltw suggests 5000k. Fwiw this is a graphic arts standard. Personally I think a lower color temperature may be better for general use. We used to use something like 4200K as a compromise between incandescent (~2800K), the common home light of the day, and photographic daylight (~5500K). I'm not sure what would be best today. But one can always bias the print color away from the viewing light color if they want. So, maybe not that important as long as you have a good reference print to compare against.

 

[AgX]

Anyway, this experience is one of the reasons why I recommend that people use outdoor light as a reality check on their color viewing lamps.

Fluorescent lamps were often used at color-checken booths. That is why I advised instead an incandescent lamp as it got a continuous spectrum. Its colour temperature can rather easily be checked an adapted by filters. This yields the advantage of being weather amd daytime independent at checking. I do not see the chance for effects you experienced at your booths.