Potentially useful LEDs for darkroom/alt applications

[Tin Can]

My scheme to mount multi Everclear has evolved

I now have 2 SS folding shelf brackets, adding crosswise supports

They will fold away to wall

Black OR white TBD Coroplast folded will block stray rays as necessary

or perhaps just leave DR using timers

Winter work

I have one of the 100w Everbeam's for 8x10 and it works well for Salt (and presumably other alt processes). Earlier in the year I purchased 8 of the 24" Barrina 395nm 9w T5 LEDs but the single Everbeam gives much shorter exposures.

How are you going to mount yours? I'm thinking of picking up at least 1 (possibly more) for larger negatives.

[Michael R]

Nice. Those Waveform Absolute realUV strips look pretty cool (and available in 365nm), but looks to be more expensive than the Everbeam's. Visiting their web page, how many feet did you use for your light box?

Hi Carl, I wound the entire 16.4’ reel into the box. It fit nicely into 15cmx10cmx14cm. 1.5:1 was the aspect ratio I wanted for this box - it is for my sensitometer build which is why I went overkill with the Absolute strip. I really wanted the most continuous, high Re (not just Ra) spectrum.

Winding the strip around the perimeter of the box makes the whole thing function as a mixing chamber, and will require virtually no, or minimal diffusion (didn’t put the front/bottom on yet as you can see). Reduced diffusion requirements mean less light loss. This unit puts out approximately 6000 lumens.

I’m thinking I can likely scale this up a little to make an excellent 4x5 enlarger light source. Another option would be to use their tungsten strip or sheet. Those are not quite as good as the Absolute series but still excellent and plenty good enough for enlarging, likely much higher real CRI than any LED heads you buy off the shelf. The FilmGrade strips put out even more light than the Absolute strips, and a tungsten balance should work quite well with Ilford Multigrade filters.

A nice thing about their stuff being geared toward the video/film industry is there is almost no flicker in the system, and the PWM dimmer functions at 25kHz (they test up to 240fps video). This is all overkill for enlarging/printing of course, but is important for sensitometry, which was the original purpose of my project.

Sorry if this seems like marketing. I’m not affiliated at all with this company. Just a satisfied customer who needed something good but also plug-and-play/trivial to hook up (I’m not an electrician).

[koraks]

I’m thinking I can likely scale this up a little to make an excellent 4x5 enlarger light source. Another option would be to use their tungsten strip or sheet. Those are not quite as good as the Absolute series but still excellent and plenty good enough for enlarging, likely much higher real CRI than any LED heads you buy off the shelf. The FilmGrade strips put out even more light than the Absolute strips, and a tungsten balance should work quite well with Ilford Multigrade filters.

High CRI isn't really necessary for an enlarger light source. It even isn't for color, and for B&W it's entirely superfluous. It doesn't hurt either, of course, but it's just not a relevant consideration.

[Michael R]

High CRI isn't really necessary for an enlarger light source. It even isn't for color, and for B&W it's entirely superfluous. It doesn't hurt either, of course, but it's just not a relevant consideration.

I’d rather have a high CRI/smoother spectrum for sensitometry. Low flicker is necessary.

For enlarging/printing, the higher the “complete” CRI, the closer the approximation will be to whatever incandescent source, so even for black and white I would not go as far as calling it superfluous. Of course it isn’t necessary but for example if one is accustomed to using an incandescent source with VC filters things will be more wonky with typical garbage “white” LEDs.

Could also help to have a high CRI for digitizing film with digital cameras, as seems to be a trend.

Anyway I’m not trying to sell anyone anything. I was just happy to find some decent quality/violet emission LED plug-play systems with good photometric specs, low voltage drop and low flicker.

[koraks]

I’d rather have a high CRI/smoother spectrum for sensitometry. Low flicker is necessary.

For enlarging/printing, the higher the “complete” CRI, the closer the approximation will be to whatever incandescent source, so even for black and white I would not go as far as calling it superfluous. Of course it isn’t necessary but for example if one is accustomed to using an incandescent source with VC filters things will be more wonky with typical garbage “white” LEDs.

Could also help to have a high CRI for digitizing film with digital cameras, as seems to be a trend.

In all the applications you mention, you need to ask yourself to what extent the availability of a continuous spectrum is in fact beneficial. The comparison with incandescent bulbs is tricky and I'd say misleading - the question is not how well the new technology matches the old one. The question is to what extent the new technology matches the demands of the job.

Black and white paper? It's all sensitive to blue and/or green. There's no benefit whatsoever in having a continuous spectrum. In fact, for split grade printing, a continuous spectrum is more of a liability than an asset - albeit with minor impact. Appropriately chosen blue and green leds are by far the most efficient and effective approach conceivable with today's technology.

Color paper? All optimized for narrow band RGB semiconductor light sources these days.

Digital cameras? Again, RGB. Although I admit just throwing a high CRI light source at the job is a straightforward solution with little hassle.

Sensitometry? We can debate this one, because it's out in the open how you implement the actual sensor front end. But here as well, with today's technology, you'd always be working with a compound signal of fairly narrow-band wavelengths if you want any kind of decent channel separation.

In all cases above, CRI is far less interesting than a proper match between the light source and the application. In photography, interestingly, only in the recording stage CRI is important. THAT's where it's absolutely vital, as well as in judging prints. CRI matters, a lot. Just in different areas!

[Michael R]

Of course you don't need a continuous spectrum to expose blue/green sensitive paper. But if you are using say Ilford MG filters and have light with violet-blue-green components more similar to a tungsten source, you're more likely to get closer to Ilford's specs for grade spacing and speed matching. Nothing mandatory here, but it's not simply a case of matching the old technology for its own sake.

I disagree that it is a liability vs blue and green LEDs, or RGB LEDs. White light is less efficient in principle, however in practice "appropriately chosen blue and green LEDs", or RGB LEDs doesn't happen. It could of course happen, but nobody does that properly. Then they complain. For anyone else interested, CRI is only one measure, and it can be misleading without detail/context.

I understand the physics. I'm sure you understand it. Perhaps I didn't explain myself well. I wanted specific characteristics for my sensitometer light source, and it occurred to me that high CRI LEDs might make for simpler LED implementations for things like enlarger heads and such. That's all.

In all the applications you mention, you need to ask yourself to what extent the availability of a continuous spectrum is in fact beneficial. The comparison with incandescent bulbs is tricky and I'd say misleading - the question is not how well the new technology matches the old one. The question is to what extent the new technology matches the demands of the job.

Black and white paper? It's all sensitive to blue and/or green. There's no benefit whatsoever in having a continuous spectrum. In fact, for split grade printing, a continuous spectrum is more of a liability than an asset - albeit with minor impact. Appropriately chosen blue and green leds are by far the most efficient and effective approach conceivable with today's technology.

Color paper? All optimized for narrow band RGB semiconductor light sources these days.

Digital cameras? Again, RGB. Although I admit just throwing a high CRI light source at the job is a straightforward solution with little hassle.

Sensitometry? We can debate this one, because it's out in the open how you implement the actual sensor front end. But here as well, with today's technology, you'd always be working with a compound signal of fairly narrow-band wavelengths if you want any kind of decent channel separation.

In all cases above, CRI is far less interesting than a proper match between the light source and the application. In photography, interestingly, only in the recording stage CRI is important. THAT's where it's absolutely vital, as well as in judging prints. CRI matters, a lot. Just in different areas!

[koraks]

Well, nothing wrong with using high CRI leds for the purposes you mention. It's one way of getting there. I must vehemently disagree on the notion that appropriately chosen blue/green or RGB leds doesn't happen. Especially for B&W, it's relatively easy to get there DIY-ing your way into it with some basic knowledge. For color it can be done as well. Heiland seems to do a pretty neat job at it, at least. I think I do, too, without any commercial interest or ambition.

I guess I just want to give a counterbalance to the sentiment that high CRI is the only or even the best way to go. There are several ways to skin this cat.

Btw, I have some fairly high CRI led strips on order for my new darkroom. Seems like low-cost Chinese sellers are starting to service this niche as well, which make sense. Today, we tend to call >95 high CRI (or even >90...); I bet that >95 will be default in 2-3 years and high will be >98. Today's special is tomorrow's fodder.

[Michael R]

I mostly agree, Koraks - except regarding appropriately chosen blue/green or RGB LEDs, although my disagreement is not vehement . Since I know you understand light and emulsion sensitivity, I have no doubt it was relatively trivial for you to DIY it. Probably Heiland also - though a little expensive for what it is (just my opinion, even though it comes with the split grade bla bla).

However anecdotally when the average DIY person makes a blue/green or RGB head they seem to frequently have problems with things like contrast range and spacing, because they just buy whatever blue or green etc. LEDs. At least this has been my experience having read many threads over the years on forums. Therefore I still think for DIY LED conversions it would likely be simpler for many people to go with relatively high quality/CRI/Re white light even though bypassing filtration with “additive” mixing/successive exposures is certainly a more ideal end game as you rightly point out.

I think you’re probably right about the higher CRI and higher R9/Re LEDs (ie violet emission/excitation with RGB phosphors) rather than the traditional blue emission with yellow) making their way into cheaper stuff. Hopefully the same for flicker control and higher PWM dimming frequency, not that these matter for print exposure.

The “Absolute” strip I went with for my DIY is obviously overkill, and of course I won’t get exactly the output spectrum in the end anyway because of the mixing box, but I’m quite pleased with how it worked out.

Well, nothing wrong with using high CRI leds for the purposes you mention. It's one way of getting there. I must vehemently disagree on the notion that appropriately chosen blue/green or RGB leds doesn't happen. Especially for B&W, it's relatively easy to get there DIY-ing your way into it with some basic knowledge. For color it can be done as well. Heiland seems to do a pretty neat job at it, at least. I think I do, too, without any commercial interest or ambition.

I guess I just want to give a counterbalance to the sentiment that high CRI is the only or even the best way to go. There are several ways to skin this cat.

Btw, I have some fairly high CRI led strips on order for my new darkroom. Seems like low-cost Chinese sellers are starting to service this niche as well, which make sense. Today, we tend to call >95 high CRI (or even >90...); I bet that >95 will be default in 2-3 years and high will be >98. Today's special is tomorrow's fodder.

[bob carnie]

I have gone a bit further down the wormhole due to MR who are the experts in Nuarcs telling me they would not send in a technician to my lab because my 32 1Ks unit was built in 1994 and they are not servicing my unit or supplying parts. I have a electrical dude coming in and may have him look inside and decide what the issue is with my unit, I think it may be a ballast but what the hell do I know. I just print . So I have spoken with this Detroit Michigan company http://www.douthittcorp.com/ and they were extremely helpful and have refurbished units with light ballast and integrator shut off and on unit and send out a lot of power. They are not cheap but I do a lot of printing and with a hanging 1 ks system trying to do 30 x 40 inch gum over pd I am in 20 min per layer timelines which is 4 times what I am use to doing 16 x 20 so its a real solution, I just have to pick a few more brains here and on FB alt groups before I decide to go this route.

[Ron McElroy]

I have one of the 100w Everbeam's for 8x10 and it works well for Salt (and presumably other alt processes). Earlier in the year I purchased 8 of the 24" Barrina 395nm 9w T5 LEDs but the single Everbeam gives much shorter exposures.

How are you going to mount yours? I'm thinking of picking up at least 1 (possibly more) for larger negatives.

I haven't had an opportunity to work up anything yet.