Potentially useful LEDs for darkroom/alt applications

[Ulophot]

"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..."

I continue to hope for someone to offer a plan/model for hopelessly inept constructors like me to make (or make for us) a simple, white-light LED source for our D2s, etc. at less than "Mercedes" prices. I have allied component costs and they really are fairly reasonable, even at Meanwhile, a question:

Does anyone reading this have an idea of whether the Waveform or other strip lights, used for 4x5 (not 8x10) mounted in, say, a 6.5x6.5inch box (the approx diameter of the D2 diffusion or condenser housing) would equal the illumination of an Aristo or Zone-I coldlight head? That's what I use now, and while a bit more light would be nice, less would not be so great with slow paper/developer combos. Waveform, for instance, lists 450 lumens per linear foot of the 1/2-inch wide strips. I have no idea how that translates and compares.

[Michael R]

Why do you want to replace the existing coldlight?

There are different ways of arranging the LEDs in an enlarger head, which affects the amount of light you have at the negative stage. Also depending on how much you pack in, you might want some type of passive or active cooling. I can think of a few ways of making something relatively simply, but you might also prefer the approach Koraks argued for above - ie some appropriately chosen blue and green LEDs.

[koraks]

I continue to hope for someone to offer a plan/model for hopelessly inept constructors like me to make (or make for us) a simple, white-light LED source for our D2s, etc. at less than "Mercedes" prices.

There's a good chance that this will happen - sooner or later someone with the same enlarger will crack that nut and talk about it. The only problem, as you may have noticed, is the enormous choice of options and specific products. Someone might have a solution, and when you try to replicate it, it turns out the product offering has changed and you have to improvise again. That's just a fact of DIY life...

Does anyone reading this have an idea of whether the Waveform or other strip lights, used for 4x5 (not 8x10) mounted in, say, a 6.5x6.5inch box (the approx diameter of the D2 diffusion or condenser housing) would equal the illumination of an Aristo or Zone-I coldlight head? That's what I use now, and while a bit more light would be nice, less would not be so great with slow paper/developer combos. Waveform, for instance, lists 450 lumens per linear foot of the 1/2-inch wide strips. I have no idea how that translates and compares.

In general, efficiency of leds is way higher than that of traditional light sources, even 'cold light'. So a quick and dirty answer might be: if your current cold light source is for instance rated at 30W, just throw in 30W worth of LEDs and you'll likely have way more light than with the old source. It's kind of a crappy answer, but you need to get into specifics to give a really good answer.
For B&W, as Michael R said, I would recommend not going for white leds but a mixture of green and blue ones. The green ones are not critical in terms of color; they're all pretty similar. For the blue ones, you want royal blue with their emission peak around 450-460nm although lower, between 430 and 450 will likely work just as well. This is pretty much the only caveat when selecting leds for B&W printing. Don't get the regular blue ones as you will be bereft of grade 5, but get ones explicitly sold as 'royal blue' with the appropriate wavelength indicated as well. Most blue led strips (or RGB strips) will NOT give the proper blue light. It'll work fine, but only up to grade 4 or so.
Also, when taking the blue/green route, I would suggest using 2x or even 4x the power for green as you have for blue. There are a few reasons for this, but empirically this kind of ratio seems to give the most flexibility in e.g. equalizing printing times over the entire contrast range. So if you go with strips (and manage to find royal blue ones!), you might put in for instance 1 meter of blue strips and 2 to 4 meters of green strips.

[Michael R]

Ideally blue LEDs for this would be a little lower than 450-460 since most of them emit a little beyond what you want for “maximum” contrast - although honestly how often does one really need grade 5? On the other hand for some reason I’ve seen this complaint relatively often.

Waveform blue peaks at 460nm if I remember correctly. I’m sure there are other options, probably cheaper also.

If one were really concerned with getting maximum contrast Waveform has a violet strip peaking at 415nm. Of course paper sensitivity is a variable when it comes to grade spacing and speed. I’m not actually suggesting adding violet LEDs. In the rare case you can’t get enough contrast from the blue LEDs you could resort to a sharp cutting filter in the light path to attenuate longer wavelengths emitted by the blue LEDs. Or just intensify or dupe the negative.

Anyhow, my diversion aside, this can certainly be done without going too far down ratholes or spending a fortune.

[koraks]

Re: the blue led wavelength: the usual wavelength is/was indeed something like 470nm or so, but these days, you can get pretty much any hue ranging from 365nm (UV) all the way down to IR in narrow spacings. So for blue leds, take your pick; you can get 460, 450, 440, 430, 420...etc.
I settled for royal blue because it also works well with color RA4 paper as part of an RGB array. RA4 is of course far more critical in terms of light source selection. For B&W it doesn't matter all that much, just don't pick a blue led that has too long a wavelength (too close to green) as that impacts the highest achievable grade.
Also note that there's no benefit in choosing a lower wavelength with the idea that it may somehow unlock even higher grades in the paper that are otherwise unachievable. This is not the case; the highest contrast grade is always paper-limited and there will be no meaningful difference between say 430nm and 450nm leds in terms of paper grade.
There is, however, quite likely a significant downside to selecting leds that are too close to UV (so e.g. 430nm and lower) as this will most likely activate also the low contrast layer(s), effectively reducing contrast. So the royal blue 'peak' is a pretty sensible compromise.

[Michael R]

Quite right. You're not going to get a magical grade 5+ using shorter wavelength LEDs. The issue with the longer blue wavelengths isn't a matter of peak but simply that the emission band extends too far toward green.

In any case, someone ought to start a lower cost (relatively) LED head business

[Ulophot]

Glad for the responses, though there's not much I can do with them directly. Again, for the record, I am not one who could construct such a thing.

RE: Why replace the coldlight: My original Zone VI died. I found another about three years ago at a thrift store. It works okay, but life for lamps and the rest of the stuff in the head (sorry for the advanced technical terminology) is undoubtedly increasingly borrowed. The lamp flashes dimly after exposure, not enough to be a problem in printing, but surely an indication that something is dying. A new lamp from from Aristo is $180 plus shipping, and I can't even get the head cover off, let alone know how to replaced the very delicate lamp without breaking it. Nor do I solder. I have what was to be a back up unit, but it buzzes loudly and the lamp broke in shipping. I'm out of my league trying to repair such things. LED is the future.

I'm happy to continue using my Ilford filters under the lens. I would thing economy and simplicity of design would indicate white LEDs, which, all being the same, would not require extra (whatever that would be) diffusion to blend blue and green.
RE: koraks's 3 meters of LED strips ("you might put in for instance 1 meter of blue strips and 2 to 4 meters of green strips. ")-- I don't know how that is being imagined in a 6.6x6.5" box.

[Michael R]

Diffusion is just for uniformity of any light (and depending on how you construct the box you might not even need supplemental diffusion). You don’t need to mix the blue and green as long as they each light the negative stage uniformly. You can then expose them together or in succession.

Remember the paper doesn’t see mixed colour. Only our eyes/brains do that. The paper just sees whatever wavelengths of radiation the individual LEDs emit.

Think of it this way. Suppose you had an enlarger head filled with two types of LEDs. One type emits a single 450nm wavelength which we see as blue. The other type emits a single 550nm wavelength which we see as green. Assume there are enough of each type, and some diffusing material above the negative so that either the green or blue LEDs can evenly illuminate the negative. Now suppose you turn them both on. You would see some cyan type of colour, an additive mixture of blue and green. But the paper does not see cyan. It sees just the blue and the green. The two wavelengths do not actually mix to produce an intermediate wavelength. The mixed colour is a purely psychophysical phenomenon.

This is why it dos not matter to the paper whether we make one exposure using a mixture of green and blue, or a green exposure followed by a blue exposure.

The same thing applies when VC filters are used under white light, except that the process is subtractive. The light we see as white includes many wavelengths. The paper sees the various blue and green wavelengths in white light. When you put the VC filters in the light path all you are doing from the paper’s perspective is varying the relative proportions of blue and green wavelengths that get through.

[andreios]

Guys, this whole thread makes me feel very inadequate. I think I would be able to make such a thing - got some practice with soldering kitchen LED strips as well as some basic RC model stuff for the kids, but I would echo Philips' (Ulophot's) hope for someone putting together a somewhat foolproof how-to or a chart what is needed and how to put it together...
I use a Durst 138, all the bulbs that I have are not big enough to illuminate 13x18cm negatives so I have to help them with diffusion and would really like to change the light source for something more energy efficient than the 300w or 500w bulb...

[Tin Can]

It is hard as LED are constantly evolving

Usage still requires big $$$ for Heiland or personal experimentation

Many are experimenting, I hid in our DIY section for years, experimenting, condemnation is not fun

Most here are amateurs of varying expertise, we don't make money, we spend it for our love of the hobby

Some dominate by absolute declarations of perfection we never see

Never helpful

Today I am searching eBay for what I need, they now sell darn near anything

Then I compare and contrast with Amazon

Industry doesn't help, they want volume sales

Blue and Green light separately