Gast
Hello!
I thought I’d share a tip based on my experience with my new darkroom lamp.
So, I bought a third brake light with LEDs (from around €15) and a cheap plug-in power supply (9V, approx. 100mA), connected the two wires using terminal blocks, set it up in the darkroom, and since then I’ve had ‘daylight’ brightness throughout the darkroom. It’s never been this bright in there before; I’m really impressed. Any coin tests etc. haven’t caused any changes to the paper so far, so the paper is probably really ‘dead’ to this wavelength. :-).
And all this at 9V, compared to the 12V normally needed for the rear light...
Just how bright would it be at 12V then?
;-)
So, I’d be interested to hear what you think of it.
Philip
Gast
I use one of those battery-powered LED bike rear lights as a 'DuKa torch' – very handy if something falls down, or for checking the exact snatch point when lith printing...
Gast
...so,
I’ve got one of those LED string lights that you plug straight into a socket.
Standard 230V screw-in base (E14 or thereabouts).
It gives off a lovely red light, but it shouldn’t shine directly onto the work area – because of fogging and all that.
It costs 9 euros at Conrad – no DIY required!
Size
Matthias
MirkoBoeddecker
Phillip,
Have you tested our paper with it as well, or just Agfa, Ilford and Kodak?
Best regards,
Mirko
Renate
Unfortunately, red LEDs are not always as red as they appear to the human eye. Firstly, there are various red LEDs on the market, each with a slightly different spectral peak. Secondly, the LEDs are not monochromatic. This means that, in addition to the peak, there is also an infrared and an orange component. You can only see this if you use a spectroscope or apply a veil to the images. Even the red Plexiglas cover did not sufficiently block the orange component in my brake light. So I added a dark red filter. The veiling test with ADOX paper then proved positive. The light is wonderfully bright. I only use LEDs that have their peak at a wavelength of 635 nm or longer.
With Agfa and Ilford paper, you don’t need to be so fussy; even a strong orange doesn’t cause fogging. However, I don’t like the results with these types of paper.
LEDs with other colours are even less monochromatic. Yellow LEDs with a peak at 590 nm are only suitable for colour enlargements if you use additional filters to suppress the green and orange components and significantly reduce the brightness.
Gast
Hi Mirko (and everyone else),
I once accidentally shone a similar (homemade lamp) directly onto a piece of Polywarmton for a few seconds (about 10) before it was laminated.
You could then see each diode individually as a shadow. Never had any problems otherwise.
It just depends on the diodes; the longer the wavelength (more nm), the better. In my opinion, the variation in design is not a critical factor with paper. (Or frequency noise, for that matter).
Diodes are, by their very nature, monochromatic (okay, with some noise) and not white light with a finite, steep filter.
But with enough force (see above), paper can probably be scorched with a hot iron before it glows red.
Regards
Martin
Renate
Hello,
There are many myths about light-emitting diodes, and one of them is that they are monochromatic. That is definitely not true, as I have already explained in detail in my post above. Anyone who doesn’t believe this should get hold of a spectrograph and take a close look at the light emitted by light-emitting diodes. The eye is very easily deceived. That is why a veiling test is always necessary, particularly with light-emitting diodes.
Best regards,
Renate
cfb_de
Hello Renate,
You can do this without a spectroscope, just using a datasheet :-)
Here, for example, on page 4, you can clearly see what the spectrum of a red LED looks like and what the specification of the ‘spectral half-width’ – which is included in the product specifications for good reason – actually means.
Due to the way they work (excitation of electrons to higher energy levels), LEDs *cannot* emit monochromatic light, as the occupation of the energy levels is, on the one hand, statistically distributed and, on the other hand, the excitation unfortunately also depends on temperature (actually a consequence of the statistical distribution, which is temperature-dependent). Hence the half-width, which means that although an LED has a dominant wavelength, it also emits radiation above and below it. With a spectral half-width of 10–40 nm, I would no longer refer to it as ‘monochromatic’.
Best regards,
Franz
Renate
Hello Franz,
You don’t need to explain that to me. I’m a physicist and, on top of that, very familiar with electronics. Of course, I know that data sheets exist and I’ve looked at them carefully. But they’re of no help to the average amateur photographer.
Nor do I need a MAN to back up my posts with theoretical arguments. What’s more, your explanations aren’t physically correct. But that’s irrelevant when it comes to taking good photos and has no place in this forum.
Renate
cfb_de
Hello Renate,
Why the snarky reaction? It was clear from your first post, if not before, that you’re an expert in the field. And as a chemist, I’m no match for you when it comes to semiconductors, either.
My intention was quite simply this: presenting the basics to the average reader here, yet still ‘claiming’ (since you didn’t explain it) that popular belief is a fairy tale (which it undoubtedly is), does little to win over the average reader, who doesn’t believe everything they read in forums anyway.
That is why I tried to clarify a few things quite simply: 1): You can *see* this as a small image in the datasheet without any knowledge of the basics. The datasheet comes from the manufacturer, who, unlike us here in forums, can be held *accountable*. 2): It does in fact have a scientific, explainable basis. Since I haven’t gone and written a full-length treatise on the Bädemodell, atomic and orbital theory, etc., that’s probably forgivable simply because we’re not in a lecture theatre here and the majority of readers can’t or won’t understand it anyway.
If necessary, I’ll be happy to provide that later and prove to you that I’m no dunce when it comes to physical chemistry.
Is everything back on track? The question of man or woman and who needs whom and when is, in fact, irrelevant. What is certain is that both women and men can make for both good and bad scientists.
<duck>It is also clear, however, that women should leave the cooking to those who can do it and are therefore, for the most part, replaceable in the kitchen by a Miele appliance.</duck>
In my next reply to one of your posts, I will put what I’ve learnt into practice and take it into account. But for now, I’m off to the kitchen. My girlfriend is hungry.
Best regards,
Franz
heinrich
Hello,
I’m currently toying with the idea of lighting my darkroom with LEDs. At what wavelength and spectral half-width does it start to become worthwhile? As far as I understand, I don’t need to worry too much with Agfa paper, but what about Polywarmton?
To the engineers and physicists among you:
In theory, LEDs should be perfect for creating a wonderful multi-level lighting setup for split-tone printing. Green for the soft-working emulsion and blue for the hard-working emulsion. What’s missing is the control system; perhaps someone on this forum has a feasible idea and would be willing to share it.
Best regards,
Heinrich
Gast
Wow....
I had no idea you could turn this into such a science!
For me, the only thing that really matters is that there’s enough light without any fogging.
With the papers I’ve used so far, everything’s fine.
These were:
Agfa, Ilford, Tetenal, Wephota, Forte, Amaloco – some of them on baryta paper, most on PE...... yes, I think that’s it.
In my opinion, it’s important to dim the light just enough so that you can still see properly.
That way, nothing really can go wrong.
Matthias
Gast
Hello everyone,
I find it quite remarkable just how much ingenuity is on display here. :o I just can’t quite wrap my head around it. I can get second-hand ‘genuine’ DuKa bulbs on eBay for practically nothing if you go for the basic models, and even the more expensive versions like the Kindermann Dukalux SL Tandem are very cheap. Just two weeks ago, I picked up one that was as good as new for €39.
Renate
I’ve also considered using LEDs for a multigrade light or even as a colour head. However, I ruled it out because the LEDs don’t achieve sufficient sharpness in separating the colours. Green LEDs have a noticeable blue component, and blue LEDs have a green component. It probably won’t work without additional filters. Furthermore, it will be difficult to achieve sufficient brightness. The light from the LEDs only appears so bright because it is emitted at a narrow angle. For an enlarger, however, the light needs to be diffused over a larger area. You would need quite a few LEDs to avoid having to undergo extensive exposure for hours on end. Furthermore, as with incandescent bulbs, a large proportion of the electrical energy is converted into heat in LEDs. Effective cooling is therefore essential. Furthermore, the brightness of LEDs diminishes with use. This means the exposure would have to be recalibrated at regular intervals.
I therefore stick to the classic method with a colour head and a 100 W halogen lamp. Testing a new paper takes about two days. After that, I can achieve the desired results very quickly and precisely.
Regards, Renate
P.S. I’m used to being called bitchy from time to time, and it doesn’t bother me. The word is always used when men run out of factual arguments. Thank goodness not all men are like that, and discussing photography with most of the men here is fun.
Gast
I’ve no idea where Renate manages to get hold of “shares” in LEDs (monochromatic), but
for Heinrich:
I’ve given this a go:
Durst 138 (plenty of space for tinkering)
1x 5W Lumiled royal blue
4x 5W Lumiled green
Current regulator from eBay, switched via banana plug.
The royal blue one is brilliant; I won’t use anything else for lith printing anymore. As a quasi-point light source, it’s also incredibly sharp.
The 4 green ones around it make the papers I tested (Polykalt and Polywarm) appear roughly 4–5 stops darker than the single blue one.
I admit, as I still haven’t ordered a Stouffer, I haven’t been able to measure how much blue I can mix in (to gain speed) before leaving the gradient at 00 in the direction of hard.
Before that, proper control is pointless anyway. Otherwise, there’s a bloke from England who’s posted a complete build plan with a microcontroller online for this. He managed the green as well, though he built it with multiple diodes for a diffuse effect rather than a single point.
@Renate. If you think the diodes’ frequencies don’t align exactly with the primary colours, you might be right. The colour components in the paper do react rather broadly (meaning you also get red and blue exposure when you shine a monochromatic green light on it).
Regards
Martin
Gast
P.S.: Just as a rough guide:
The 5W royal blue lamp is about 2 f-stops brighter than the 300W opal lamp. The 4x5W green lamp is 2–3 f-stops dimmer.
And since when does the light in an enlarger ‘have to be diffused’??????
heinrich
Hello Renate,
A small amount of blue in green LEDs shouldn’t really be a problem as long as it’s small enough. The same applies to the blue component in green LEDs. Here, one would need to look at the spectral energy distribution of the LEDs in comparison with the spectral sensitivity of multigrade papers. When I look at my Multigrade filters – thin, coloured plastic – they can’t be up to much in terms of the spectral purity requirements for the respective light colour.
The fact that one LED per colour isn’t enough doesn’t bother me either, as I’m a fan of diffuse illumination for my negatives. So you just use several (I was thinking of a 15×15 array, or something like that). And as for LEDs ageing, well, my two 300-watt halogen lamps in my Durst Laborator 138 do that too, which also means that the gradients shift slightly over time.
So what’s the argument against such a project?
In my view, only the effort involved in the development of the control system; I’m a biologist, not an electrical engineer. I can operate a multimeter and tell a low-pass filter from a high-pass filter, but that’s about it.
@Max: Do you still have the Englishman’s web address?
A quick note on diffuse illumination:
With the condenser light on my now-mothballed Durst DA900, the highlights always ran away from me (which is why I’m now using the 138 with a colour head); I couldn’t – and didn’t want to – develop my negatives that were flat. Zone 9 only set itself to a gradient of 2.5 with N-2 development. Hence my preference for diffuse illumination. Regarding the Stouffer, is that a densitometer?
Regards
Heinz
fotohuisrovo
Heiland now offers a cold light source featuring LEDs and a split grade. It also incorporates red LEDs so that you can check the exposure on photographic paper. Prices start at €1,400.00
Best regards,
Robert
Renate
Hello,
The only thing holding me back from this project is that I’d be investing a lot of development time in a project with an uncertain outcome. My current solution, using a halogen lamp and a colour head, gives me excellent results. The LED solution might be just as good, but it will never be better and, in all likelihood, will actually be worse. I’d rather spend my limited free time taking photos and enlarging them.
Regards, Renate
To Max,
Take a look at an LED with a spectrograph and you’ll see what I mean by ‘spectral components’. There is NOTHING monochromatic about it. But I’ve already described that in detail above. Alternatively, you could also have a look at an LED datasheet.
