Duka lamp

erwin · 2006-11-14T16:03:51+00:00

Hallo, ich habe eine Frage zu Color-Dunkelkammer-Lampen. Und zwar: Im Fach-Handel sind Natriumdampflampen erhältlich (z.B. Kaiser Duka 50). Diese sind je...

erwin

Hello, I have a question about colour darkroom lamps. Specifically: Sodium vapour lamps are available from specialist retailers (e.g. Kaiser Duka 50). However, these are very expensive. So my question is: Can you also use the vapour lamps available in electrical shops? If so, which ones would you recommend? Thank you for your reply Kind regards Justus F.

Richard

Hello Erwin / Justus, Without knowing the lamps you’ve mentioned, I’ll put it simply: definitely not! Sodium vapour lamps from electrical retailers are presumably intended for general lighting purposes. As the light isn’t particularly pleasant and, above all, allows for good contrast vision, it’s a classic outdoor light. If you now compare the light output required there with that of a Duka lamp, you should realise for yourself that a street lamp in the Duka cannot be desirable. Visible light always exposes photosensitive material; whether it causes interference is a question of intensity, duration of exposure and sensitivity to the relevant spectral range. If it’s a question of cost... Do you really need a colour light? Might LEDs be an alternative? Regards Richard

cfb_de

Hello Justus, The fact is that photography actually applies simple principles of physical chemistry. This is the case, for example, with light sensitivity, as well as with temperature and concentration dependencies during development. With regard to light sensitivity, a derivative of the photoelectric effect is utilised. Namely, the fact that only radiation of a specific wavelength (‘light colour’) interacts with matter (‘photographic paper’). Unfortunately, our beloved atoms behave like small children: they know this, but they don’t always stick to it. The proportion of these ‘rebellious atoms’ is calculable and is very well described by what is known as a Boltzmann distribution. The practical implication of this is that one should keep the irradiation intensity low if one does not want too many electron transitions outside the desired range. In plain English: less light, fewer rebels. Or: with RA-4, less light means better prints. And for that reason alone, a sodium street lamp is useless. Due to its high radiation intensity, it would significantly increase the number of ‘rebel atoms’ in the emulsion layer (as a photographer, it’s better to call this ‘fog’) and thus result in unusable images. Furthermore, street lamps are by no means pure sodium vapour lamps and do not emit light solely within the sodium spectrum; macroscopically, they therefore do not ‘match’ the requirements of RA-4 paper in any way. That is why Duka uses clean sodium vapour lamps with a narrow-band spectrum. These are also further spectrally limited by filters (in the order of 589 nm ± 5). And they are dim, precisely because of the Boltzmann distribution (we don’t want any ‘revoluzzer atoms’) of the possible excitation transitions in the paper. Oh dear. I’ve just ploughed through quantum chemistry with a sledgehammer. I hope that’s forgivable. Best regards, Franz

Renate

Hello, First of all, a clarification: there is no such thing as quantum chemistry. There is only quantum physics. Chemistry is a specific application of physics. I have never seen a sodium vapour lamp in an electrical shop. Nor can I think of many uses for sodium vapour lamps. Even street lighting is mainly powered by mercury vapour lamps. It is more of a niche product, which makes it expensive to manufacture. Sodium vapour lamps require a ballast and are not dimmable. That is why the Duka 50 has an iris diaphragm that allows you to adjust the brightness. However, the most expensive part of this lamp is the bulb (light source in standard German), and it has only a limited lifespan. I use light-emitting diodes (LEDs) for colour developing agents. However, the designation ‘yellow’ is not sufficient here. You should ensure that they are specified with a wavelength of 590 nm. This is close to sodium light. Unfortunately, the spectrum emitted by the LEDs is not as narrow-band as that of a sodium vapour lamp. Yellow LEDs also emit a little light in the green spectrum, which creates a coloured fog. That’s why I’ve fitted an orange filter in front of the LEDs. A suitable coloured plastic sheet, the sort often found in stationery shops (depending on the fashion trend), will do the trick. What’s more, LEDs are excellent for dimming. My light is set so dimly that I can just about make out where things are. There’s no need to be able to see the development process, as you can’t develop RA4 by eye anyway. You can only assess the image or test strip once it’s dry and held up to a lamp that you’ve designated as your standard. Incidentally, the same applies to black-and-white development. All red LEDs also emit a little light in the orange and yellow spectrum. That’s why I’ve fitted a dark red filter in front of the LEDs. Only then does the lamp pass the haze test. Best regards Renate

cfb_de

Hello Renate,

First of all, a clarification: there is no such thing as quantum chemistry. There is only quantum physics. Chemistry is a specific application of physics.

It may well be that, as a physicist, you see it that way. However, as a chemist, I am quite familiar with the term ‘quantum chemistry’ as a branch of physical chemistry. And I don’t seem to be entirely alone in this view, as there is even a rather significant specialist journal on the subject: the ‘International Journal of Quantum Chemistry’. http://www3.interscience.wiley.com/cgi-bin...ETRY=1&SRETRY=0

I’ve never seen a sodium vapour lamp in an electrical shop before.

That doesn’t mean they don’t exist. Here, for example, you can buy quite a wide selection: http://www.eshopmall.de/Haushalt-14/MCS_La...ages_30_15.html. As they can be found at almost every pedestrian crossing, I wouldn’t necessarily assume they’re a niche product. One could also – in your own words – say that your statement is simply wrong!!! Best regards, Franz

Renate

Hello, Unfortunately, the shop Franz mentioned is a bit of a let-down. The lamps advertised there are not sodium vapour lamps, but high-pressure discharge lamps containing a mixture of gases. Whilst part of the gas is sodium, the other part may be xenon, mercury, amalgam or something else. A colour temperature of around 2000 K is specified for all the lamps, and that is not suitable for monochromatic light. The light contains varying proportions of the entire spectrum, which makes it unsuitable for a darkroom. It should also be noted that these lamps must never simply be screwed into a suitable socket. Without the appropriate ballast and ignitor, they will either not work at all or a short circuit will occur after a while. Osram and Philips also manufacture pure low-pressure sodium vapour lamps. These have an SOX base. They would actually be suitable for the darkroom. I think I could even find a supplier. But why bother? It’s easier and much cheaper with LEDs. Incidentally, in the area where I live, pure sodium vapour lamps are rarely used in road lighting. So I stand by my statement that it is a niche product. Best regards Renate

kohlenklau

Hello everyone! I’ve just stumbled across this thread. I use a yellow 12V LED spotlight as my Duka light, with the light filtered through a brown jam jar. It works a treat as indirect lighting. It costs next to nothing and is great fun! This is just a suggestion, but for SW multigrade, a red LED spotlight with an E27 socket, screwed into a standard lamp, works brilliantly. Regards, Michael