Sigh. Just when you think you've got your safelight issues all figured out...

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clayne

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ADOX Vario Classic FB, 4s pre-flash, 5m safelight, 3m development. One set near the enlarger, another set near the trays. Paper normally takes 2-3m of development.

Guess it's not so safe. Knew there was a reason I was fighting with prints more than I should have been. Have a sheet sitting in the dark for around 10 minutes now to see if it's a stray light source.
 

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clayne

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Update: Wasn't a stray light source, just a lame safelight bulb.
 

Rick A

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Okay -- now tell all the rest of us what your safelight setup consists of. What color, bulb type and wattage,etc. Are you using an OC filter or RED? Is the bulb a 15w tungsten or a new CFL type? If its a CFL, toss it, there are plenty of posts here that give reasons.
In all my years, i've only used red with no greater than a 15w tungsten bulb, and presently, my lamp is one meter from my work area. I've gone as long as 10 minutes without any fogging showing up. I figure that having my paper laying open longer than that, is asking for trouble AFAIC.
Did you look at the safelight requirements for your paper? Most European paper manufacturers specify RED safelights.

Rick
 
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clayne

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Red 25w, unfrosted, incandescent. About 2.5 meters above my head shooting straight upwards and bouncing off ceiling which is atleast 4m high. 5w, opaque, same position fogs nothing - of course I can barely see as well.
 

ic-racer

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A red bulb?? Did you really think that was going to be safe :smile:
 

hrst

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Make your own from red leds. They don't in practice produce wavelenghts shorter than yellow at all, so you are safe even without any filters. Filters can always fade etc.

If you want to be on super-safe side, use red leds with safelight filter :D.

This way you can use HUGE safelight levels, probably more than you even want.

I tested 625 nm 1-watt red leds (these: http://cgi.ebay.com/10-PC-1W-StrawH...emQQptZLH_DefaultDomain_0?hash=item3a4d73a9f1 ) adjusted to a level that gives an enormous light level never normally needed in darkroom, and still I needed at least 5-10 minutes to show any fog at all. One of these leds is enough for even a larger darkroom, or you can use multiple in many places dimmed down to safe levels. If you don't like wires, you can use them battery-operated since they draw so low current. You won't probably use the whole 1-watt power. I used 600 mW in my test and it was more than ever needed.
 
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It's not that I thought the safelight was 100% safe - it's that the distance seemed relatively safe. By the time the light banks off the ceiling and hits the paper it's traveled atleast 15-20 ft. It was unsafe enough that it was probably muting my whites causing me to chase brightness around in my prints. Anyways, the 5w will have to do for now but I'm definitely on the hunt for some LED safelights. Thanks for the pointers to that specific LED, hrst.
 

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The postage for a mail-ordered safelight (not a bulb) might be more than the cost of the safelight - but you can combine it with a film order, paper etc etc. It could be simpler than fiddling around with a homemade version. A 'real' safelight can also frequently be found in second-hand shops, here at least, though you'd be wise to buy a new filter-glass I guess !
 

hrst

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Yeah, in fact every red led will work. The one I referred to is just an example of a cheap, powerful Chinese led Ebay is full of.

Orange or even yellow leds will work too, but it's nearer to green and may cause problems with some materials and with high illumination levels.

DIY LED safelight can be in fact much safer than some old found from second-hand shop. They use normal bulbs that produce HUGE amounts of green&blue light that will instantly fog the paper if the filter is not perfect or near to perfect. And, filters fade as they get older. Professional standards ask to change the filters every year or something like this.

Most safe is to find this kind of cheap safelight, maybe with faded filter, and replace the bulb with leds.

Leds usually go about 50-100 nm around the peak wavelength. So, a 625 nm red led can produce very small amounts to 575 nm (which is greenish yellow; okay for most papers in small amounts). If you want to be sure, just look at the datasheet of the led. But usually it's cheaper to just buy these unspecified Chinese red leds and test them.

If you need assistance in electronics and how to build a safelight from bare leds, ask me. You will need one resistor and a standard DC wall adapter, and a digital multimeter is nice to have.
 

craigclu

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If you need assistance in electronics and how to build a safelight from bare leds, ask me. You will need one resistor and a standard DC wall adapter, and a digital multimeter is nice to have.

Could you post the info somewhere or as a response in here? I've been toying with this thought and would be interested in what is required. Thanks!
 

Nicholas Lindan

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A clear red lamp will work - if it is the right type. Many years ago GE used to sell red lamps designed for safe-light duty: very safe, quite bright.

CPM Delta and Kalt sell dipped bulbs. Osram (?) clear safelight bulbs were available a few years ago.

You can dip your own 7 1/2 and 15W bulbs in Rosco Colorine 7610 (Red #27 (Wratten sort-of-equivalent)). Search Google groups rec.photo.darkroom for Lloyd Erlick's post on the subject. It was only 3 years ago that rpd was still active ...
 

hrst

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Okay, so, basically all the leds will need is a circuit that restricts the current I. This circuit can be just one resistor, if the voltage stays at quite constant level.

If you just connect one led:

Take any basic wall adapter found everywhere that gives DC output (direct current). Voltage has to be at least about 3-4 V, and preferably not too high (much over 12 V and you are wasting much power as heat). You can measure the voltage, since many wall adapters give even 1,5 times more voltage than specified when little current is drawn.

Red leds have a voltage drop of about 1.5 ... 2.0 V. The idea is that the rest of the voltage is used in the resistor.

Connect the resistor's first end to the one of the wires coming from the wall adapter. Then connect the LED between the another wire and the another end of the resistor. So, the resistor is connected in series with the LED.

In LEDs, the longer leg is + and the shorter is -. However, some cheap Chinese leds may have them swapped and that's why they are cheap. If the light doesn't work, try to turn the LED around.

The correct resistor value can be calculated from: R = ( Usource - Uled ) / Iled. Iled is the current of the led. Traditional "high-brightness" leds can usually take 0.03 A to 0.05 A max. 1W high-power leds can take 0.5A but that's probably much too much and produces much heat in both led and the resistor. Using these 1W high-power leds, even 0.1A gives you a great illumination, using just one LED.

Then, the heat that is produced in the resistor, can be calculated as P = (Usource - Uled) * Iled. Multiply this by two or three and get a resistor with that high power rating.

An example:
6V wall power supply, 1W red power LED.
Let's decide that 0.1 A is enough current for LED. We can change this later it there's not enough light.
The correct resistor value is: (6V - 2V) / (0.1 A) = 4V / 0.1A = 40 ohm.
Resistor generates heat: 4V * 0.1 A = 0.4 W. So, take at least 1W resistor and allow it to cool down in free air.

Many Chinese Ebay sellers send you "free" resistors for 12 volt power supply with the leds to make things easier.

You can use a soldering iron but if you don't have one, you can live without, using screw connections or something like that.

If you want more leds, the easiest way is to connect them to series. Just the minus of the previous led to the plus of the second one. Then the LED dropout voltage is the sum of all the LEDs. So, the minimum voltage of the wall adapter is higher then.

That's it. Quite a complete description. If this is not clear enough, please don't hesitate to ask.
 
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polyglot

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A couple of points in addendum to hrst's post:
- it's easier if you buy a switchmode or regulated wall-wart because these have constant output voltage regardless of load, unlike the transformer type.
- if you have a multimeter, measure the voltage drop across the LED while it is dimly lit, i.e. with about half or quarter as much current that it's rated for
- if you have a higher supply voltage like 12V, it makes sense to put multiple LEDs in series with one resistor as it's much more efficient and uses less resistors

So you would do some experimenting in this order:
- Look up the LED datasheet, which will specify a maximum current. Likely to be about 10mA for a tiny indicator LED and maybe 700mA to 1A for a big lighting LED
- Datasheet again, look for the "forward voltage", Vfwd. Should be about 1.5V, might be slightly higher.
- Decide what size resistor you need to put about 1/4 of the max current through it from your supply:

Itest = 0.25 * Imax
Rtest = (Vsupply - Vfwd) / Itest

For example with a 100mA-rated LED, Itest = 25mA. If Vsupply is 12V and Vfwd is about 1.5V, then Rtest = 420 ohms. Pick the next highest value in the series, which is 470 ohms. Wire up your supply, LED and resistor all in series and the LED should glow, though not necessarily very brightly. Put your multimeter in Voltage mode across the LED and measure the voltage drop. Now you know the exact Vfwd for your LED. Do this for a few LEDs.

Say you have 4 LEDs that you measured at 1.51V, 1.58V, 1.49V and 1.55V respectively (they will vary but probably not this much). When you put them in series, the voltage drop will be the sum of that, i.e. 6.13V - that's the forward voltage of your whole string of LEDs.

Now you need to choose a resistor to set the current in the string, using the same formula as above and a chosen current that is about half of the rated current:

R = (Vsupply - Vfwd) / I

Since for this example the LEDs are rated at 100mA (making them 150mW LEDs; 0.1A * 1.5V = 0.15W), we want to run them at about 50mA. That gives us R=117ohms and pick the next lower value in the series, which is 110 ohms. 100 ohms would also be OK - just means you're running them at slightly more than half their rated current. The number of LEDs you put in series is limited by your supply voltage, you need to have a little voltage left over for the resistor to drop, preferably no less than about 3V on a 12V supply. If you have a too-small voltage for the resistor (too many LEDs) then your current regulation will be poor: you may get a very different current and blow an LED.

The total current drain on the supply is the number of LEDs you have in parallel, not series. So if you have a chain of 4 LEDs in series running at 50mA, the total load is 50mA. However if you connect 5 LEDs in parallel (each must have its own limiting resistor, you can't use one limiting resistor for several parallel LEDs), the total load will be 250mA. If you like, you can make up multiple LED/LED/LED/LED/R chains and place those in parallel. That way you could have for example 20 LEDs for a total load of 250mA on the supply.
 

Anon Ymous

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...Take any basic wall adapter found everywhere that gives DC output (direct current). Voltage has to be at least about 3-4 V, and preferably not too high (much over 12 V and you are wasting much power as heat)...

So, a mobile phone charger is probably fine for that purpose eh? Additionally, you can also have a switch to use red or whatever other LED color you wish, depending on the paper you use.
 

hrst

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Yes, phone charger is probably a very good choice.

Traditional electronics is a nice hobby in addition with traditional photography, you can make all kind of small gadgets for darkroom and cameras. I've made eg. preflasher with adjustable color balance for color work and a timer 1 - 12 sec.

Making a safelight works as a very simple, "entry-level" exercise to electronics :smile:.
 

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Check out www.superbrightleds.com/specs/E27-W24.htm I've had good luck so far with their red bulbs. They have all the circuitry built in. Just screw them into a fixture. You don't need to build any circuitry at all.
 
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Matching color of the safelight to your paper becomes important if you ever get into lith printing. Then it becomes a real problem, because often you find yourself rocking trays for as long as 20 or 30 minutes for one print. I like a purpose built darkroom safelight. I use the red jumbo bulbs. They are about $20 a piece, but they last a good long time and illuminate my darkroom nicely.
You screw it into a socket, and turn the power on. Done.

Dead Link Removed

- Thomas
 
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I use the red jumbo bulbs. They are about $20 a piece, but they last a good long time and illuminate my darkroom nicely.
You screw it into a socket, and turn the power on. Done.


Boy, am I glad to read this, i was starting to think an electronics course was needed just to get my safelight on:
 
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clayne

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Not that I necessarily disagree with Thomas, because he knows his stuff, but I did use a similar bulb (difference was mine was not frosted or opaque) and ran into these initial issues. The opaque ones just might be fine at 25w if distance is reasonable (atleast 8 ft away and bounced). But do what sane people should do: test.
 

hrst

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Normal tungsten bulb with red paint cannot be used. It has to be designed for darkroom use so it completely blocks UV, blue and green wavelengths. Some brands may be designed that way but you never know unless you buy darkroom bulb. Some brands may work just by luck. You can't see the difference by eye.

However, bulbs using red LEDs will work at reasonable illumination levels, even if not designed for darkroom use.
 
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It's not only an issue of 'coloring' the light emitted from the bulb red.

It is also an issue to filter all other light out, except infrared. This takes some serious spectral analysis or trial and error by experimentation. By the time you're done, it's probably cheaper to purchase the purpose built bulbs anyway.

I like the idea of LEDs, most of all their longevity. But I would not use one unless it was of a kind sold commercially, purpose built for darkroom use. It's as much a crap shoot as anything else where you do the R&D, be it incandescent bulbs, fluorescent tubes, or LEDs.

I also think of the torment of testing all those bulbs, just to be safe. Peace of mind is cheap at $20. :smile: You know, one less thing to worry about.

Not that I necessarily disagree with Thomas, because he knows his stuff, but I did use a similar bulb (difference was mine was not frosted or opaque) and ran into these initial issues. The opaque ones just might be fine at 25w if distance is reasonable (atleast 8 ft away and bounced). But do what sane people should do: test.
 

hrst

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Thomas, please note that a traditional commercial safelight is not fully safe and easy way. The traditional saying goes: "there is no safe safelight", and it's quite true, especially when using old technology. Even if you buy a commercial unit, you may and eventually will need to test it. The distance matters, the brand matters (some may be worse than others in filter quality), and the filters fade as time goes by, if they are incandescent/fluorescent based like many or most still are.

I may be repeating myself but I'm really love with LEDs and with a reason :D. They really don't practically produce wavelengths that would need to be filtered out. They are not perfect at all but every time I've tested leds with BW paper, I get much lower fog than with any commercial darkroom light I've tried. This may be because of filter fade present in the old units.
 

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Normal tungsten bulb with red paint cannot be used. It has to be designed for darkroom use so it completely blocks UV, blue and green wavelengths. Some brands may be designed that way but you never know unless you buy darkroom bulb. Some brands may work just by luck. You can't see the difference by eye.

However, bulbs using red LEDs will work at reasonable illumination levels, even if not designed for darkroom use.

You can see if a lamp is safe or not to some extent. A prism will show the spectrum of the emitted light, but if you don't have one use a CD. The reflection on the under side will do the same.
 
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