Are Red LED'S ok for red safe light ?

I bought one of these on a lark to try it out.

http://www.goldengadgets.com/product_info.php?cPath=12&products_id=360

It really works great and it is bright. It will fog paper when put in direct light at several feet, but bounced off of the ceiling it causes no problems, and makes the darkroom liveable. It is bright enough that I can judge prints by without turning on the light. Cheap too.

Patrick

PeterB said:

Hi Lee,
unfortunately we can deduce nothing at all from that graph. You state the reason why yourself "No attempt was made to correlate the vertical intensity/sensitivity scales" in fact to make matters worse, one scale is linear the other log and they are different units!

The best thing to do as you say is to test !!

regards
Peter

Click to expand...

I agree. I have previously posted on this confusion. The arithmetic scale of the LED graph completely hides from casual view the fact that photographic materials are sensitive at low light levels (thank heavens!) and if you draw that graph with a log vertical scale you will see heaps of overlap with the paper sensitivity.

Try looking at the LED by reflecting the light from the base of a CD at the angle that gives the "rainbow effect" to give some idea of the spread of colours. I tried it with some amber LEDs about which I had high hopes, and found not only yellow but aqua! Needless to say, they fogged until I placed a sheet of Rubylith over them.

Incidentally, those LEDs I had chosen because they had a narrower spread than most, according to their specs.

As has been said, it all depends on the LED. The graph in the earlier post shows a pretty typical LED spectrum. SuperLEDs have a somewhat narrower linewidth. The problem is that some hight intensity LEDs operate at a shorter wavelength (more yellow), partly because the eye is more sensitive there. If you stick with the 645 to 660 nm red LEDs you shouldn't have any problem. I have used a pretty bright LED safelight with orthochromatic materials (like Kodalith) and paper with no problems at all. As for comparative brightness, they are quite bright, but the usual multi-LED module is nowhere near as bright as the Thomas safelight (which I find far too bright). The deep yellow and orange (590 - 620 nm) LEDs should also work well with the usual papers. (Forma claims to need deep orange or red safelights.) If you hunt hard you may even find LEDs that emit at 602 nm, which matches the Series 13 safelight filter for Kodak color papers. As with any safelight, a test should be done with the materials you intend to use. One decided advantage of LEDs is that they start instantly, so you can connect them to the enlarging timer. They are also miserly on power. Although LEDs have an inherently long life, they are sensitive to line spikes and surges, which can burn them out quickly.

Several of us have tested and found that even amber LEDs can work fine at surprisingly bright light levels. I can even use mine for colour if I turn it right down to a level that I can just see the image come up in the tray with dark-adjusted eyes. Safe time at the trays is only 2 minutes though so I keep the paper shaded most of the time and turn the wick down further.

Mine is just a metal box with an adjustable current source for the LED. Power is from the usual type of plug-in dc power supply. The only slightly unusual thing is that I have LEDs soldered to 2.5mm dc power plugs and the box has a corresponding socket so I can plug in different LEDs. In retrospect, the variable current is over-kill as I only ever use it full blast when doing b&w - colour could be taken care of by simply shading most of it it with black paper. A simple power resistor would do almost as well...

I uploaded a pic in another thread: (there was a url link here which no longer exists)
and attached a close-up below.

Cheers, Bob.

I purchased this bulb from superbright LEDs:

Dead Link Removed

I use it in a small aluminum utility housing pointed at the ceiling in a small bathroom I use as a darkroom. I have tested it with VC papers and with xray film and found that it does not fog either in 5 minutes.

I used a red LED from Radio Shack to make a darkroom flashlight

the LED's emission was right in the middle of the part of the spectrum you'd want for a safelight...I forget the wavelength...but it was printed on the package & I called Kodak's 1-800-242-2424 tech support to check

ANYWAY...I wanted to pass on how I made the flashlight since it was so simple:

get a red "jumbo" LED from Radio Shack ( the BIG one ), a plastic film container, some aluminum foil, and 2 AA batteries

fold over a couple layers of the foil and put that in the bottom of the plastic film container

poke 2 holes in the top of the film container & slip the leads for the LED through the holes and bend them over so the LED won't fall out

put 2 AA batteries in the film container...one + side up, the other + side down

when you put the top back onto the film container ( if you line everything up carefully ) VOILA the LED is on and works great as a red darkroom flashlight....to turn it off you only need to pull one side of the top up -- you don't need to completely remove it.

I made one out of desperation when I was temporarily without a normal safelight....I never need to use it anymore, but I always loved it since it was so simple and worked pretty well

I just got my order of these from Superbright...

PRODUCT INFORMATION--

Quantity: 5
Product: E27-x8-G LED bulb $ 3.95 (each)
Options: Red

They work great. No fogging from 3 feet (1 meter) during paper processing. Nice and bright. about twice as bright as the christmas tree red lights I was using.
Dennis

I am using two of the Optiled Red lamps in my darkroom with VC papers and have had no problem.
Neal

DarkroomExperimente said:

I used a red LED from Radio Shack to make a darkroom flashlight

Click to expand...

FWIW, SuperBrightLEDs sells LED flashlights of various descriptions, as well as LED flashlight bulbs for use in "generic" flashlights. I've got a little red LED keychain flashlight. It's handy for shining light on the enlarger lens's f-stop scale or finding bits of dropped paper. I also take it out with me when I take photos at night, since it's so small.

It's easy, the cheapest red LED deco light f.e. for clamp lamps will do the job with every kind of bw paper. Anything else than red must be tested seperately with every kind of paper you use, no matter how cheap or expensive you lamp was. Red is always safe, but orange that I mostly use is more conveniant. Yellow is mostly unsafe. There is absolutely no need to buy expensive safe lights for bw nowadays. The old safe lights with light bulbs and filters are a deal worse.

Best - Reinhold

grommi said:

Red is always safe...

Click to expand...

Not always.

Most, if not all, red LEDs also emit small slivers of blue and/or green light. You can't see them with the naked eye as they are overwhelmed by the safe red light. But if you go into a completely dark room and carefully observe the red light as reflected from the business side of a common CD, you might be surprised. The CD acts as an inexpensive prism, breaking the light up into its separate wavelengths.

Because the slivers are small, if your normal working procedures only expose the paper to the safe light for a short period of time, you might be all right. But if, like me, you often find yourself in a complex and lengthy dodging and burning session, you might begin to experience subtle fogging. I did using 635nm red LEDs.

The solution is to filter the red LEDs with a single layer of Rubylith.

Ken

I made fogging tests with several common red LED sources and up to 10 minutes I got absolutely no fogging at all, I made it properly with pre-exposed paper. Even a cheap bicycle tail light was perfect, assuming you don't aim with the light directly on the paper from a few centimeters distance. Besides that the corner with the enlarger should always be blocked from direct light beams, no matter which source you use.

Jobo used to make an LED safelight that looked Amber and they claimed itwould even be safe with Colour Ppaer, (but that was in the days of EP-2 Colour Ppaer) they called it JOBO Minilux if anyone whats to go searching.

I used red LED brake lights driven by a 12V supply, and red LED Christmas lights with no ill effects. These were great for lighting areas of the darkroom where the main safelight didn't quite reach. The standard test is to put out a piece of enlarging paper with something on it for five minutes. If there is no shadow then the light is safe.

I purchased Red LED Lamps from Superbright. I initially tested for fogging (using Kodak instructions) and found that I could get limited time (3 minutes) with Ilford VC Resin coated paper with 2 lamps bounced off of a white ceiling. This is in an 11 x 14 darkroom.

When I tested Arista EDU VC R/C paper I found it much more sensitive.

I finally placed one lamp in a globe fixture in the center of the ceiling and put a layer of Rubylith over the lamp (not the globe). That got me to 7 minutes, but it is still plenty bright. I can read instruction sheets, a stopwatch, etc by the safelight alone.

I went through a lot of paper, but in the end it was well worth it.

Mike-D said:

I used red LED brake lights driven by a 12V supply, and red LED Christmas lights with no ill effects. These were great for lighting areas of the darkroom where the main safelight didn't quite reach. The standard test is to put out a piece of enlarging paper with something on it for five minutes. If there is no shadow then the light is safe.

Click to expand...

This test is a bit too simple.

You need to use paper that has been pre-exposed to a slight fogging exposure. And it is best to add a test with paper that is post-exposed to a slight fogging exposure.

And five minutes might be a little short, if one is used to using some fairly complex printing regimes.

dbuchheit said:

I initially tested for fogging (using Kodak instructions) and found that I could get limited time (3 minutes) with Ilford VC Resin coated paper with 2 lamps bounced off of a white ceiling. This is in an 11 x 14 darkroom.

Click to expand...

This observation comes up often. The answer is always the same. Filter your red LEDs with a single layer of Rubylith. You will notice no difference in the brightness of the red light. But your safe time will skyrocket.

My safe time, tested using red LEDs, Rubylith, and the method described by Matt (which is the only meaningful test method for paper fogging), exceeds 60 minutes when using Ilford MGIV RC. I stopped the test as being pointless beyond that.

If you are only getting 3-7 minutes safe, then your red LEDs are also emitting tiny bits of blue and/or green light. Most do. You can't see it with the naked eye. Check by reflecting your LEDs off the surface of a common CD. It acts like a prism.

[Edit: I see you did mention using Rubylith. Did it completely cover the globe? I'm using a strip of six 1-watt red 635nm LEDs. They sit atop a Thomas Duplex suspended from the ceiling. It's a smallish darkroom, only about 8x11-feet. My LEDs are light-tight under the Rubylith.]

Ken

Go to photo.net and look for safelights on the cheap.

Chris

Yes, my lamp is wrapped light tight, and is inside a globe.

hi all

I had a load of white LED light tape like this

http://www.google.co.uk/search?q=le...yIGoCQ&sqi=2&ved=0CAcQ_AUoAA&biw=1680&bih=952

left over from a job and just covered it with Rubylith

works great and did not fog with a 30min test after which I got a bit board
it also makes my darkroom look a bit hi tech
I have put it under shelfs and other places that my over head never lit into

robin

london

dbuchheit said:

Yes, my lamp is wrapped light tight, and is inside a globe.

Click to expand...

If your working approach requires longer than the 3-7 minutes (mine often does), and a CD test shows no "bad" light being emitted from the LEDs, then you might also try looking for conventional light leaks. The Rubylith should do the job if the LEDs are the only source of light in the room. (See above post.)

As for me, old habits die hard. No matter that I know my red light is safe, I still keep an oversized sheet of beat-up black construction paper handy and will instinctively cover the exposed sheet of paper in the easel each time I step away for a moment. I just can't break that habit.



Ken

Ken Nadvornick said:

If your working approach requires longer than the 3-7 minutes (mine often does), and a CD test shows no "bad" light being emitted from the LEDs, then you might also try looking for conventional light leaks. The Rubylith should do the job if the LEDs are the only source of light in the room. (See above post.)

As for me, old habits die hard. No matter that I know my red light is safe, I still keep an oversized sheet of beat-up black construction paper handy and will instinctively cover the exposed sheet of paper in the easel each time I step away for a moment. I just can't break that habit.



Ken

Click to expand...

Actually, 7 minutes is plenty long for me. I used to do mostly color and as such was in total darkness. I usually us the safelight now if I can't work by feel, misplace something or get disoriented.

Ken Nadvornick said:

If you are only getting 3-7 minutes safe, then your red LEDs are also emitting tiny bits of blue and/or green light. Most do. You can't see it with the naked eye. Check by reflecting your LEDs off the surface of a common CD. It acts like a prism.

Click to expand...

I knew we are not done with that subject.

A CD does not(!) work like a prism, the colours are made by interference. It's physically impossible that a red LED emits shorter wavelengths. A LED can emit longer wavelengths = less energy, this is f.e. done with blue LEDs by targeted contamination of the light emitting substrate so that they can act as a white LED. You can't get green light = more energy from a red LED. LEDs with the basic blue green yellow orange or red colours are practically monochromatic with an emission spectrum that is typically only 25 nm wide.

I verified this with my selfmade orange and red LED safe lights. With reflection from a CD you can see all colours our eye can see from deep blue to dark red. With a real prism there is only orange or red and absolutely nothing else.

If an additional filter makes your red safe light "safer", there's something wrong and you don't have a red LED but maybe a white one with a colour layer to imitate a red LED.

sources:
http://en.wikipedia.org/wiki/Light-emitting_diode
http://en.wikipedia.org/wiki/File:Red-YellowGreen-Blue_LED_spectra.png
http://commons.wikimedia.org/wiki/File:LED_Spektren.jpg
and my darkroom

grommi said:

I knew we are not done with that subject.

Click to expand...

OK, it's always best to keep an open mind, so...

How then does one explain and reconcile the following two direct observations?

(1) In a darkened room light from a 635m red LED is reflected directly off the recording side of a conventional CD disc. In addition to the dominent reflected red color one can also make out small but disinct blue and green slivers of reflected light. No other reflected colors are visible. Then, without changing anything else, a single sheet of red Rubylith is placed between the LED and the CD and the observation repeated. The dominent red is still there. But the blue and green are now missing. There is no longer any visible trace of them. If the Rubylith is then removed, the blue and green are again visible. Changing the angle of observation had no effect on the blue and green colors.

(2) In a darkened room a sheet of b&w photographic paper is pre-fogged to just below threshold. Then the standard safelight test is performed under the light from six 635nm red LEDs. After processing there is distinct evidence of fogging after several minutes of exposure. Then, without changing anything else, the LEDs are placed under a light-proof covering of red Rubylith and the test is repeated. After 60 minutes of exposure the paper is processed. There is no visible evidence of fogging out to the maximum exposure. The paper is then checked with a reflection densitometer, which confirms there is no fogging.

In the first case, if the blue and green colors were somehow being generated on the CD side of the Rubylith, then the addition of the filter should have no effect. Except perhaps to slightly lower the intensity of the LED's red light if the color of the Rubylith was not a perfectly transparent match. If, however, the blue and green were being created on the LED side of the Rubylith, then the filter should indeed remove them.

In the second case, the exact same logic applies as in the first case. Except that the human observation has been replaced with a sheet of b&w photographic paper that is sensitive to blue and green light, and is examined after the test by an instrument. In effect this substitutes an objective non-human observation for a subjective human one.

And in both cases the final observational results match each other.

(My darkroom where I performed these observations is perfectly dark by design and lots of effort. There is no extraneous light. I have purposely sat inside in the dark for 60 minutes, then scoured the door frame and all other corners for light leaks. There are none. Even with a floodlight on the outside pointing at the door. When I have open boxes of 8x10 film on the counter, I don't want to have to worry.)

(The paper used in the fog test was Ilford MGIV, selected precisely because it is sensitive to both blues and greens.)

(I understand the principle of constructive and destructive thin film interference.)

Ken

LEDs can emit higher and lower wavelengths around its centre peak. Many others have documented this (e.g. here (there was a url link here which no longer exists))

At least two explanations include:
1. Overpowering them which widens their spectral bandwith
2. Dopant contamination ((there was a url link here which no longer exists))