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.
This test is a bit too simple.
Originally Posted by Mike-D
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.
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.
Originally Posted by dbuchheit
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.]
Go to photo.net and look for safelights on the cheap.
Yes, my lamp is wrapped light tight, and is inside a globe.
I had a load of white LED light tape like this
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
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.)
Originally Posted by dbuchheit
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.
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.
Originally Posted by Ken Nadvornick
I knew we are not done with that subject.
Originally Posted by Ken Nadvornick
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.
and my darkroom
OK, it's always best to keep an open mind, so...
Originally Posted by grommi
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.)