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  1. #21
    PeterB's Avatar
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    That graph has no value

    Quote Originally Posted by Lee L View Post
    This is an overlay of the sensitivity curve of Ilford MG-IV with the amber LED emission spectrum (the blue curve) I've been using with that paper. The horizontal wavelength scale is matched. No attempt was made to correlate the vertical intensity/sensitivity scales. You can see that the paper sensitivity is rapidly heading toward zero as it approaches the output of the LED. You should, of course, test.
    Lee
    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

  2. #22
    chrisf's Avatar
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    http://www.borealislighting.com/auroraradiance.html
    I'm using the M60 and haven't had any problems.

    chris

  3. #23

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    Quote Originally Posted by dpurdy View Post
    I jsut called the place that Sal recommended and asked about that led and the salesman told me it would be about the same brightness as a christmas tree bulb. so if that is the case I will stick with the xmas tree bulbs as they are very cheap and easy and don't fog the papers I use.
    I can't argue with your results but would advise that you not count on the christmas tree bulb's red paint maintaining its transmissive characteristics long term; do retest for fogging from time to time.

    As far as brightness, the red OptiLed puts out 45 lumens over a 130-degree angle. I don't know how many lumens a red 7 watt christmas tree bulb provides, but a similar white 7 watt night light version

    http://www.lightbulbemporium.com/pro...sp?prod=709007

    claims 35. The red paint must attenuate that quite a bit. I bounce one red OptiLed off the white ceiling of my roughly 6' x 8' bathroom when it's configured for printing. Things are comfortably bright, even for these aging eyes.

  4. #24
    Mike-D's Avatar
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    Going low tech, I used a short string of red LED Christmas lights to illuminate my cutting area which was a little dark. I removed a flasher circuit and added a resistor. Tested fine and works great.

    Mike D

  5. #25
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    Quote Originally Posted by dpurdy View Post
    this is probably a stupid question but just how bright are those led lights? Do they compare to a thomas safelight type brightness?
    The superbrightleds.com E27-A24 (595nm) mentioned earlier is supposed to be equivilant to a 15 to 20 watt incandescent bulb. That would be far dimmer than the Thomas unit with the vanes open.

    Murray
    _________________________________________
    Note to self: Turn your negatives into positives.

  6. #26

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    LEDs for safelights

    Quote Originally Posted by brucej View Post
    There are a number of red LED's on the market now I have been wondering if anybody has tried them as a general purpose safe light ?
    Not only are they safe, but having a very narrow "bandwidth" they are percieved to be much brighter. AND if you don't like red, you can use also use YELLOW LEDS. I have been using a set of 35 YELLOW Christmas LEDS for 2 years now and I find yellow is much easier on the eyes. My testing with several brands of B&W papers result in NO fogging even after 10 minutes of exposure. Typical price for a 35 light set is $13 but after the Holliday, can be had for $4 to $7.00. Try 'em, you'll like 'em.

  7. #27
    patrickjames's Avatar
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    I bought one of these on a lark to try it out.

    http://www.goldengadgets.com/product...roducts_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

  8. #28

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    Quote Originally Posted by PeterB View Post
    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
    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.

  9. #29

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    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.

  10. #30
    Bob F.'s Avatar
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    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: http://www.apug.org/forums/attachmen...8&d=1132187903
    and attached a close-up below.

    Cheers, Bob.
    Attached Thumbnails Attached Thumbnails sl2.jpg  

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