LED rope light for possible darkroom applicaton

DaveOttawa · Nov 26, 2010

It's not just about wavelength, an LED with a "safe" wavelength range (e.g. a red LED) can and will fog paper if there is enough intensity. I've attached the SED of a flashlight that I measured (that I use- carefully - in the darkroom), output is zero shorter than about 575nm but it will definitely fog MGIV RC paper if you hold it close for a few seconds.
The answer is always to test, there are detailed but easy to perform methods described on Kodak's site

john_s · Nov 30, 2010

thisismyname09 said:
......... LEDs will only give off a certain frequency of light, nothing more.............

Unfortunately this is not generally the case. I am using my mark 3 LED safelight after the first two (one amber, one orange-red) were found to fog VC papers (Agfa and Ilford). My current one has extreme red LEDs and is very safe even at a high intensity.

Try this (thanks to Paul Butzi for the idea):

Look at the light of the LED reflected from the base of a CD at the angle that gives the "rainbow" effect. You will probably be surprised to see quite a range of colours from red through orange, yellow, green and even aqua. I think it's hard to judge the amount of each colour, though.

The spectrum graphs supplied by LED manufacturers shows the spread measured in arithmetic units, not the familiar logarithmic units used by photographers, so the spread is worse than it seems from a quick glance of the graph.

If someone finds an orange LED with very little spread please tell us all!

michaelbsc · Nov 30, 2010

Mainecoonmaniac said:
michaelbsc said:

I don\'t have a bright darkroom. I use a few small 5x7 housings that I\'ve collected cheap over the years to illuminate specific work areas and let the rest of the room be dark if the white lights are off.

Searching the floor is a little hard if I drop something, since there\'s little illumination outside the spots. But I never worry about fogging anything.

Click to expand...

The Thomas Duplex safelight was a salvaged from my work place. It was 10 years ago when the university started closing darkrooms at reasearch labs. I also got an Arkay tumbling print washer too.

The safelight is good.

YMMV, but I think that print washer is an instrument of the devil.

pcyco · Dec 9, 2010

hallo

yesterday i tested the led again.
distance to the paper aout 30 cm.

12 minutes -> absolute nothing. white, white white.
--
thomas

Jerevan · Dec 14, 2010

I passed by the local store (local to my lab, anyway) the other day and asked them to get some of the red LED bulbs so I can try. Will report back when I get my hands on them.

totalamateur · Dec 14, 2010

I use a very bright red LED - probably 1 W and it will fog my ISO 3 homemade emulsions (which are not pan) if left withing 1 inch for 30 seconds. About the same for paper. I've never had any issue with fog at all, for any length of time (including the 2 or 3 hours it takes to make a liquid emulsion) at distances greater than a foot. For B&W papers and lower speed ortho films, there is very little risk of fog with Red LED's in my experience. You have to actually try to fog the paper/ortho film. I use the same light with Arista Ortho film quite often, and have suffered no ill effects.

PeterB · Jan 5, 2011

DaveOttawa said:
I've attached the SED of a flashlight that I measured

Dave, how did you measure that ? I've had a few LESs with different centre frequencies I've had for a while, wondering what I would use to measure their response.

Rgds Peter.

Mainecoonmaniac · Jan 8, 2013

I bought a set of red LEDs and strung them in my darkroom as safelights. It works well. I ran a test of exposing a sheet of paper for an hour with no fogging. You can also get orange LEDs too. I stopped using my Thomas Duplex safelight because the LEDs are so bright.

Take a look:
http://www.ebay.com/itm/Fad-Red-20M...4712482?pt=US_Light_Bulbs&hash=item3f20e362a2

Ken Nadvornick · Jan 8, 2013

Or even the quick-and-dirty CD test. You might be surprised.

Ken

LED rope light for possible darkroom applicaton

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