My LED Darkroom Safelight

Today I decided to get those parts I had laying around into a useful darkroom. I boarded up the bathroom window, make some workspace and then wend to Radio Shack to get some components for the LED safelight I wanted to make. I wanted to go LED because they put out a specific wavelength, in the case of red, my LEDs are about 640 nanometers (I forget the exact figure but it's -+10 nm). I used 2 1W high power LEDs powered by a 9V battery, calculators online can tell you how big a resistor is needed given the arrangment of LEDs and the power requirements of source and forward voltage etc. I popped all the junk into a project box with a switch and there we go. Its really bright and shows no signs of fogging the paper I was cutting and getting ready so far. It's bright enough that it lights up the whole bathroom when placed on the closet door, bouncing off the ceiling.

Nice job!

When you get a chance, you may want to go find an old CD/DVD and observe the red light as it's reflected off the recording side of the disc. The disc will act as a simple prism and break the light up into discreet color bands.

Look closely and make certain your LEDs are not also emitting small slivers of blue and/or green light. Too faint to see with the naked eye, but enough to sometimes cause slight fogging in your print highlights. It's not unusual for red LEDs to do this, regardless of what the specs say.

My 635nm red LEDs showed both blue and green spikes. If yours do as well you may need to add a single layer of Rubylith as a filter. This will fix the problem. Also make sure you perform a pre-fogged safelight test with whatever paper you are using.

Ken

Ken,

Thanks for the tip, I checked with a DVD and unless I'm doing it wrong it's only emitting red. Which is great, because I went through this whole process to avoid having to use filters and that sort of thing.

A friend advised me to do the kodak safelight test. Well worth doing and more accurate than a simple coin test.


BTW, I made a similar one to yours, I used regular red LEDs and I made an array with 24 of them running of an old wallwart. I put them in a red aerosol can lid and it passes the safelight test.

twalsh341 said:

I checked with a DVD and unless I'm doing it wrong...

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Probably not. If the spikes are present they're pretty obvious. Small, but obvious. I noticed mine right away. So have most others who have seen and reported them.

Sounds like you are good to go.



Ken

fran said:

A friend advised me to do the kodak safelight test. Well worth doing and more accurate than a simple coin test.

Click to expand...

I'm with Fran on this one. Please do the Kodak test, it will only take 10 minutes and it will save out $$$ in paper, but above all, in frustration spent in chasing good contrast. The test is here: http://www.kodak.com/global/en/consumer/products/techInfo/k4/k4TestSafelite.shtml

Coin test does not tell you the full picture. You may have a safelight that passes it, but which can still fully depress the highlights in your prints, causing you to overcompensate with high contrast settings.

Second to this, in importance, is making sure your enlarger does not leak too much light.

Well done for building such a neat device.

Ps. My LED safelight works but it required an addition of a red filter. LEDs differ, and even the purest deep red, as checked by the CD/prism test mentioned by Ken, will affect paper if too bright.

I have made a few LED safelights and I have never found an orange or red LED that emits anything like a single wavelength. If yours pass the CD test showing red only, can you tell us the part number please?

Michael,
That is stinkn' simple, and to think I sweated so long waiting for the right deal on a Thomas safelight

Thanks for sharing the project.

Steve