Dimmable LED safelight solutions

[Gallery 44]

HI APUG

I am helping out at a not-for-profit artist centre in Toronto and the centre is looking to upgrade it's existing darkroom lighting system for two darkrooms. The current system is a mashup of kodak and ilford made safelights, fluorescent light boxes with rubylith filters, and darkroom 'safe' LED lights (safe for a limited time, varies from paper to paper).

The ideal upgraded system would be:
1. Dimmable (users of the darkrooms have noticed the existing 'safe' LED lights to cause fogging, so dimming the LEDs would allow for longer periods for paper to be out)
2. Selective so as to only illuminate the walking paths of the darkrooms and only portions of the darkroom being used.

The system would be composed of multiple built-LED arrays positioned in different locations in the darkroom so that the lights can be turned on/ off and dimmed depending the needs of the user.

So far, I have not come across any sort of pre-built darkroom 'safe' LED array, has anyone found anything like this? I am supposing the solution will have to be custom built, one idea is to repurpose LED stage lighting with red LEDs or with filters (http://static.bhphoto.com/images/images200x200/996876.jpg).

How would you guys go about this? Below are images of the two darkrooms.

Thanks for taking the time!

 

[John Koehrer]

For walkways, why not red or amber mounted near the bottom of the tables or kickplates Reflected from the floor They won't give enough light to fog the paper. Spaced ~12-18" apart or even just on corners.

Is the afterglow from the fluorescents part of the problem?

 

[Ken Nadvornick]

The ideal upgraded system would be:
1. Dimmable (users of the darkrooms have noticed the existing 'safe' LED lights to cause fogging, so dimming the LEDs would allow for longer periods for paper to be out)
2. Selective so as to only illuminate the walking paths of the darkrooms and only portions of the darkroom being used.

Welcome to APUG...

The existing LED lights are fogging because they emit tiny slivers of unsafe blue and/or green light. These colors are not normally visible to the naked eye.

To see them, find a common (already recorded) CD or DVD disc. Darken the darkroom completely, except for the red LEDs. Place the disc right next to the LEDs. Observe the LED light as it is reflected from the recorded side of the disc.

Look carefully for any faint narrow bands of blue or green light buried within the otherwise overwhelming red color. If you see any (I have never seen a red LED where at least some were not present), that is the source of the fogging.

These emissions are due to the intentional introduction of chemical compounds (dopants) during LED manufacture. The unwanted light is easily removed by filtering through a single sheet of Rubylith. Once filtered, the red LEDs become very safe, and thus no dimming is required.

In my own darkroom I installed a bank of six 635-nm red LED bulbs. When unfiltered they fogged Ilford MGIV papers (both FB and RC) over a several minutes period. (Note that this was a proper pre-flashed fogging test.) Both blues and greens were visible on a DVD.

After filtering with a single layer of Rubylith I was unable to reproduce any discernible fog after 60 full minutes of exposure, at which point I terminated the test. No other color except red was visible on a DVD.

I have been successfully using these filtered red LEDs ever since.

Ken

 

[Gallery 44]

Is the afterglow from the fluorescents part of the problem?

John, Not that I am aware of at the moment.


Thank you John and Ken for the suggestions and info!

 

[pm5057]

If LED safe lights are still of interest, see here http://b-wtechnik.pp7.uk/led_safelights.htm