LED safelight for Development by Inspection?

wdemere · Aug 26, 2004

I've been using a red led safelight for about 6 months now in my darkroom and it is extremely bright without fogging anything. I just plugged it into the normal room light and now don't even have a white light at all (except for the 300W for exposing Azo).

I'm wondering if there is an LED safelight that would be in the right output range for development by inspection? What is the safe range? Even with the green safelight you can only have it on for a short time, so would an LED work better if it was limited to a particular slice of the spectrum that the green filter can't entirely filter out?

Another idea would be an infrared led and a infrared spotting scope I guess, but I think a green led alone would be cheaper.

Thanks,

William

Sean · Aug 26, 2004

I'm currently building the following system and hope to use it in the near future for 8x10 dev

1 infrared nightvision monocular
1 infrared LED light source
1 glass tray

The idea is to have the IR light source under the glass tray beaming up through the film while it's being dev'd. The infrared night vision scope can watch the development. You can find the scopes on ebay and the IR light sources at reasonable prices. I plan to post an article on it when it's up and running. The scope works great too, I am able to read very fine text on a page in total darkness at a 12inch distance. So the end result should be like deving film on a light table..

philldresser · Aug 26, 2004

Sean.

We are all eagerly awaiting your results from this method.

Personally I cannot understand why you are dragging your heels. After all, you have nothing else to do

Phill

Jon King · Aug 26, 2004

wdemere said:
I've been using a red led safelight for about 6 months now in my darkroom and it is extremely bright without fogging anything. I just plugged it into the normal room light and now don't even have a white light at all (except for the 300W for exposing Azo).

I'm wondering if there is an LED safelight that would be in the right output range for development by inspection? What is the safe range? Even with the green safelight you can only have it on for a short time, so would an LED work better if it was limited to a particular slice of the spectrum that the green filter can't entirely filter out?

I'm thinking of trying the green LED approach, but I've been shooting 120 film all summer, and haven't been able to try DBI. Hopefully in a month or two.
I did enough research to find out that the wavelength of a green LED is centered at the same point as a Kodak #3 green filter, so LED's should work as well, but I have no experience on the intensity. I plan to start with a single low power (20mA) LED and go from there.

An advantage I see with the LED approach ( I use a red LED for my main safelight) is that they can be battery operated. and placed anywhere. My 'darkroom' gets converted back to a bathroom at the end of the day, so wiring and hanging lights were needed is not an option

Graeme Hird · Aug 26, 2004

jdef is on the right track with the human eye's sensitivity to green. The film is panchromatic and any colour light (in the visible spectrum) will fog the film.

The green safelight is used because it enables us to see well enough with very low light levels. You can use any colour safelight you want, or any light source including LEDs, but you must have a very small amount of light being emitted if you don't want the film fogged. You'll get the best results if you can turn the light on and off quickly without using your hands.

Sean's method has heaps of potential. I look forward to seeing how well it works.

Cheers,

john_s · Aug 26, 2004

FWIW, there is a graph somewhere that shows the wavelength of maximum sensitivity of the human eye as the intensity of light diminishes. I'll see if I can find it.

Also, the output spectrum of LEDs is wider than most would imagine. Probably not an important issue for this purpose, but a yellow filter might help cut some blue out of the green LED light. I assume that the blue would be better removed.

View the light of your LED reflected from the surface of a CD at the angle that shows the "rainbow" effect and you might be surprised to see what's there.

Christian Olivet · Aug 26, 2004

I will tell you what I have been using for the last three years. It is a little safety light that you plug on any outlet, it is green in color and it's output is a mere 4 watts although the light is very bright in the darkroom. When I develop by inspection I use a pedal to turn it on and inspect for one or two seconds, at 2 or 3 feet first but sometimes go up to 6 inches if I really need to for those extra stout negatives for Azo printing.
I got a twin pack at Kmart for about 5 dollars. I never felt the need for a better piece of equipment all thanks to Martha Stewart.

wdemere · Aug 27, 2004

Christian Olivet said:
I will tell you what I have been using for the last three years. It is a little safety light that you plug on any outlet, it is green in color and it's output is a mere 4 watts although the light is very bright in the darkroom. When I develop by inspection I use a pedal to turn it on and inspect for one or two seconds, at 2 or 3 feet first but sometimes go up to 6 inches if I really need to for those extra stout negatives for Azo printing.
I got a twin pack at Kmart for about 5 dollars. I never felt the need for a better piece of equipment all thanks to Martha Stewart.

KMart sells green safelights? Is it like a green party bulb or something? If you can give a description or a brand/part I'm on my way there now....

Did they have the footswitch too?

Thanks,

William

Thomassauerwein · Aug 27, 2004

wdemere said:
KMart sells green safelights? Is it like a green party bulb or something? If you can give a description or a brand/part I'm on my way there now....

Did they have the footswitch too?

Thanks,

William

You can get these green footswitch extension cords (for Christmas trees) there and at most hardware stores. They are around 5.00$

gainer · Aug 27, 2004

john_s said:
FWIW, there is a graph somewhere that shows the wavelength of maximum sensitivity of the human eye as the intensity of light diminishes. I'll see if I can find it.

The wavelength of peak sensitivity of the eye shifts toward blue as illumination decreases. It would be best to get a 500 nm LED than the 550 nm. Leave out the yellow filter.

gainer · Aug 27, 2004

I'm assuming that the eye will be completely dark adapted when the inspection light is turned on. In order to be sure, it would be best to use a fairly dim red light while preparing the developing trays. The red light does not interfere with the dark adptation process. Under these conditions the peak sensitivity is shifted about 50 nm toward the blue.

titrisol · Aug 27, 2004

I rememeber there was a method to desensitize panchro film for this purposes.
Pincariptol yellow was used I think to orthochormatize a panchro film

Christian Olivet · Aug 27, 2004

wdemere said:
KMart sells green safelights? Is it like a green party bulb or something? If you can give a description or a brand/part I'm on my way there now....

Did they have the footswitch too?

Thanks,

William

Some call these "Night Lights", they are the kind you plug on the outlets so when you get up at night you can see where you are walking. They are not safe lights, but maybe the should be called safety lights.

It is not a fancy solution but it worked for me so well that I am not the least interested in getting anything else.

LED safelight for Development by Inspection?

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