IR LED Output for Infrared in the Darkroom

[Fragomeni]

Hi all. I'm building a pair of IR goggles to be used in the darkroom. My intention here isn't to start another back and forth of why people do this, if it works, or whether or not it is necessary. People do it because they want to and it brings flexibility to their process, it does work and I've seen it in practice along with densitometer measurments showing that it had no effect on exposing film, and although it may not be completely necessary I'm going to do it anyway. That should answer all of those questions so we don't have to go off topic. Anyway, my question deals with the output of commonly available IR LEDs. Modern panchromatic film becomes insensitive around 640-700nm. I want to make sure I use IR LEDs that are well outside of the sensitivity range of the film. I have some that I bought from RadioShack that are marked as having an output of 940nm. How far is that into the IR spectrum? Where does near-IR end and true IR begin? Basically, I just want to make sure that these are true IR and wont have the near-IR red glow that will effect film because it's still in the visual spectrum. Yes, I know i can just turn them on and look at them but I'd like input on the numbers in addition to a visual determination sinse I know a lot of people here have done this. Thanks for the help!

[Jim Michael]

Maybe the starting point would be to look at the spectral response plot (http://ilfordphoto.com/Webfiles/20114271120582708.pdf) for infrared B&W film, which for the Ilford film falls off to 0 a little less that 800nm. Then I'd overlay the output spectra plot for the 940nm source to verify it doesn't bleed into the sensitive range. If not then you should be safe processing even IR film by inspection. I don't know how much trust I would place in LEDs sourced from RS for accuracy of the output among samples. Might be good, might not. Maybe check the LED manufacturers for specific part IDs and then source those from some place like DigiKey.

[Fragomeni]

Good points. I forgot to mention that I don't really trust the RadioShack brand although I'm sure its fine and the labeling probably isn't too far off. I was going to ask for recomendations of good sources of high quality IR LEDs with possibily a higher nm output. I'll check out DigiKey and see if they carry something better.

[Leigh]

RTFM

Manufacturers publish data sheets with this information. Read them instead of bothering us.

- Leigh

[Fragomeni]

Looks like the highest output IR LED that DigiKey offers is 950nm. I'm wondering if I can find soem somewhere around 1060nm. I've heard of these on the market but haven't found a source yet.

[jp]

I have liked Jameco.com as well for ordering electronic parts.

An IR filter (or black used e6 film) could also be used to eliminate any visible light byproducts from near-IR LEDs.

[Fragomeni]

Leigh, I am askig the question to receive responses from people who have done what I am doing. If you know of a data sheet that directly answers my question exactly please refernce it so that I may find it because I have not seen it. Otherwise please keep ignornat, antagonistic, and entirely unhelpful responses out of the conversation. This is a community forum intended to be used for open discussion. Posting a question often results in far more information being provided then the OP intended to receive. If you don't want to be a constructive part of a conversation, stop policing the forum for posts that "bother" you and go find something better to do. The audacity of some people is mind blowing.

[Fragomeni]

jp498, thanks for the Jameco.com reference. I'll check them out to see what they have. I may actaully be able to get the E6 IR equipment from a local lab that closed but I'm making the goggles in case I can't get them.

[Leigh]

If you know of a data sheet that directly answers my question exactly please refernce it so that I may find it because I have not seen it. Otherwise please keep ignornat, antagonistic, and entirely unhelpful responses out of the conversation.
If you go to any real electronics parts distributor site, one of the selection criteria for IR LEDs is wavelength. The longest I've seen is 950nm.

LEDs are highly monochromatic, having a very narrow emission band, quite unlike thermal emitters If you buy a 950nm emitter, you don't get energy at 940nm. As far as posting a link to a datasheet, all of the online distributors provide links for each individual product. There are hundreds of them.

Distributors:
Mouser www.mouser.com
Newark www.newark.com
Allied www.alliedelec.com
Digi-Key www.digikey.com

IR illumination systems are readily available, used for surveillance cameras and backup cameras for vehicles. Why not just buy one of those?


The audacity of some people is mind blowing.
Yep. The audacity of those who are too lazy to do their own research is certainly mind blowing.

- Leigh

[Fragomeni]

Thanks for the link Leigh. I'll look through them. As to the last bit, it doesn't look like anyone else had any problems weighing in with useful information relevant to the original post. Interesting how that happens. If I didn't do any leg work, I probably wouldn't have any of the numbers that are in the original post. I think most people here understand the point of asking questions; to gain further information relevant to whats being worked on. If I'd found everything I needed in data sheets I probably wouldn't have needed to post a question. Seeing as how I now have new sources recommended and good thinking points offered by contributors, all of which will be a resouce for people who read this thread in the future, I feel like the thread was pretty successful. Cheers.

[Bill Burk]

Hi Francesco,

How are your eyes going to detect infrared through welders goggles? That's just a facemask with heavy glass plates over your eyes, right?

I would not recommend you to use so much infrared illumination that your eyes can detect the light. It sounds like it would expose the film.

I bought one of each of the RadioShack IR LED's. They are all real infrared. But none of them provide "light" that is near enough to visible to act like darkroom lights for my Viper. I can see spots of light, so I know they are "on" but they don't light things up.

I use the ATN Viper night vision goggle. It isn't a "camera" but a system that amplifies the light by exciting a green phosphor screen. It's Generation 1 amplification, nothing like the expensive military or police spec gadgets that can spot the heat signature of an escaping suspect.

The LED on my ATN Viper floods the darkroom (as far as the Viper is concerned) while emitting a dim glow of red. I can put 5 or 6 black 35mm slides over it and still can see the dim glow of red undiminished. So I know my eye is seeing that infrared and it scares me to think how much is hitting my eye. So I avoid looking at it.

[Fragomeni]

Hi Francesco,

How are your eyes going to detect infrared through welders goggles? That's just a facemask with heavy glass plates over your eyes, right?

I would not recommend you to use so much infrared illumination that your eyes can detect the light. It sounds like it would expose the film.

I bought one of each of the RadioShack IR LED's. They are all real infrared. But none of them provide "light" that is near enough to visible to act like darkroom lights for my Viper. I can see spots of light, so I know they are "on" but they don't light things up.

I use the ATN Viper night vision goggle. It isn't a "camera" but a system that amplifies the light by exciting a green phosphor screen. It's Generation 1 amplification, nothing like the expensive military or police spec gadgets that can spot the heat signature of an escaping suspect.

The LED on my ATN Viper floods the darkroom (as far as the Viper is concerned) while emitting a dim glow of red. I can put 5 or 6 black 35mm slides over it and still can see the dim glow of red undiminished. So I know my eye is seeing that infrared and it scares me to think how much is hitting my eye. So I avoid looking at it.
Hi Bill,
You're absolutely right. Thats what we were talking about in the other thread; the simple fact that human eyes cannot see infrared light by themselves, filters or no filters. I clarified with my friend (the one who put all of this in my mind) what he was working with and the experiments he has done. I was mistaken on a few of the things that he's explained to me in regard to the goggles that he made. He did make goggles that see infrared but because they have no intensifier all you can see is the glow of the IR LED and the glow is not enough to illuminate anything. The infrared goggles with the intensifier technology is what I'll be using. I purchased a promising set from B&H and will give them a go when they arrive.

[ryan_lydon]

I made a light box with the 5mm infrared LEDs available from radioshack and use them in conjunction with a pair of toy infrared goggles so that I can develop my sheet film by inspection. Works great, no noticeable fog. I am using Tri-x and I checked the spec page vs the specs on the back of the package of the LEDs. I did, however, have to use some black leather to make a headband for the goggles to make sure that the viewing light was completely blocked out. And I had to block out a couple of other external light leaks on the goggles. My goggles are Eyeclops, I didn't buy them, I borrowed them from a friend, as I doubt I would have dropped a hundred bucks on something that might work. They work way better than I thought they would. I only used to leds for my lightbox (it is approx 5x7 and four inches deep). If I remade it I would use at least six. It is a beautiful thing to watch the neg develop in front of your eyes. I use a couple of trays of rodinal in various dilutions along with a water tray.

[ryan_lydon]

Two, not to, too. I should really proofread better.

[domaz]

BG Micro has a whole bank of IR illuminators (http://www.bgmicro.com/LED1153.aspx) already assembled. Could be a good shortcut to soldering a bunch of loose LEDs

[jeroldharter]

I was worried about the red glow of the ATN Viper fogging film. I never saw any evidence of it, nor did I specifically test for it. I figured that if I could see it I was running the risk of fogging the film. I taped over the emitter to blacken the red light and bought some tiny IR rescue beacons to use as IR safe lights. That works ok but is dimmer than the big red glow.