Building LED safelights?

[Tom Kershaw]

Brilliant! If my breadboard will ever have to vacate the top of the water tank I might just steal that housing solution from you!!

I will report back again once I have an impression of how "safe" the light is. My visual perception is that the LEDs are producing a fairly monochromatic output, in accordance with the specified 590nm, although I don't have a tool to measure this.

 

[koraks]

My visual perception is that the LEDs are producing a fairly monochromatic output, in accordance with the specified 590nm, although I don't have a tool to measure this.

Did you check with a cd/dvd? It gives a good impression of any spectral impurities, although it only does so qualitatively - i.e. it does show if the leds emit other colors than the ones they are specified for, but it's hard (impossible) to tell how much of that undesirable light is present exactly. It's a good starting point for trouble shooting though.

 

[Tom Kershaw]

Did you check with a cd/dvd? It gives a good impression of any spectral impurities, although it only does so qualitatively - i.e. it does show if the leds emit other colors than the ones they are specified for, but it's hard (impossible) to tell how much of that undesirable light is present exactly. It's a good starting point for trouble shooting though.

Yes, I've just done this and do see some green unfortunately. Perhaps I should go and order some red LEDs for comparative purposes.

 

[Tom Kershaw]

Safelight test results (16 amber LEDs):

• ILFOBROM GALERIE - test to 6 minutes exposure time, completely safe.
  
• ILFORD MG WARMTONE - test to 6 minutes exposure time, completely unsafe.

I think this is down to the spectral sensitivity of the paper as GALERIE seems to only be sensitive to near blue. I will test with red LEDs when these arrive.

A note on illumination levels: 16 LEDs is very bright, and I suspect 12 may be more than sufficient, I've re-worked my experimental unit with 8 lights and this is okay but slightly dim.

 

[Tom Kershaw]

So today I have tested an arrangement of eight red LEDs in the centre fitting and four red LEDs off in a corner (battery powered). This passes safe for ILFORD MG WARMTONE.

 

[Danner]

I'm using red LED light bulbs I got off Amazon. No fog issues, but I don't leave paper lying around. The key is to buy LED bulbs made with red LEDs, and not LED bulbs made with white LED's with a red globe around them, because, red LEDs are monochromatic.

 

[koraks]

red LEDs are monochromatic.

Yes. Sort of. But not quite. And that's why it's necessary to test.

 

[distributed]

Yes. Sort of. But not quite. And that's why it's necessary to test.[/qoute]

Fully agree. @Danner I have fogging on Foma RC paper with red LEDs, not with LEDs covered with filters.

 

[Danner]

Red LED's, most commonly employing GaAsP semiconductor materials, emit light in the 630-660 nm range. Ilford MGIV RC paper sensitivity ranges from about 375nm to 550nm, so the 630nm LED is significantly above that range. I suppose with extended exposure there may be some fogging, but it shouldn't be a problems with careful handling, IMHO.

 

[koraks]

@michael_r is right. Of course, in a perfect world, GaAsP would be 100% GaAsP. In reality, it may be 99.95% GaAsP and .05% other stuff. That's likely where the trouble starts.

 

[Tom Kershaw]

For example some people have noticed that even with relatively narrow band red LEDs peaking anywhere between 620nm and 660nm,

When I double checked my red LEDs that passed safe for Multigrade warmtone - the CD spectrum test showed some green. I have now put the set of 8 red LEDs back inside my original safelight housing to mitigate the 'green' output. I suspect if only considering Ilfobrom Galerie papers, one could print in a very pleasant and bright amber lit darkroom.

 

[Tom Kershaw]

graded papers are basically blue-sensitive emulsions typically with comparatively little sensitivity into the green spectrum

I have good stocks of paper at the moment but I'm unsure as to the current status of GALERIE paper within the ILFORD portfolio. Many lines are showing as out-of-stock on the UK direct sales website - however this option tends to be more expensive than traditional dealers and doesn't always show the full range.

Fomabrom appears to have greater 'green' sensitivity than Galerie:

https://www.foma.cz/en/fomabrom (to about 540nm)

https://www.ilfordphoto.com/amfile/file/download/file/1741/product/722/ (to 500nm)

 

[DWThomas]

My attempts to use a red LED bulb with Fuji green sensitive X-ray film wound up with a Rubylith filter to avoid fog, as well as a homemade neutral density filter in order to get a reasonable working time for tray development. This was an E27-R8-G from SuperBrightLeds.com --and bought several years back. Since they are apparently targeted for use on signs, one might also wonder how reliable the spectral distribution is for batches made over longer time periods.

 

[Tom Kershaw]

Since they are apparently targeted for use on signs, one might also wonder how reliable the spectral distribution is for batches made over longer time periods.

I suspect one of the lessons here is to approach LED datasheets with a degree of scepticism. The 8 LEDs within my ILFORD 902 filter set-up are rather dark and I intend to up the LED count to at least 12. I would be interested to know what results those who are using unfiltered LEDs are achieving.

 

[koraks]

My attempts to use a red LED bulb with Fuji green sensitive X-ray film wound up with a Rubylith filter to avoid fog,

Same here. Two layers of rubylith, in fact, in my case. But granted, it works very well this way.

 

[koraks]

It's still better than using an incandescent light source in the sense that the filter is doing less "work", which means it should last significantly longer.

The extended lifetime of the filter will be mostly because it probably won't get as warm as with an incandescent bulb. A filter doing 'work' isn't really degrading it significantly, except if it has to deal with a lot of UV light, which tends to break down filter dyes. This of course is by definition not much of an issue with incandescent sources (heat, however, very much is!)
Nevertheless, of course, filters will appear more effective if the light source already emits less in the undesirable parts of the spectrum. The reason for this is that filters don't block, but attenuate. This is a problem that seems to pop up once in a while when people think (and discuss) about filtration, UV blockage etc. They tend to simply the function of a filtering medium as something that blocks or does not block certain frequencies in a binary way. In reality, there's no such thing as a perfect filter - so instead of thinking about blocking, think in terms of attenuation, and everything becomes more logical all of a sudden.

 

[koraks]

Hi Koraks, what I mean by filter "work" is simply that it needs to absorb less radiation - all typical filters using dyes (as opposed to dichroic/interference) work by absorption, which is largely what causes them to degrade.

Visible light is rather low energy and doesn't easily break the carbon bonds in dyes. It won't contribute much at all to filter degradation as a result. The story is different for UV.

 

[koraks]

You're welcome - and I apologize for being rather pedantic

 

[M Carter]

Many people in the US are using these cheap red LED bulbs - they fit in any standard lamp socket, and their spectrum doesn't overlap (the spectrums are on the web page). I have 3 to 5 going at any one time, they're fantastic.

 

[Danner]

Many people in the US are using these cheap red LED bulbs - they fit in any standard lamp socket, and their spectrum doesn't overlap (the spectrums are on the web page). I have 3 to 5 going at any one time, they're fantastic.

Thanks for that, I just ordered 5 of them. [beerclink]

 

[Donald Qualls]

I haven't tested them yet, but that seller (SuperBrightLEDs) also has an amber bulb that has its peak at 590nm -- it's been confirmed by other users here to be safe on most VC and graded papers (though I wouldn't trust it on ortho films). I have hopes for it, at suitable levels of attentuation, to be a viable RA-4 safelight as well, given it's within a few nanometers of the same wavelength as the low pressure sodium lamps of Thomas and Duka safelights.

 

[M Carter]

I haven't tested them yet, but that seller (SuperBrightLEDs) also has an amber bulb that has its peak at 590nm -- it's been confirmed by other users here to be safe on most VC and graded papers (though I wouldn't trust it on ortho films). I have hopes for it, at suitable levels of attentuation, to be a viable RA-4 safelight as well, given it's within a few nanometers of the same wavelength as the low pressure sodium lamps of Thomas and Duka safelights.

Just go with the red and you're good for papers and for ortho film (I don't know of any papers that can't do red, I suppose there could be some?) Ilford's ortho can fog with too much safelight, ortho litho is very resistant though.

My darkroom is like "noon on Mars" or something, it's spectacular when you drop a pencil or dodging tool and you can actually see the damn thing! Fabulous for lith printing.

 

[urnem57]

+1 for The Red Superbright LED bulbs. I read about them on here, bought a few and am pleased with them. I never would have found them on my own.

 

[Tom Kershaw]

+1 for The Red Superbright LED bulbs. I

Unfortunately this product doesn't seem to be available on the UK / European market. I've not had a chance yet to re-build my safelight with the extra LEDs but should do soon.

 

[Donald Qualls]

Just go with the red and you're good for papers and for ortho film (I don't know of any papers that can't do red, I suppose there could be some?)

All well and good, but red safelight will produce a cyan fog on RA-4 materials. I'm perfectly okay with dim for color, but I'd really rather not work in total darkness if I can get even "not bang my head on the enlarger head" levels of safelight for that task. And the amber is much more comfortable for B&W printing as well. I do have an old red bulb safelight, so I can still use that for ortho materials like Harman Direct Positive.