UV dye bleaching

I've read that UV light can bleach organic dyes if applied in strong quantities. However, I don't know what wavelengths are appropriate for this kind of bleaching. There are UV-A (400-315nm), -B (315-280nm), and -C (280-100nm) sources for UV light but which is most effective in general? Could it even be done (effectively) with a 405nm violet laser?

If anybody knows, can you please chime in on this subject.

C is likely the best, followed by B, followed by A. 405 is too long of a wavelength to be able to do it reliably.

Yes, lower wave length is likely best.
However you are likely to need a lot of watts, and will have to consider what you can get at a reasonable price.
Remember to cover up your light box, it is not good for the eyes.

Hmm, that's not too bad then. I think those UV fluorescent light bulbs (i.e. without any phosphorescent material on the outside) are relatively cheap.

Definitely want the light box for the cancer bulb.

Bionic-Badger said:

Hmm, that's not too bad then. I think those UV fluorescent light bulbs (i.e. without any phosphorescent material on the outside) are relatively cheap.

Definitely want the light box for the cancer bulb.

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Not to mention a nasty UV burn or sun burn.

Bionic-Badger said:

Hmm, that's not too bad then. I think those UV fluorescent light bulbs (i.e. without any phosphorescent material on the outside) are relatively cheap.

Definitely want the light box for the cancer bulb.

Click to expand...

Those germicidal bulbs arent expensive indeed - i think the lamps are in the order of $15 each (for an 8 watt), and the ballast is the same as you use for normal fluorescents. The extra price for the bulbs compared to normal onces is due to the envelope being made out of quartz glass so that it passes UVC well - the output is around 250 nm.

We had them in hoods for microbiological work, on timers such that they would burn for an hour somewhere at night, killing any cells left in the hood. I never noticed bleaching of stuff left under them though, but since you were supposed to leave these hoods empty it didnt happen very often.

They're just unfiltered low-pressure mercury lamps, so all mercury lines show through. The light appears to the eye as a light blue:

Thanks for the advice guys! I've purchased a hanging fluorescent light and one of those germicidal bulbs. I'll see how it goes.

The light looks blue indeed - its the full mercury spectrum that comes out. The normal glass from those working hoods blocks most of it, though looking at it when on is still advised against.

What exactly are you trying to bleach?

I'm seeing if I can bleach out the bayer filters in digital cameras. It'd essentially give me a black and white camera, but at full resolution via the RAW output, which is quite a bit sharper than the normal weighted black and white output.

I've read that others have tried it without success, but I don't know the conditions in which they were attempting it. If they were trying to bleach the filters through the front of the camera it may not have been very effective with all that glass and the IR/UV cut filters. I'll be testing it on some cheapie webcam with the lens removed, and then on a digital camera I have that I've removed the IR/UV cut filter from (exposing it to UV without a lens as well).

Oic.. so you put the whole sensor chip including its filter under UV light in an attemp to bleach out the filter pigments?

Its an interesting idea for sure, but somehow i doubt there is a level of exposure that will bleach out the filter but leave the sensor functional. I've never noticed degradation in the filters under normal use, even taking many photos under the desert sun - so i doubt the filters are very prone to photodegradation at all.

I do think the silicon will hold up, but I don't know about any other plastics that could be on the sensor, especially on the webcam. While it is suggested not to expose the sensors to the sun because of color degradation, the main source of sensor damage is focused heat, not UV. I'll have to find a way to block out any heat from that bulb or other sources.

People have reported color degradation over time when filming sunsets with the "shutter" wide open; a "path" of color degradation would appear where the sun had passed over. I expect this was on a webcam that recorded the sky over longer periods. From this I have some hope that I'll be able to bleach the Bayer filter especially since webcams use plastic lenses instead of optical glass (opaque past 310nm), and are usually uncoated.

Still, that was the sun, focused, over hours a day, so I may have some time to spend bleaching this with the germicidal lamp. The germicidal lamp puts out UV-C, which is blocked by optical glass, and little UV-C makes it through the atmosphere. How those organic dyes might react to it I'm not sure. Worth a shot though.

Man, are you sure they are not dichroic coatings, but are really organic?

I would think what you are seeing is storing extra free electrons in the silicon. Very much like the stored charge in a ram or eeprom chip. It only takes about 400,000 electrons to saturate a pixel in many CCDs. Get some charge in the wrong place with the chip under bias and it might be there for a while.

If your trying to degrade a organic, you might wish to be in the 254 nm range. Or find a polymer testing lab with a "weatherometer" machine with the xenon long arcs.

Steve

Bionic-Badger said:

People have reported color degradation over time when filming sunsets with the "shutter" wide open; a "path" of color degradation would appear where the sun had passed over. I expect this was on a webcam that recorded the sky over longer periods.

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I see.. never heard of this problem before, but it could be similar to burn in on a screen that displays the same image continoulsy (even some lcds are prone to that if its extreme).

It could be an entirely thermal thing though, taking photos of the sun directly is often advised against by manufacturers. You can take photos of the sunset, but taking one of the sun at noon in summer is quite likely to cause damage. I've seen many photos taken with cameras that suffered laser damage, even from exposure levels that don't exceed direct maximal sunlight.

As for the bayer filter: they use dyes. There is some development for dichroic filters as well as microlenses, but afaik none of those made it into budget cameras yet. I've heard of people physically scraping the filter off the sensor, though i doubt thats a very safe approach either

I'm not sure what the mechanism was behind the color degradation people described in their cameras. I've blasted webcams with lasers and they definitely maintain a charge on the CCD that doesn't go away until reinitialized (no autoexposure settings, etc. fix it), but not a color degradation, and not in the path of the beam either. An extremely bright source usually blooms and bleeds into other columns, not leaving a distinct trail.

For scraping, I've seen the results of Bayer scraping on cheapo cameras, but am pretty reluctant to take a knife to the sensor of a more expensive camera, even if only because it may not work at all.

Some folk have used strong UV sources on the arrays, but they may have been attenuated by the glass or the filters inside, especially UV-C which won't even go through the glass. I bought a fluorescent lamp, and a germicidal bulb, so I should be able to produce UV-C in decent quantities. I also purchased a (backordered) high powered 365nm LED that I'll be trying out on it, to get some "pure" UV light sources, but the UV-C would probably be more effective.

I'll see how it goes. I've got all the parts ordered, and a candidate handheld digital camera to try it with once I've tested out the webcams.

Its just a matter of trial and error then - just let it bake under the germicidal bulb for a day and see if anything happens. If the light from that bulb wont bleach it out, nothing will.

Just be darn careful with that lamp though - its a proper cancer-ray alright