Help reversing thorium oxide on my lens.

stevebrot · 07-11-2018, 09:38 PM

Originally posted by Bob 256

It takes the high energy of UV light to reverse this process (bleach it).

Are you saying that those of us having success with a high-intensity non-UV JANSJÖ desk lamp are mistaken?

Steve

Last edited by stevebrot; 07-11-2018 at 10:43 PM.

leekil · 07-11-2018, 10:24 PM

Originally posted by stevebrot

Are you saying that those of us having success with a high-intensity non-UV desk lamp are mistaken?

Do those lamps emit *only* non-UV light?

stevebrot · 07-11-2018, 10:42 PM

Originally posted by leekil

Do those lamps emit *only* non-UV light?

Good question. I am confident that mine is not a high energy UV source and that I don't need sunscreen or protective eye wear when using it for reading. I could not find the references, but do remember reading that there is little, if any UV or near UV in the JANSJÖ's emission spectrum.

Steve

**Bob 256** · 07-12-2018, 07:42 AM - **1 Like**

Originally posted by stevebrot

Are you saying that those of us having success with a high-intensity non-UV JANSJÖ desk lamp are mistaken?

Steve

I didn't say that at all if you re-read my post. I said that UV is more effective because of its higher energy (compared to visible light). It's possible that your desk lamp may emit some UV or near-UV light in its spectrum (particularly if its an LED type lamp, many of which use a near-UV pump source for their production of white light).

In any case, I'm not making ANY statements that you are mistaken. If it works, it works.

Last edited by Bob 256; 07-12-2018 at 07:47 AM.

stevebrot · 07-12-2018, 12:47 PM - **1 Like**

Originally posted by Bob 256

I didn't say that at all if you re-read my post. I said that UV is more effective because of its higher energy (compared to visible light). It's possible that your desk lamp may emit some UV or near-UV light in its spectrum (particularly if its an LED type lamp, many of which use a near-UV pump source for their production of white light).

In any case, I'm not making ANY statements that you are mistaken. If it works, it works.

I reread the post and the previous one above it. Your conclusion to the second was succinct and what I quoted above:

Originally posted by Bob 256

It takes the high energy of UV light to reverse this process (bleach it).

That is conventional wisdom and one with which I have generally agreed. When I first read of people using the inexpensive JANSJÖ lamp, I shook my head and rolled my eyes. My thoughts were, "Right...that little lamp has more umph at the UV end than enough hours in full sun to do permanent damage to living things? No way...". However, I have an IKEA less than 15 miles from my home and the cost was less than $10. Having been unable to clear my lens using solar power and having no access to UV lamps, I figured the biggest risk is that the JANSJÖ might not work well as a desk lamp should the decolorizing not work.

Paradoxically, the JANSJÖ did work and with no collateral damage to the wood tabletop a few millimeters from the light's face. The lens was cleared and the table top was still deep red stained. To play it safe I did place foil to protect for the next several decolorings, but I doubt it was needed. I have not dived very deep into the spectral or energy curves for the lamp, but I do know that those doing macro and near-micro photography have showed intense interest in this easily-placed and very bright white (reportedly 3250K* (CCT)) light source. It is possible that some of those people, particularly the stamp and coin photographers might have more detailed spectral breakdown. I personally doubt that much of the power curve is much beyond 400nm, though it is hard to say. My suspicions are that the required spectral component might be at longer than UV wavelengths.

I echo your sentiments...if it works, it works...

FWIW, the JANSJÖ is sort of meh as a desk lamp.

Steve

* My estimate using CT correction with my K-3 is 3200K.

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07-11-2018, 09:38 PM	#46
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Bob 256 It takes the high energy of UV light to reverse this process (bleach it). Are you saying that those of us having success with a high-intensity non-UV JANSJÖ desk lamp are mistaken? Steve Last edited by stevebrot; 07-11-2018 at 10:43 PM.

07-11-2018, 10:24 PM	#47
leekil Pentaxian Join Date: May 2016 Photos: Albums Posts: 2,003	Originally posted by stevebrot Are you saying that those of us having success with a high-intensity non-UV desk lamp are mistaken? Do those lamps emit only non-UV light?

07-11-2018, 10:42 PM	#48
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by leekil Do those lamps emit only non-UV light? Good question. I am confident that mine is not a high energy UV source and that I don't need sunscreen or protective eye wear when using it for reading. I could not find the references, but do remember reading that there is little, if any UV or near UV in the JANSJÖ's emission spectrum. Steve

07-12-2018, 07:42 AM - 1 Like	#49
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,379	Originally posted by stevebrot Are you saying that those of us having success with a high-intensity non-UV JANSJÖ desk lamp are mistaken? Steve I didn't say that at all if you re-read my post. I said that UV is more effective because of its higher energy (compared to visible light). It's possible that your desk lamp may emit some UV or near-UV light in its spectrum (particularly if its an LED type lamp, many of which use a near-UV pump source for their production of white light). In any case, I'm not making ANY statements that you are mistaken. If it works, it works. Last edited by Bob 256; 07-12-2018 at 07:47 AM.

07-12-2018, 12:47 PM - 1 Like	#50
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Bob 256 I didn't say that at all if you re-read my post. I said that UV is more effective because of its higher energy (compared to visible light). It's possible that your desk lamp may emit some UV or near-UV light in its spectrum (particularly if its an LED type lamp, many of which use a near-UV pump source for their production of white light). In any case, I'm not making ANY statements that you are mistaken. If it works, it works. I reread the post and the previous one above it. Your conclusion to the second was succinct and what I quoted above: Originally posted by Bob 256 It takes the high energy of UV light to reverse this process (bleach it). That is conventional wisdom and one with which I have generally agreed. When I first read of people using the inexpensive JANSJÖ lamp, I shook my head and rolled my eyes. My thoughts were, "Right...that little lamp has more umph at the UV end than enough hours in full sun to do permanent damage to living things? No way...". However, I have an IKEA less than 15 miles from my home and the cost was less than $10. Having been unable to clear my lens using solar power and having no access to UV lamps, I figured the biggest risk is that the JANSJÖ might not work well as a desk lamp should the decolorizing not work. Paradoxically, the JANSJÖ did work and with no collateral damage to the wood tabletop a few millimeters from the light's face. The lens was cleared and the table top was still deep red stained. To play it safe I did place foil to protect for the next several decolorings, but I doubt it was needed. I have not dived very deep into the spectral or energy curves for the lamp, but I do know that those doing macro and near-micro photography have showed intense interest in this easily-placed and very bright white (reportedly 3250K* (CCT)) light source. It is possible that some of those people, particularly the stamp and coin photographers might have more detailed spectral breakdown. I personally doubt that much of the power curve is much beyond 400nm, though it is hard to say. My suspicions are that the required spectral component might be at longer than UV wavelengths. I echo your sentiments...if it works, it works... FWIW, the JANSJÖ is sort of meh as a desk lamp. Steve * My estimate using CT correction with my K-3 is 3200K.