Strange behavior of lamps and glass

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FarbigeWelt
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Re: Strange behavior of lamps and glass

Post by FarbigeWelt » Mon Mar 25, 2019 7:44 am

CodeHD wrote:
Sun Mar 17, 2019 6:18 pm
In practice, it is not always obvious which component dominates.
I really like your and B.Y.O.B answer too. Perfect glass is almost invisible. No absorption, no reflections, IOR only. But perfect glass is like a platonian body, very nice but not real.

The fluorescence does not apply in LuxCoreRender because it renders in visible spectrum only. I guess excitation wavelength is below visible range even if emission wl is visible.

Imagine a fiber glass. Forget about the IOR gradient. If the fiber was not as clean as it is you could not transmit digital signals over kilometers of length. This glass is as clear as technically possible to reasonable prices. Window glass is green or yeloow if you look at through a few decimeters.
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Re: Strange behavior of lamps and glass

Post by CodeHD » Mon Mar 25, 2019 11:49 am

FarbigeWelt wrote:
Mon Mar 25, 2019 7:44 am
no reflections, IOR only.
Maybe just to clarify this statement for those not so deep into the subject: There is a reflection from perfect glass, too, the Fresnel reflections due to the IOR.
FarbigeWelt wrote:
Mon Mar 25, 2019 7:44 am
The fluorescence does not apply in LuxCoreRender because it renders in visible spectrum only. I guess excitation wavelength is below visible range even if emission wl is visible.

Imagine a fiber glass. Forget about the IOR gradient. If the fiber was not as clean as it is you could not transmit digital signals over kilometers of length. This glass is as clear as technically possible to reasonable prices. Window glass is green or yeloow if you look at through a few decimeters.
I do admit I don't really know about the absolute amounts of fluorescence. It varies quite a lot from glass-type to glass type. But excitation also happens with visible wavelengths. There is a nice technical note from Schott, if you are interested. Unfortunately, it gives relative fluorescence.

https://www.us.schott.com/d/advanced_op ... ass_us.pdf

I have some cheap achromatic lenses lying around where one component shows quite strong fluorescence with a violet laser. Unfortunately I don't know the glass type of it. I will try to remember to test it with blue LED lights in the evening, if I can make it visible.

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Re: Strange behavior of lamps and glass

Post by FarbigeWelt » Mon Mar 25, 2019 2:49 pm

CodeHD wrote:
Mon Mar 25, 2019 11:49 am

https://www.us.schott.com/d/advanced_op ... ass_us.pdf

I will try to remember to test it with blue LED lights in the evening, if I can make it visible.
Very interesting information. Indeed one can observe emission based on visible excitation. Blue LED should do the trick.
As much I understood the article, in the short time reding, emission due to excitation around 535 nm should be rather faint in optical degree glasses. But a good crystal wine glass may shine in blue LED light with about 430 nm.

The data sheets Schott optical grade glasses:
https://www.schott.com/d/advanced_optic ... 012017.pdf

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Re: Strange behavior of lamps and glass

Post by CodeHD » Mon Mar 25, 2019 10:27 pm

FarbigeWelt wrote:
Mon Mar 25, 2019 2:49 pm
Very interesting information. Indeed one can observe emission based on visible excitation. Blue LED should do the trick.
As much I understood the article, in the short time reding, emission due to excitation around 535 nm should be rather faint in optical degree glasses. But a good crystal wine glass may shine in blue LED light with about 430 nm.
Well, it is stuff like this that really gets me started, so naturally I have done it immediately... :D

Test setup consists of:
- A wine glas (Not good old crystal, but at least I had some new and unused ones, so no wine stains affecting the result)
- An achromatic lens, made of two unknown glass types (OPTI*Media achromat 2-lens, f=280,1mm for anyone interested)
- A white LED room light
- Blue LED light from a fixture mounted above, illuminating a large part of the room.
- A Laserpointer with 405 +- 10 nm (according to the label, but it is one of these cheap ones that should really be forbidden, so who knows)
- A black background, but the rest of the room is a normal lving room, so expect visible reflections on the glass

First, an image of the wine glass under white LED light for reference:
Glas_Fluoro_01.JPG
Second, the wine glass under blue LED light:
Glas_Fluoro_08.JPG
No fluorescence is visible. Reflections from the background are quite dominant, so this would have to be done in a large, black room with directed light, which I can't set up quite so easily.

Next, placing the lens beside it:
Glas_Fluoro_03.JPG
Again, nothing visible immediately, so lets add a laser:
Glas_Fluoro_04.JPG
Now we can see something, lets get a closer look:
Glas_Fluoro_05.JPG
We can see that one component produces strong, green fluorescence, the other maybe scatters? Lets get a cross-section profile:
fluoroAnaLabeled.png
It actually seems more like fluorescence with red emission rather than green. Maybe some scatter in addition, hard to say without a spectrometer.

Lets take a look at the wine glass again, shining the laser through the handle:
Glas_Fluoro_06.JPG
Now the wine glass also shows green fluorescence. You can't see this in the top-part of the glass (where you pour the wine in), because the glass is too thin and you only see the spot on the surface.
I tried also with green and red lasers, I only get some scatter with them.

And lastly, you can use this to create some nice effects in the foot:
Glas_Fluoro_07.JPG
(Note that the laser was mounted in place, so the streaks are not from my hand shaking, that is the uneven surface of the glass!)

So I would conclude: Fluorescence is indeed negliglible, unless you want to render some very specific situations, possibly involving lasers.

P.S.: Sorry for going a bit off-topic again :roll:

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Re: Strange behavior of lamps and glass

Post by FarbigeWelt » Tue Mar 26, 2019 7:50 am

CodeHD wrote:
Mon Mar 25, 2019 10:27 pm
P.S.: Sorry for going a bit off-topic again
I disagree, this has a lot to do with visibility of glasses.

And you made a very nice and reasonable experiments. If thete were a large dark room one could see only laser is bright enough to make even not perfect glass visible due to intense dispersion and some faint fluorescence.

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