UV range of my Plasma plate surprisingly lots of UV

[dabateman]

I mentioned I have a plasma plate. This is a toy that I will no longer let my kids play with after this test. It is a plate which flashes color plasma discharge. It has two settings one for voice sound activation and the other for just on.

 

For these images I used the KSS Imager with KSS 60mm F3.5 lens set at F4. The only illumination in the room is from the Plasma plate, all other lights are off.

 

This is a visible image of the toy:

 

254bp25 filter, you actually see the center core of the thing (ISO 1600 F5.6 1 second):

 

303bp10 stacked with U340 2mm stacked with U330WB80improved filter to ensure No IR or visible leakage (1600, F5.6 1/2 seconds):

 

313bp25 stacked with U330WB80 improved filter (ISO 1600 F5.6, 1/4 second):

 

335bp10 stacked with U330WB80 improved filter (ISO 1600 F5.6, 1/4 seconds):

 

370bp15 stacked with U330WB80 improved filter (ISO 1600 1/15 sec F5.6):

 

390bp25 filter (ISO 400, 1/20 seconds F5.6):

 

405bp10 fitler (ISO 200, 1/20 seconds, F5.6):

[Stefano]

They work using fluorescence. The arcs (or discharges) emit UV light which lights up the fluorescent beads.

 

I don't understand why they don'use a UV-absorbing glass. Also, did you seriously see something at 254 nm? Is the glass plate actually quartz? Normal glass should be 100% opaque <300 nm or so.

[Andy Perrin]

Stefano, there's no such thing as 100% opaque...my guess is that the light is extremely bright and the glass isn't thick enough to absorb everything. Also keep in mind this is a plate geometry, not a sphere:

https://www.zzjphgoods.com/index.php?main_page=product_info&products_id=680253

 

So the source of the light is directly beneath the glass.

[dabateman]

Yes, Its a plate. These images should help:

[Stefano]

So the source of the light is directly beneath the glass.

This shouldn't make any difference, because if the gases inside do not absorb significantly the light, having the same thickness of glass near or far away from the source doesn't change the absorption.

 

Anyway, normal glass probably absorbs at least 99.9% of UVC at 2-3 mm thickness. This is just a guess.

[Andy Perrin]

This shouldn't make any difference, because if the gases inside do not absorb significantly the light, having the same thickness of glass near or far away from the source doesn't change the absorption.

Light rays aren't parallel like a laser in general, so they tend to decrease in intensity like 1/r^2 in the absence of something to focus them. Being closer to the source makes a difference.

 

Anyway, normal glass probably absorbs at least 99.9% of UVC at 2-3 mm thickness. This is just a guess.

If it's bright enough (or if you expose for long enough) it won't matter. (And that does not look like 2-3mm either.)

[Stefano]

 

Light rays aren't parallel like a laser in general, so they tend to decrease in intensity like 1/r^2 in the absence of something to focus them. Being closer to the source makes a difference.

Think about the electric field as an analogy. If you have a sphere, and some charge INSIDE the sphere (that's important), the electric field flux exiting or entering the sphere is always the same, regardless of the sphere radius (Gauss's theorem). The electric field, instead, is stronger on the surface of a smaller sphere (if you are closer to the charge). The same happens with light. The total amount of light exiting an enclosed surface ("flux") is always the same, even if the surface material absorbs that light to some extent. The intensity of the light, or the irradiance in this case, is stronger nearer the light source.

 

But from an imaging viewpoint, the distance of a filter from the light source being imaged doesn't matter. If you image a lightbulb with a filter 10 cm away or 10 m away from it, provided that you have your camera or your eyes always in the same position (farther than 10 m of course), doesn't make a difference.

[Andy Perrin]

But from an imaging viewpoint, the distance of a filter from the light source being imaged doesn't matter. If you image a lightbulb with a filter 10 cm away or 10 m away from it, provided that you have your camera or your eyes always in the same position (farther than 10 m of course), doesn't make a difference

That's ridiculous. Of course it makes a difference. At 10 meters you will see very little of the light from the bulb, because it will be like 1 pixel on your device.

 

The total amount of light exiting an enclosed surface ("flux") is always the same, even if the surface material absorbs that light to some extent. The intensity of the light, or the irradiance in this case, is stronger nearer the light source.

The flux is the amount per unit area. The total amount of light (flux * area) is constant, but the amount in any particular direction is not. Intensity includes both the flux and the solid angle, but the further away you are, the smaller the solid angle your sensor covers.

[Stefano]

 

That's ridiculous. Of course it makes a difference. At 10 meters you will see very little of the light from the bulb, because it will be like 1 pixel on your device.

I didn't explain it well. In both cases you are standing at the same distance from the lightbulb, ex. 15 m. You and the lightbulb don't move. First, put a filter (ND, blue, etc.) 10 cm away from your lightbulb, between you and the lightbulb, so that you see the lightbulb through the filter (the filter must be big enough to cover the entire lightbulb from your perspective). If you put the filter 10 m away from the lightbulb, you see the lightbulb the same as before.

[Andy Perrin]

Yes, it doesn't matter where the filter is between you and the bulb, but that was never my point. The point is that in a sphere, the discharge might be 10cm from the glass (and most of the light is going off sideways somewhere ) whereas in a disk it's right next to the glass and most of it is leaving straight ahead. Anyway, not sure how much difference it makes since it's only a few cm either way.

[Andrea B.]

Well, I think I followed some of that. :lol:

 

Dave, the images are nifty doodle for sure !! Thanks for posting.

[dabateman]

Every "normal" kid who plays with it always sticks tieir eye ball right up to the center and looks right at that UVC emitting core.

 

So it went back to from whence it came. It was on loan anyway. So hopefully a more needy child is benefiting from it.