I don't know how to check if it is glass or plastic, but it looks glass.
I can't take the head apart for closer inspection, since it's glued to the body.
Is it glued with yours also?
Knock on it with something metallic, a knife perhaps. You cannot fail to assess the sound of glass vs plastic if properly knocked on it.
It sounds glass, but the sound is dampened by its being fixed in the flashlight's head.
Maybe there's an o-ring there?
Anyway, it sounds midway between glass and plastic.
Then a needle test. Glass sould not let the needle stuck by pushing it on the lens. Try on the edge (to avoid having some visible damage) if you're not concerned knowing you have a 0,3mm hole in the plastic lens somewhere.
First it looked like plastic because of some very small scratches, but maybe it is coated glass, I noticed that reflected light shimmers somewhat on the surface. It is specified as "Toughened ultra clear glass lens with AR coating" on the Tank007 site, but I don't trust these specifications very much. I wouldn't try with a needle...
I didn't try to open the head, but it took a lot of force to get the tailcap off the light when inserting the battery, so I would assume that the head is just tightened very hard. I don't see any glue from the inside either.
Then it's probably glass with plastic AR coating.
Thanks, mfm. That had to take a while to put all of that together, let alone the time it took for you to run around to all of those different countries. I didn't even realize the extent to which UV is being used in notes, but it was fun seeing all the different possibilities.
Comparison added to the first post.
I wonder if the T5 light is a bit underpowered, I run it with 4 x Eneloop AA but the voltage for the T5 tube should be 6V (the manual says to not use rechargables but that's usually crap). May have to find some alkalines just to try, don't have four of them at home.
Looks like the TK is better regardless of the voltage to the T5.
It's not only that the T5 is weaker, it also seems to not cause fluorescence at all in some of the places the TK does.
But maybe it really is just the input power.
I tried with four alkalines today and no noticable improvement, as expected.
But it seems to me that that the T5 causes fluorescence in all the same places as the TK? Just weaker and it's not that easy to see on the pictures (and the green part of the euro is very hard to see because of the violet light).
Even though this 4W version is a little hard to use because of the visible light, generally there is no doubt that fluorescent tubes are way superior to LEDs for generating 365nm (or lower) UV. Even if you buy a Nichia drop-in for 160 EUR it will be easily outdone by a fluorescent lamp costing much less (but the LED is easier to bring with you).
I really need to buy a fluorescent one some day.
Where did you buy yours? I remember a seller on eBay that had them but I can't find him.
There's also a comparatively cheap 254nm version: http://cgi.ebay.com/254nm-Ultraviolet-Pocket-Lamp-Shortwave-Bonus-M12_W0QQitemZ370510530344QQihZ024QQcategoryZ3226QQssPageNameZWDVWQQrdZ1QQcmdZViewItem#ht_3228wt_1139
I wonder how safe it is... and how effective it is.
I bought this one, it's even cheaper now than when I bought it: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280590817370&ssPageName=STRK:MEWNX:IT
But you don't need it if you have the TK...
Shortwave UV is much more dangerous so I wouldn't bother with it. With high-powered shortwave UV you must have both eye and hand protection, maybe the 4W isn't that powerful but anyway. I already had enough trouble from the lights I own, briefly I looked into the 3W drop-in without thinking when I had the protection glasses on (not a great idea).
Here is how bright a banknote fluorescences under a high-powered tube light, I would guess it's a 16W or 20W tube: http://www.youtube.com/watch?v=JNKkCmXBAg8&feature=related
Looks like the TK is the only one worth bothering with. The UK mint warns that no LEDs are likely to give short enough wavelength light to check the security features
It seems that some of the pictures with the TK-566 were taken when the battery was low (AA powered has it's drawbacks), I have uploaded new pictures of the 500 CZK and 1000 JPY notes.
Thanks mfm! Wow, this is an incredible amount of effort. You really outdid yourself on this one. Nice collection, and incredible shots!
Frontpage'd and Sticky'd for sure.
Thanks!
I added some more shots: the 5 USD vs the 20 USD and some more Czech and Swedish banknotes.
Thanks for all of your hard work mfm! 
They really are great photos, it's a little glimpse of something we normally don't get to see. Which is rather a shame as they really are very nice.
Random question...I know some insects can see UV, bees for instance. What would they see if they looked at these notes in day light?
It's not something I've thought about before so it's intrigued me, would they see nothing as we do or would they see non-glowing marks.
I assume the ink that the marks are made with is transparent to visible light, but perhaps not to UV..but really I've no clue :P
I added the backsides of all current Chinese banknotes, I think they are quite nice.
I really like the performance of the TK-566 and am interested in buying one for my mom who is a bit of a geek when it comes to such things. She's familiar with the dangers of such things and would know better than to look directly into the light. Outdoors in the dark, what is the range of this light? Is it best for up-close only such as checking bank notes? Tomato worms are known to fluoresce under a blacklight and she wants something that could be used to sweep tomato plants after dark looking for them. Which UV lamp would be the best projector?