2mm ZWB2 filter tested (visible light blocking filter suitable for 365nm UV flashlights)

disclaimer: I could have sufficed by just remarking: yeah, it works fine, but I can not resist doing a proper test, even for a simple optical filter

In the the double-UV light group buy, this 20mm diameter, 2mm thick ZWB2 filter was discussed as a way to get rid of the large amount of visible light that chinese 365nm leds (and the Ledengin LZ1 365nm is just as bad) produce as an unwanted by-product. Being 20mm diameter it fits in the Convoy tube-style lights as replacement lens. It is for sale on Ali-Express for $16.66 dollar and I bought one to test (with the kind help from BLF-member khas because I can not buy there myself). The above picture shows the filter placed on top of a normal white led flashlight: apart from transmitting UV with a peak at 365nm it transmits in deep red as well (the reproduced colour is not accurate btw), here's the transmittance graph (from the selller's page) of a 1mm ZWB2:

You loose a bit of light (this graph is for a 1mm filter, my thicker 2mm filter reduces the transmittance at 365nm a bit more: to 75%) but apart from that it should be pretty ideal, let's test that!

First the set-up, because how tests are done are always important for interpretation of the results.

The test subject is a 50 euro bank note because it shows several colours of fluorescence at 365nm, less at 400nm. The lights used for testing the filter have the following leds: 1)400nm generic chinese 3535 led, 2)Nichia 276A U365, 3)Ledengin LZ1 365, 4)Royalighting RY-3535P 365nm (the chinese 3535led sold by intl-outdoor).

The yellow glasses are for protection of my eyes during testing, the clear glasses (Bollé impact-protection glasses) is a pretty good UV-blocker, needed in front of my phone camera because it picks up light further down UV than my eyes do, with them what the camera sees is pretty much what my eyes see (with the 365nm leds that is, getting the 400nm correctly imaged was not really possible) :

The left picture was taken without the glasses before the camera, that purple glow is invisible by eye, the right picture was taken with the glasses before the camera, this is quite what I actually see as well (illumination was the RY-3535P with ZWB2 filter).

The test:

Mind that in the following pictures the output differences of the various leds, even though that did not differ to great extend, and the slight reduction of output caused by the filter is not captured (I used an auto-exposure on the camera with reduced brightness).

The note with white light:

400nm UV, I used the ZWB2 filter to get a bit more contrast, but for my eyes the blue and green fluorescence of the fibers (the red fluorescent fibers can only be seen at 365nm) is stronger compared to the purple background and of more distinct colour, I can not get this right on image: it is better in real:

Now on to the 365nm lights, the rest of the pictures are reproduced pretty well from what my eyes see, apart that the camera does not pick up the difference between the blue and green fibers as well as my eyses:

Nichia 276A U365 without filter. You can see how good this led is, hardly any visible light to spoil the fluorescence:

Nichia 276A U365nm with ZWB2 filter. The filter still does some good, the minimum amount of visible light is filtered out, and some of the 'upper flank' of the spectrum is reduced as well, removing some purple glow still picked up by the camera in the above picture without filter (but this purple was not seen by eye):

Ledengin LZ1 365nm without filter. This led is known for its very good output at 365nm, but also for its massive amount of white-ish light as well, as can be seen:

Ledengin LZ1 365nm with ZWB2 filter. That fixes a lot!! This filter gets the illuminiation quality on Nichia level :-) :

RY-3535P 365nm without filter. This led has the same problem as the Ledengin LZ1 365nm, good fluorescence but with lots of white-ish light, a bit more even:

RY-3535P with ZWB2 filter. Also here the filter helps out to get the illumination to Nichia level! In my test of this led a year ago I found that the peak wavelength of this led is 370nm compared to 365nm for the LZ1, but you do not see that difference in the fluorescence of a 50 euro note:


This filter does a very good job blocking visible light that comes out of the various 365nm leds that emit in white as well, and even for the Nichia 276A U365, that hardly produces white light it also helps a bit. It is not suitable for 400nm light, it blocks a lot of the usable light and 400nm leds do not have the typical 'white light pollution' anyway. For an optical filter it is really cheap (long ago I used to work in an optics lab, from the major manufacturers any optical filter starts well above 100 euro), but as a flashlight upgrade $16.66 is considerable. Still, for the enthousiast I think it is a good buy. :-)

Did I mention it looks cool in your flashlight? :

Odd, when I signed in to Ali it took me to this page:

and also this: http://www.aliexpress.com/item/2pcs-10mm-ZWB2-Glass-Ultra-Violet-UV-Filter-Pass-Ultra-Violet-Block-visible-light/32410736012.html
two 10mm filters

That must be a medieval type of not so smart advertising: when several people suddenly start viewing a page (like when a thread is started on BLF about a product ;-) ) everyone else is offered that page immediately.

Thanks djozz. Do you know if the shop takes PayPal?

Being an Ali-Express store, they do not accept Paypal. I understood that Simon from Convoy flashlights on Ali-Express does Paypal if you mail him, but I doubt that these guys do that, the filter came with an all chinese business card from Beijing

Thanks for posting that. I did some searching a few weeks back for a small UVA bandpass filter but didn’t have much luck. They were either too large or too expensive for my experiment, or the pricing wasn’t transparent and I didn’t want to give out my email address just to get a quote.

I’m testing an ML8511 UV sensor to help indicate when a 6000 watt mercury vapor lamp is at the end of its life. I was looking for a filter that will reduce some of the UV radiation getting to the sensor and this little filter might be perfect.

I was planning to shoot a video in the forest at night and i want to use IR LED light but which spectrum is good at it? 850nm or 940nm?

Nice review djozz. It just seems like it was last week when we were talking about this filter. It’s nice to know that it can filter out that visible light from the RP-3535 and the LED ENGIN.

After looking around I found another store with a good deal. Is 3mm too thick? Too bad it’s not 1.5 or 2mm.

2pcs 20mm ZWB2 Glass Ultra Violet UV Filter Ultra Viole high transmittance

Price: US $19.90 / lot
2 pieces / lot , US $9.95 / piece

Shipping: US $2.51 to United States via ePacket

Total Price: US $22.41

2pcs 20mm ZWB2 Glass Ultra Violet UV Filter Ultra Viole high transmittance


Diameter: 20mm

Thickness: 3mm

Material: glass

Quantity: 2 pieces

Spectrogram is as follows (Please see the green line ZWB2):

Ah, I’d managed to forget about this being 20mm — the right size for Convoys, thanks for the reminder.

I’d guess the 3mm filters would be significantly worse (perhaps why they’re on sale).

Anyone seen 1mm filters anywhere?

I have ordered two 10mm x1mm filters, but they are still in the mail. I will give an impression when they arrive!

Somebody is going to build a UV pen light before I do. I was thinking of using a Hugsby as my host. They come apart easy.

My host will be this AAA light , but you still may be faster than me because I do not have an emitter for it yet:

but, see also next post..

A few days ago two 15mmx2mm diameterxthickness ZWB2 filters arrived. When I ordered them I did not know of a host yet with 15mm lens, and there appear very few of them! Today I rembered I had an old Romisen AAA RC-F7 (build quality=crap) with a blown switch that might be the right size. Took me half an hour to find it in my rubbish and indeed the lens diameter was 15mm. Managed to repair the switch and mod the light with a led4power 365nm led and ZWB2 filter. Used an ordinary 14mm aluminium MCPCB that I had around and the stock 1 mode little boost driver. It draws 700mA from a partly drained Duracell alkaline AAA, so there's maybe 150mA current leftover through the led. But it works fine, perhaps 1/5th the output of the BLF-A6 that I modded with the same led at 700mA led-current and 20mm ZWB2 filter, best light I have ever seen for banknotes and it is even a bit throwy because of the small die :-)

I just gave this info to Karen from Gearbest to see if they could start carrying this. With the new Convoy S2+ being released soon, this would be a popular and inexpensive item. Maybe twice the cost of a 20mm AR lens ? Banggood also has been given the info a while back.

ZWB2 光学玻璃 滤光片 紫外线透过玻璃 紫外滤光片 20*2mm ¥ 25.00 ( 约USD 3.93?)

More sizes here.

That would be great, and if they go for it, I wonder what they charge. :-)

The first link has a price and says that it is a ZWB2. The other link only says IR, so I’m not sure about that one.

Don’t forget to send me a coupon for the group buy.

I’d buy one!

An affordable filter and the new Convoy S2+ with Nichia UV would be a great combination. Banggood should include one for free with every one of those old stock Convoy S2 with Chinese UV emitter. If they don’t, they will never get rid of them after Simon releases his new UV lights.
Convoy S2 365nm UV Single/3/7 Modes SMO Reflector LED Flashlight

any cheap/english websites selling those filters ? i am looking for 18mm lense.