It took 12 days arriving here. This product is a perfect bandpass filter. That is, it lets through the 365nM UV B and blocks almost all visible light (it is a very good match for the UV LED). This is great for observing fluorescence - minerals, dyes, scorpions, glue, etc. Without a filter these diodes produce a lot of visible light that washes out too much fluorescence.
The filter makes the my flashlight(from Dankung too) UV light much more useful.

Very fast delivery. The ZWB2 has greater transmittance at the LED's peak emission frequency and will actually allow more UV light through. Thank DANKUNG for multiple diameter options. I searched the whole internet only found 4cm filter here.