How can the layperson test whether a UVC light sold as "germicidal" is a fake or probably the correct wavelength?
You can do the banana test to identify if it is real or fake.
Get a green banana and cover parts of it with a sticker you now need to expose the banana with the uv light for about one hour,the green banana will get brown/yellow at the exposed part and stay green under the sticker if the uv-c light is genuine..
It is best to do this in a dark room and the banana can not be in a plastic bag or any covering as this might stop the uv-c light.
The uv source needs to be close to the banana for this to work.
If the color of the green banana stay the same after the test your uv-c light is fake.
Never look directly at the uv-c light and do not shine the light on your bare skin.
source https://www.reddit.com/r/BigCliveDotCom/comments/gj9ymb/uvc_the_green_banana_test/