It’s increasingly difficult to come up with an application in the modern day that doesn’t make at least some use of simple LED indicators in one way or another - or many ways at once. However, we’ve seen questions recently wondering why some of these devices that appear to have simple white or colorless lenses, such as LTL-293SJW, show fluorescence under a UV light source. Is this intended? Why?
In short: This is not intended but is also not considered an issue. Manufacturers test and specify these devices under normal lighting conditions, not UV. Any fluorescence on the products is untested for and may be from residues from manufacture or assembly, or even shipping. Because the fluorescence is not intended or controlled for and has no effects on the product’s performance, it’s considered a bit of a nothingburger - a neat if vaguely baffling happenstance, but otherwise irrelevant. Applications expected to be subjected to constant strong UV exposure should likely be looking into alternative products as befits their intended use case.