Working with glow-in-the-dark yarn

Dear users, dear designers,
have you already worked with glow-in-the-dark yarn? Do you have any experiences you’d like to share here?

Oh yes, I really love working with it. In keeping with the theme, I’ve already crocheted a firefly, as well as a big, cuddly pillow shaped like a car and some unicorns, and I’m also incorporating some into my patchwork quilt, for which I’m currently knitting squares.
However, the effect is only truly spectacular when you shine a flashlight on it—it glows only very faintly in normal daylight.
I can’t say yet how it will look after a wash. Why does the yarn glow? Is it treated with something that might wash out? And what about stuffed animals for kids who still put them in their mouths? I have no idea about that.

“Glow-in-the-dark yarn” is a misleading term, because the yarn itself doesn’t glow. It contains a substance that strongly reflects light.
There are also chemicals that reflect light while slightly altering its wavelength. These are called optical brighteners. Manufacturers often add them to laundry detergents to make clothes appear especially white, because the fabric reflects ultraviolet light as visible light.
Something similar happens under black light, for example in nightclubs. There, too, certain substances are made to reflect in the visible spectrum by light that is invisible to us.

I would primarily use reflective yarn for winter hats and scarves. The yarn reflects light, such as headlights, and drivers will hopefully then recognize that there is a person out and about in the dark.
These days, the dyes used are no longer harmful to health.

Hi, last fall I knitted hats out of it for two of my grandchildren. That way, they’re easily visible on winter mornings on their way to preschool and school. 

There is also “self-luminous” yarn. However, it needs to be “charged.” You shine a flashlight on it (in the summer, sunlight is sometimes enough), and then it glows in the dark. How long the effect lasts depends on the intensity of the light it was exposed to.
According to the manufacturer, it’s also safe for children.
Here’s an example of self-luminous yarn: