You will love this, my girls wear it for night time walks and it is bright.  I love the purple one as it's closest to hot pink.  If you order, this company is usually about 2 weeks out on arrivals, but it's worth the wait.  It is an Australian designed brand!  If you have a chihuahua, pick small through medium.  If you have a Pitbull, pick small through large.  The item comes like that because you will actually cut the product down to fit.  Cut little by little off first.  Make sure it's not too tight.  It's not to be worn all day long, so it can slip over the head if necessary, I don't let it slip over the head, but I do allow 3-4 finger space between the skin.  A nice relaxed fit.

Night Walking Lighted Tube for neck